Hooded Crane Origins

Where did the Tennessee Hooded Crane come from?

Apparently this is much on the minds of the North American birding community. Through yesterday there had been 922 visitor-days tallied on the sign-in sheet at the observation platform at Hiwassee NWR since the crane first arrived in mid-December; these visitors have come from 38 states and several foreign countries. My wife and I stopped by on our way to Atlanta a few days ago and were rewarded with leisurely views of our state's current celebrity V.I.B. Opinions vary quite a bit as to what the source of this bird might be; one youtube video appears to suggest that he or she came from Planet Claire.

My initial knee-jerk reaction on hearing of the bird was "that's gotta be an escapee." But as I have learned more, I have shifted from this starting point. There are two critical questions:

1. Is it there a reasonable scenario under which a wild Hooded Crane would arrive in Tennessee without human assistance?

2. Is there a plausible source for an escapee?

My feeling is that if the answer to (1) is yes and (2) is no, then my vote for the bird (I am on the Tennessee Bird Records Committee) is "accept;" otherwise it is "reject." I am still very much in exploratory, open-minded mode about this. But here are some of the most interesting things I have come across:

Much was made of the escape of three Hooded Cranes in Idaho a few years back (date appears to be uncertain). However, it seems fairly certain now that these birds were pinioned and thus could not be the source of either the Tennessee or Nebraska birds in 2011.

The total zoo population of Hooded Cranes worldwide is very small (I have seen the number given as 84), and no escapes are known. The number and status of birds in private collections I have not seen so much about, but there are not going to be many. As I saw it described, "The Hooded Crane is a rare and valuable species and usually in a very secure setting." This means banded and probably pinioned.

There have been long-distance vagrant Hooded Cranes seen in Asia. There are records from Kazakhstan and eastern India, both at least 1000 miles from the usual breeding and wintering areas. If you go only slightly farther to the northeast rather than west, you are in mainland Alaska, and certainly in potential contact with U.S.-wintering Sandhill Cranes.

John Vanderpoel, in a recent blog post, describes the movements of a family group consisting of a Sandhill Crane, a Common Crane, and hybrid offspring. He says that they were Siberian nesters that were seen in the Jasper/Pulaski refuge in Indiana, the Yukon Delta (headed west), and Nebraska. If he has the facts correct, this would seem to make the "wild Hooded Crane comes to Tennessee" scenario very plausible. Many people have doubted whether a wild Hooded Crane could make contact with the Sandhills that winter in Tennessee. Considering that many of the Hiwassee cranes also pass through Jasper/Pulaski, it's only a couple of small steps from the travels of this wild CommonHill Crane family to plop a wild Hooded Crane at Hiwassee (and Nebraska last spring). Remember that this is not a Sandhill Crane and it will not necessarily be tied to the traditional migratory patterns of the Sandhills. It is also an unmated bird, which has a long summer to wander solo in the north.

In recent years there have been Common, Hooded, and Demoiselle Cranes found in the U.S. in the company of flocks of migratory Sandhill Cranes. If these are all escapes, why are they all species that nest in central and eastern Asia, with none of the African or Australian species (some of which are also common in captivity)?

As I said, I remain in investigative mode and am a good ways from casting a BRC vote, both intellectually and temporally. The evidence at this point is definitely trending towards "wild" in my mind; but that could change. Additional information, especially about captives, would be extremely welcome.

ADDENDUM

I've been looking in to the Common Crane scenario more, and here is what I have found in back issues of North American Birds (it is more complicated than what Vanderpoel wrote). If anyone has corrections or expansions to this info, by all means let me know:

Fall 1998: Alaska's first Common Crane in 40 years is found in Delta Junction in a (Lesser) Sandhill staging area. This is southeastern Interior AK, far from the Yukon Delta or Siberia.

Spring 1999: Common Crane at Kearney Nebraska invites speculation because it "shared the pale plumage worn by [the] bird found last fall in Delta Junction." Bird in the company of Sandhills, mostly arctic-nesting Lessers.

Fall 1999: Common Crane mania in Quebec. One adult associating with a Sandhill and two juveniles of possibly hybrid characters. Meanwhile elsewhere in the province, two 1-year old Common/Sandhill hybrids found. This is Greater Sandhill territory, though the subspecies of the Sandhill mate was not determined. Speculation that the adult might be the same bird seen several years previous on the Atlantic coast of the U.S. and determined to be an escapee of known origin, along with two years' worth of its hybrid offspring. No connection presumed between this bird and any wild birds from western North America. Later, though, this escapee was found to be happily resident and reproducing in New Jersey and not wandering in Quebec (see below, Winter 2000-2001)

Fall 1999: About a month later, a Common Crane appears at Jasper-Pulaski in Indiana, the major staging ground for Greater Sandhills. The bird is in the company of an adult Sandhill and two juvenile hybrids. Initially believed to be the same as the Quebec bird, but then the adult Sandhill was determined to be a LESSER Sandhill. Suspicion then turns towards its possibly being the same bird seen in Nebraska in the spring. Birders farther south eagerly await the arrival of the Common Crane with the migrating Sandhills; however it is not seen.

Spring 2000: A Common Crane appears in Nebraska in the company of a Lesser Sandhill Crane and two apparent hybrid youngsters. Could the Indiana family have found its way back to Nebraska???

Winter 2000-2001: An SA report in the Hudson-Delaware region details that there is a small resident population of Sandhills, the original escapee Common Crane, and numerous hybrid offspring in New Jersey. So this escaped bird does not account for the Quebec or Indiana birds.

Of course it is not definite that ANY of these birds were the same individual, or than ANY of the eastern birds were wild (western birds are generally presumed wild). One thing it does make clear, though, is that some Lesser Sandhills do reach Jasper-Pulaski. The similarity to the sequence of the three recent Hooded Crane occurrences (ID spring 2010, NE spring 2011, TN fall 2011) is interesting. It does appear to suggest that a wild Common Crane made it over from Siberia, paired up with a Lesser Sandhill, and travelled to Indiana (and presumably farther south, as it disappeared from Indiana in November).

Hooded Crane in Tennessee

I'm sure this news is buzzing through the birdosphere already!

An adult Hooded Crane was found today among the wintering Sandhill Cranes at Hiwassee National Wildlife Refuge in east Tennessee. For those unfamiliar with the species, this is a bird of southeastern Siberia and elsewhere in the far east. It is endangered in the wild, and also kept in captivity in North America. Amazingly, this is the THIRD Hooded Crane sighting in the U.S. in recent years, after one in Idaho in 2010 and one in Nebraska in April of this year. Discussion will doubtless continue for a long time about the possibilities for wild versus escaped origin, the odds that the Tennessee bird could be the same as the Nebraska and/or Idaho birds, etc. But whatever its origins, this is a rare and beautiful sight, bringing the total of crane species currently residing at Hiwassee to three (though only one is presently ABA-countable).

Woodpecker Wingbeats Revisited

I didn't really want to dredge all this old stuff out again, but it has remained a point of contention and misaprehension, and of course there are some new datums to consider.

Years ago I posted a graph of some comparative wingbeat data between the bird in the Luneau video and some known Pileateds, without comment. Well, it seems time to repost this with additional data, and with comment. I have added the two launch sequences of the Imperial Woodpecker, and the data presented by Louis Bevier for his best (fastest, most Luneau-like) Pileated (click image for a larger view):



First some comments on the Bevier data (for those curious my original response to his articles is here). These have only been presented in very limited, summary form without the actual videos being made available. I realize that he is operating on the notion that he only needs to find one Black Swan (to refute the statement that All Swans Are White), and feels that there was no need to lay out extensive results. But the swan in question was described in a somewhat roundabout way, and on closer inspection it kinda begins to look sort of whitish, really. The main point of fogginess is the way he expressed the wingbeat frequency data, which initially suggested that the flap rate of this champion flapper Pileated only dropped from 8.8 Hz to 7.5 Hz over 12 wingbeat cycles. But the numbers he gave were cumulative through 12 cycles, not the individual value for the 12th cycle. Reworked from the data points given, you get what I have plotted, showing averaged of 8.8 Hz for cycles 1-5, 7.4 Hz for cycles 6-9, and 6 Hz for cycles 10-12, which is a much more substantial dropoff than suggested by the data as originally presented. One also has to wonder at the comparison between captive birds being released from human hands versus a free-flying bird launching from a tree; both the starting dynamics and the bird's likely mental state would seem to be very different between the two. Jumping (dropping? being tossed?) from human hands is a pretty strange way for a woodpecker to initiate flight; on the other hand, flushing from a tree trunk in response to the approach of a couple of guys in a jon boat propelled by an electric trolling motor is a rather ordinary experience for a woodpecker in the Big Woods, I'd expect, and not likely to trigger extreme behaviors.

Next, some general comments about the graph. Like the earlier graph, it shows the Luneau bird holding steady and flapping the fastest of them all, with very little upward curve to its line (upward= slower wingbeats). The Pileateds start out near it, but tail off after several wingbeats. Even the Bevier bird does not in fact keep up (in contrast to the assertions at the original site), falling increasingly behind just like all the others. The Imperial lines bracket the Pileated data for the most part, but the salient feature here is that it also does not tail off (slow down), remaining steady and straight.

I have maintained all along that wingbeat rate per se is not an especially strong or informative piece of evidence, as it is just one tidbit of data about flight dynamics and many things can affect it. What I find more informative are the mechanics underlying these changes (or lack of changes) in wingbeat rate. There is a qualitative feature of Pileated flight that causes this tailing off in wingbeat rate. After around 3-7 wingbeats, all the launching Pileateds I have seen videos of begin inserting brief closed-wing pauses in the upstroke between flaps. Initially these pauses are too brief to be obvious to the naked eye, but they are clearly evident on slow-motion video. As the flight proceeds the pauses grow into visible bounds (closed wing ballistic flight segments) separated by discrete flaps, which we all know as the classic Pileated cruising flight. It is the insertion of these discrete pauses that causes the apparent slowing of the wingbeat rate, not a dramatic reduction in the rate at which the wings are being moved during the flap. Again, all Pileated videos I have seen show this. I would expect the Bevier bird shows this too given its rapidly dropping flap frequency.

The Luneau bird does not display this flight behavior, which is why its flap rate holds steady. The Imperial does not display it either, with steady flaps until it either leaves the frame or closes up into one, discrete, readily visible bound. At the end of the one bounding segment that is shown until its end, the Imperial then resumes unbroken rapid flapping without pauses. It is worthy of note that in the Luneau video, as the bird reappears between trees in the later segments, it is always showing steady wingbeats, even at the very end. No closed wing bounds or pauses are discernible, though admittedly it gets hard to judge. This presence or absence of these brief upstroke pauses is a discrete qualitative difference between the flight styles of these birds, not a mere quantitative variation. It is a much "harder" distinction than the smallish differences in flap rates. I suspect that if this discussion were about virtually any other species of bird (even continental hyper-rarities), this type of feature would be readily promoted and accepted as a diagnostic character for resolving identification questions.

Summary: The flight of the Luneau bird is inconsistent with what appears to be the characteristic, even diagnostic, flight style shown by every Pileated video I have found. It is somewhat faster, but otherwise consistent, with the flight of the Imperial Woodpecker (in the one film that exists). Louis Bevier's "black swan" fast-flapping Pileated appears to be in front of a metaphorical and rhetorical bright light that makes it appear black; its actual color cannot be judged from the information available.

The Imperial Film

Note: Those who did not come here via Cyberthrush's blog might be interested in the debate between me and David Sibley on these matters in the comment section of this post.

Also note: My subsequent post elaborates more on the wingbeat rate and flight dynamics issues.

As should be widely known by now, the legendary film of a female Imperial Woodpecker shot in Mexico in the 1950s has finally been published and is available for all to see. Contrary to the conspiracy theories advances by Scott Crocker and others, this film does not in fact undermine the claim that the infamous video shot by David Luneau in Arkansas in 2004 is an Ivory-billed Woodpecker. In fact, even on first viewing, it would appear to support the Luneau et al Ivorybill claim.

The Lammertink et al paper covers the film itself, its history, and the present-day circumstances at the spot where it was filmed; I will not delve in to that here. Please read the article and view the video at the site I linked above if you have not already done so. My focus here will be on the impact this film has on analysis of the Luneau video, as it fills a major data gap that seriously impeded that analysis until now: the lack of any films of Ivory-billed Woodpeckers in flight for comparison. Of course, the Imperial Woodpecker is not the same species as our North American Ivorybill, but it is very closely related. I don't have the reference at hand, but wasn't there a recent genetic study that found that the genetic distance between the Imperial and the North American Ivorybill was about the same size as the distance between the Cuban and North Amercian Ivorybill subspecies? I believe it is fair and justifiable to use the Imperial as a close analog to what our Ivorybill would have looked like on film.

For the record, I had no advance access to this film. I saw it for the first time on the day of publication last month, same as everyone else. So I have not had months or years to examine it, nor were any of my earlier conclusions about the Luneau video influenced by having viewed the Imperial film, having spoken to anyone who had viewed it, or even having heard any credible rumors as to what it contained.

All of my previous analyses of the Luneau video can be reached from this link which is the same as the one in the right-hand sidebar on this blog. I will take this work as read and will not repeat it in detail, simply refering to my important conclusions and findings. Anyone who read my work could tell that I had very strong leanings towards an Ivorybill identification for this bird, and found multiple major and fatal flaws in the Sibley et al analyses that concluded that this video was consistent with a poorly-imaged Pileated Woodpecker. However, the lack of any suitable Ivorybill comparison material left unresolved dangling issues in several areas that have stopped me from proclaiming that this bird was definitively an Ivorybill. These issues fell into two areas: the launch sequence, and the flight mechanics (structure and pattern of wingbeats).

Launch behavior

First, to the launch sequence. This focuses on Infamous Frame 33 of the Luneau video, when a flash of white appears from behind a tree trunk just as the bird launches in to flight. The Cornell interpretation has been that this is the white shield on the back of the bird, and they used this to estimate the size of the bird. Sibley et al felt this flash showed the underside of a raised wing, and my own examinations of launch sequences of Pileated Woodpeckers led me to agree with this alternative interpretation. However, in contrast to Sibley et al, I found that the subsequent frame strongly suggested that the trailing edge of this underwing was white, not black, and that all the supposed black trailing edges they identified in the entire video were nothing but edge artifacts created by the digital imaging process. Hence even this alternative interpretation pointed to Ivorybill, not Pileated.

Now having seen the Imperial film, I have to say I may have been mistaken in disagreeing with Cornell's interpretation of this sequence. The behavior shown by the Imperial in the two launch sequences in the film is a very good match for the Cornell hypothesis and very different from that shown by typical Pileateds. Of course, as I mentioned before, both interpretations (when you stop misinterpreting imaging artifacts as plumage) come down on the Ivorybill side of the scale; but the Cornell interpretation is much stronger in both providing an unambiguous view of the "white shield" and in giving a size estimate that is outside of the Pileated range and right on for an Ivorybill. So this is a much heavier brick in the Ivorybill tray.

Flight mechanics: Flap rate

Discussions of the flap rate of the bird in the Luneau video generated a great deal of controversy. Its wingbeat frequency was higher than that shown in any of the Pileated Woodpecker comparison material available; in spite of claims of unpublished videos showing otherwise, there has still not been a video of a Pileated Woodpecker presented to the public in which the bird achieves and sustains such a rapid wingbeat rate. Of course, the real problem was that there was no film of an Ivorybill in flight to indicate whether or not this species actually possessed a rapid and sustained flap rate. Sibley and others argued that as a larger species, it should be expected to show a slower flap rate.

The Imperial isn't an Ivorybill, but it is very closely related and even larger. As discussed by Lammertink et al, it shows a very fast flap rate, considerably faster than what is typical for a Pileated. In the first 5 wingbeats of the second flight sequence, it achieves 8 flaps/second, nearly matching the Luneau bird.

I think we can safely conclude now that the Ivorybill had a fast, sustained flap rate, significantly faster than that of the Pileated, and likely extremely close to what the Luneau bird shows.

Flight mechanics: Wingbeat patterns

The flight of a Pileated Woodpecker after launch typically consists of a short series (3 to 7) of fairly rapid wingbeats, then a break into bounding flight where individual or paired wingbeats are separated by bounds (periods when the wings are folded in to the body and the bird functions as a ballistic missile). Sustained cruising flight of a Pileated generally continues this pattern of discrete flaps separated by bounds: flap....flap,flap....flap....flap....flap...

The flight of the Imperial contrasts sharply with this. In the first flight sequence the bird executes 7 wingbeats without a break before it moves out of sight. In the second it completes 15 steady wingbeats then executes a bound. After the bound, it resumes steady flight with 5 more uninterrupted flaps before it disappears from view. In the final sequence, the launch is not visible. When the bird appears in frame it is in steady flight, and completes at least 12 wingbeats before closing up into a bound and "cannon-balling" until the end of the film. One could describe the flight of this bird more as "flapapapapapapapapapapapapap.....flapflapflapflapflap"

The Luneau bird is in view for 4 seconds from launch to its final diappearance. It passes behind trees intermittently during this time. It is in continuous view shortly after launch for about 1.2 seconds, during which it completes 10 uninterrupted flaps without a hint of bounding flight. For the rest of the video, every time it reappears between the trees it appears to be engaged in steady wingbeats without bounds. There is no point at which the wingbeats appear to have stopped or even be separated by brief bounds. The bird completes 23 visible wingbeats during these 4 seconds; if you watch in slow motion and count along with the rhythm there seem to be no breaks, and interpolating behind the trees yields about 27 flaps in this time. This is a far better match for the Imperial than for a Pileated.

Flight mechanics: Wing movements

The film is shot at 24 frames per second (fps) which means that there are only a few frames (typically 3-4) representing each wingbeat. Hence, in any given wingbeat there are only a few wing postures shown. However, each flight sequence shows multiple wingbeats, and the adjacent flaps are often viewed from a similar angle and occur at about the same rate. However, as the flaps and camera shutter are never in perfect synch, each successive wingbeat is imaged at different point in the flap cycle. So, one can composite several adjacent wingbeats to create an approximate representation of what a single wingbeat would have looked like had it been shot at a higher frame rate. This is similar to the manner in which films of rotating objects (vehicle tires, fans, etc.) often will appear to show the object spinning in slow motion, or in reverse. I have constructed these composite wingbeats for two of the three flight sequences in the Imperial film, with interesting results. The second sequence yields the most attractive result, whith three successive flaps combined in to one:



Note that the bird jumps around in the frame, and the background does all sorts of distracting things. But if you concentrate on the bird, this yields what looks like a pretty fair representation of a singe flap filmed at 72 fps (by a very shaky hand).

The third flight sequence yields an interesting composite (again three separate flaps combined for a simulated frame rate of 72 fps):



In this case we see the bird almost directly from behind.

The first flap sequence does not yield a good composite. The bird traveled far across the frame, and the flaps were almost in synch with the shutter so there is less of an effect of each frame filling in the gaps from the others to create a smooth wing motion. And for purposes of comparison with the Luneau video, this side-on viewing angle is perhaps the least informative of the three.

Note that both of these composite sequences show the bird in cruising flight, not during the initial takeoff and acceleration. The salient feature notable here is the relatively shallow nature of the wingbeats compared to Pileated flight. The wings are not fully opened on the downstroke until they are at about a 45 degree angle, and they are draw in rapidly at the bottom of the stroke without being fully extended downwards. This is of course exactly what is shown by the Luneau bird and is not typical of Pileated flight.

Flight mechanics: Bowed wings

One of the salient features I found in the Luneau video that was inconsistent with Pileated flight was the manner in which the bird bows its wings downward during the downstroke. This is not apparent in the two composite sequences of the Imperial flight shown above. However, it does appear earlier in the Imperial flight sequences, most prominently in sequence 2 while the bird is accelerating and banking. A final composite shows the bird in mid-downstroke on 6 successive wingbeats:



The flap rate of the Imperial at this time was almost exactly 8/s, so the wings are imaged in nearly the exact same part of the cycle in each frame. Note that the bow increases as the bird banks, then flattens out when cruising flight is achieved. The wing bowing never looks as prominent as is shown by the Luneau bird, but it is present nonetheless. It also appears to be present in the side views of the first Imperial launch sequence in frames 654, 658, and 663. It does not show at all in the third flight sequence, which is missing the initial acceleration and also shows the slowest flap rate of the three.

The naked eye view

The frame-by-frame analyses are revealing about the behavor of the bird, but they do not necessarily reflect directly on what a birder in the field sees when a large black and white woodpecker flies off a tree and vanishes in to the forest. To give a suggestion of what this might all look like to the naked eye, I created a mash-up of 5 segments of fleeing large woodpeckers. I used the first two Imperial flight sequences, the Luneau Video, and two of David Nolin's Pileated videos. For the Pileateds I deliberately chose the two most Luneau-like of them, showing a bird executing rapid flaps and sustaining steady flight for the longest time before breaking in to bounding flight. The modern digital videos are deinterlaced at 30 fps (alternate deinterlaced frames); the Imperial film has been adjusted from 24 to 30 fps by duplicating every 4th frame (standard film-to-video conversion procedure). You likely will need to play this video repeatedly to take it in and start to get a sense of the comparisons between the birds. The mash-up is not intended to show detailed wing movements, etc; it is deliberately shrunken so you just get the quick flash impression, as though you were startled in the woods by stumbling upon one of these birds.



First to the marked similarities. All the birds explode from the tree in a barrage of rapidly flashing black-and-white. The differences in flap rate are not really discernible initially. And all take off like a chiropteran out of Hades. The Pileateds' breaks from steady flight to rapid bounding flight are noticeable at the end of their sequences on repeat viewing, but it is not a dramatic shift. Remember that I deliberately chose the two most Luneau-like (and also Campephilus-like) videos I had on hand for this comparison. The real contrasts to the naked eye would probably happen later in the sequence, when the slow bounding flaps of a Pileated would contrast sharply with the sustained rapid flaps of a big Campephilus (perhaps broken by well-defined bounds); but lacking a longer Imperial movie this is not knowable for certain. Overall I would say that in a place where a large Campephilus was known to occur alongside Pileated Woodpeckers, then a practiced eye could learn to distinguish the two species from a rapid naked-eye glimpse as they explode off trees and vanish into the forest based on flight gestault. Hopefully this situation will arise again somewhere in the future; at the present there is nowhere on earth that matches this description.

Conclusions

As I mentioned before, I have in the past generally hedged my declarations about the identity of the bird in the Luneau video, stopping just short of proclaiming what species the bird is rather than what I felt it was most likely to be. Enough of that.

The bird in the video shot by David Luneau in Arkansas in 2004 is an Ivory-billed Woodpecker, Campephilus principalis. I have no residual doubts, either personal or scientific. This species did not go extinct in 1945 or 1984, it persisted at least through 2004 and is quite likely still extant as I type these words. All the anomalies identified a priori (without foreknowledge of the Imperial film) in the flight of the Luneau bird that did not appear to line up with a Pileated Woodpecker do line up with the documented flight of an Imperial Woodpecker, the Ivorybill's closest relative. Combine this with the fact that there are no other discernable features of the bird that are inconsistent with the Ivorybill ID and several that do not match a Pileated (again, when you stop trying to make plumage markings out of image artifacts), and the case is closed.

I will echo what I said in some of my other Ivorybill posts. This creature is not a ghost, a fantasy, or a yeti. It is a bird. A very rare bird that is very difficult to locate and relocate. But it is a bird nonetheless, one that is probably alive and pecking on a tree somewhere within a few hundred kilometers of where I sit right now. Birders, ornithologists, and conservationists should treat it as such.

If any of these video links fail to function, please post a comment to let me know this so I can address the issue. I work over dialup so it is often hard for me to evaluate these things myself. Thanks!

Tennessee Breeding Bird Survey -- Summary

For me, major point to be gotten from 45 years of the Breeding Bird Survey in Tennessee is that the birds are doing pretty well, overall. Most species have shown increases in their numbers, and the non-native invaders remain a small component of the avifauna in most areas. The two most coherent trends are large increases in diurnal birds of prey and in a large suite of forest-dwelling birds that do not winter primarily in the neotropical regions. The former I would expect to be attributable to direct conservation efforts and increased cultural awareness; the latter strongly suggests a fundamental and substantial improvement in the amount and quality of forest habitat within the state. Even beyond these suites of species, trends average modestly upwards in most cases (even for the neotropical migrants).

Behind this happy picture there is a small suite of species that appear to be in serious trouble. Landscape-level habitat changes probably underlie many of these large declines; the same improvement in forest habitat will be linked to a reduction in edge and agricultural habitats. The exact mechanisms underlying these declines are doubtless unique to each species and are not always obvious. Some of these drops seem more drastic than simple habitat changes can account for.

One lesson I would also take from these data is: "Conservation works." Many of these optimistic trends really took off in the late 1970s; it hardly seems coincidental that this comes on the heels of the major advances in environmental legislation and programs that began in ernest in the early 1970s. Of course this can make avian conservation a victim of its own success -- why do we need all these programs when the birds are doing so well? This same ironic conundrum affects all successful programs. It still does not mean that we should overlook or downplay the successes and try to gloss over the fact that in total our state's breeding bird populations appear substantally healthier than they were 45 years ago.

The final lesson would be: "Past performance is no guarantee of future results." Many of these upward trends show hints of abating in the last decade, though it is too early to tell for certain. This may just be the wobbles of this varied and nicely-rebounded avifauna as it settles down into a new quasi-steady state in our improved, avian-friendly landscape. But it might not. Nothing can be safely taken for granted in this arena.

As a closing note, I should point out that I do not see any suggestion of a climate change effect in these trends. There is no pattern of species spreading preferentially northwards, southwards, eastwards, or westwards, as would be expected in response to large-scale shifts in climate patterns. This is not surprising, as the actual climate change signature in Tennessee's own climate records remains very small and difficult to detect statistically if it is there at all. One would expect these effects to show earliest and strongest in species that nest in areas experiencing the greatest changes, such as the far north. We of course only see those birds in Tennessee in migration and in winter.

Whatever the future may hold, we in Tennessee have headed in to the Third Millenium with a breeding avifauna that is on the whole diverse, robust, and thriving. Let's work to keep it that way.

Tennessee BBS index:
Introduction
1: Waterfowl to Herons
2: Vultures to Doves
3: Cuckoos to Woodpeckers
4: Flycatchers to Corvids
5: Larks to Wrens
6: Gnatcatchers to Waxwings
7: Wood Warblers
8: Towhees to Buntings
9: Icterids to House Sparrow
Ups and Downs
Habitats
Inflection Points
Summary

Tennessee BBS: Inflection Points

As I scrolled through all those graphs for the individual species, it became clear that 45 years was not only long only enough to show trends, it was long enough to show trends in trends -- the second derivative, not just the first. Few of the graphs show a simple up or down trend over the whole period, even when allowance is made for the year-to-year wiggles. American Goldfinch provides a stark example of this; Chipping Sparrow shows another. There appear to be three periods around which these inflection points cluster. I have had trouble making sense out of some of these; perhaps readers with more knowledge of the changes in land use, legislation, and other possible impacts in the mid-south during this era might shed some light.

Turning Number 1: Late 1970s-1980

Something clearly happened around this time. I discussed this earlier as the Great Sparrow Shift; it involves other species as well, from Goldfinches to Orioles to Herons. This is the time at which several of the woodpeckers and raptors began their impressive increases. Overall, for the species that seem to show a notable shift in the direction of their trend lines at this time, the large majority of these shifts are towards the positive. Many of these are weedy and edgy species, though a marked exception is the Gray Catbird, which began a sharp drop around 1980.

Turning Number 2: Around 1990

About a decade later, there was another shifting in the trend lines for a variety of species. This is a very mixed bag, with some increasing trends flattening while other flatlines started increasing and some species entirely changed directions. As with the first turning, the majority of the shifts were positive, but less dominantly so in this case. Wood Ducks, Chimney Swifts, Great Horned Owls, and Red-winged Blackbirds are among the species that began declines at about this time.

Turning Number 3: Early 2000s?

As it is close to the end of the current dataset, this third turning is less definite. Most of these suggested trends remain hard to distinguish from ordinary short-term wobbles. Still, there are indications of another shift in the trend lines for many species in the last decade. Unfortunately, most of these possible shifts appear to be in the wrong direction, or at least the flattening out of a long-term increase. There are some positives, including the surges in Tree Swallows and Mississippi Kites. The coming decade will tell whether most of these hinted-at changes are sustained.

I would expect these turnings to primarily be associated with landscape and habitat shifts. These could come about from official programs, economics, or many other factors. I would be curious to hear suggestions as to what these factors might have been.

Tennessee BBS index:
Introduction
1: Waterfowl to Herons
2: Vultures to Doves
3: Cuckoos to Woodpeckers
4: Flycatchers to Corvids
5: Larks to Wrens
6: Gnatcatchers to Waxwings
7: Wood Warblers
8: Towhees to Buntings
9: Icterids to House Sparrow
Ups and Downs
Habitats
Inflection Points
Next: Summary

Tennessee BBS: It’s the Habitat

As alluded to in the last post, the population trends of birds indicated by numbers from the Breeding Bird Survey in Tennessee appear to be related in some degree to the habitat requirements of each species. I looked at this in more detail by categorizing each species according to very general, landscape-level habitat preferences. The categories I chose were:

Forests -- relatively continuous and closed canopy forests. Occurs throughough the state, but most extensive in the eastern mountains and hill 'n' holler portions of the Highland Rim.

Edge/Mosaic -- the mosaic of woodlots, smaller farm and pasture areas, edges, roadsides, successional clearcuts, lower-density houses, and other mixed habitats typical of rural and less dense suburban areas that archetypally characterize much of Tennessee. Widespread statewide, and especially typical of the Highland Rim, hillier parts of the Coastal Plain and Central Basin, and the less rugged areas of eastern Tennessee.

Open country -- large-scale acriculture, with most land area in croplands and pasture. Characteristic of much of the Coastal Plain and Mississippi Alluvial Valley, the flatter inner Central Basin, and the Barrens areas of the Highland Rim. Small areas of this sort of landscape occur in most regions of the state wherever flatter ground occurs.

Residential/suburban/urban -- higher population density areas with lawns, “landscaping,” parks, commercial areas, etc. Includes centers of small towns as well as suburbs of large metro areas.

For each species, I checked off one or more of these categories based on general pereferences, not strict obligate requrements. For instance, Broad-winged Hawks are scored as “forest” and Horned Larks as “open,” but I have seen and heard both species from the exact same spots on our “edge/mosaic” farm in a Highland Rim hollow.

I also added a fifth category, both because it is of much interest in the conservation community and because a quick inspection seemed to confirm its significance. I checked off species that are neotropical migrants -- those migrants for which the majority of the population winters south of the U.S.

And as a final detail, when I calculated averages and other statistics on the percent changes, I used a logarithmic transformation in the form of X = ln(N_f/N_i) where N_i is the average count in the initial 10 years (1966-1975) and N_f is the average count in the final 10 years (2001-2010). This straightens out and balances the skewed nature of these ratios and gives them a more approximately normal (statistically speaking) distribution. Using the log metric, if one species has dropped to half while another has doubled, they will average out to zero. Using the straight percentages, they would average out to +25%. To give the final numbers, I converted these log transfomed averages back to regular percentages.


Averages by habitat type

When treated as described above, the following average and median changes come out for birds of each habitat preference:

Habitat	No. Species	Median	Mean
Forest	36	+74%	+101%
Edge/Mosaic	59	+35%,	+24%
Open	27	+15%	+32%
Residential	20	+67%	+71%

Though statistical tests do not make these trends significant, they confirm the impression that forest species are doing better than average. This gives a strong suggestion that one of the main driving factors for the rise in numbers of most Tennessee birds has been an improvement in the quantity and quality of forest habitat across the state.


The Neotropical Effect

When looked at in isolation, the difference between the neotropical migrants (NMs) and the non-neotropical migrants (non-NMs) was not significant. The 48 NM species showed an average increase of 21% (median 25%); the 53 non-NM species averaged 70% (median 75%). This appears to be a substantial difference, but because of the very large variability between species this difference is not outside the 95% confidence zone. Remember that individual species range from a drop of 99.8% to a rise of 69400% (excluding the three species that were not recorded in the 1966-1975 period and hence have an infinite percentage increase).

It is more revealing to look at the interaction between the neotropical effect and the general habitat preferences. Here are the median percent changes for the species in each category, with the number of species in parentheses:

Habitat	NM	non-NM
Forest	+20% (20)	+143% (16)
Edge/Mosaic	+32% (29)	+55% (30)
Open	-5% (7)	+43% (20)
Residential	+231% (4)	+69% (16)

In the first three habitats the neotropical migrants all show lower median changes; this reverses in the final category but there are very few neotropical migrant species that prefer residential habitats.

Looking at the average (rather than median) change, in most cases the pattern is similar with larger increases for the non-NM species in all cases:

Habitat	NM	non-NM
Forest	+43%	+208%
Edge/Mosaic	+13%	+35%
Open	-13%	+48%
Residential	+40%	+79%

In the case of the averages, statistics can be applied; the one pattern that is (highly) significant is the very large increase among the non-neotropical migrant forest species in comparison to all other categories. In the cases of the other three habitats, the smaller differences between the NM and non-NM trends are not quite statistically significant. It is interesting, though, that they all fall in the same direction.

Overall, the predominant pattern is large increases (an average of three-fold) in non-neotropical migrant forest birds, and a smaller general increase in other species (including the neotropical migrants). Of course a large number of these species do not show simple monotonic trends up or down over the entire 45 year history of the BBS; this is the topic for the next post.

Tennessee BBS index:
Introduction
1: Waterfowl to Herons
2: Vultures to Doves
3: Cuckoos to Woodpeckers
4: Flycatchers to Corvids
5: Larks to Wrens
6: Gnatcatchers to Waxwings
7: Wood Warblers
8: Towhees to Buntings
9: Icterids to House Sparrow
Ups and Downs
Habitats
Next: Inflection Points
Summary

Tennessee BBS: Ups and Downs

I have heard and read comments in the recent past suggesting that in another 50 years our North American avifauna will consist of a highly depauerate relict of exotics and a few generalists, with most of our native birds religated to isolated remainders if not outright extinction. If this doomsday future is going to come to pass, it certainly is not giving any hints of itself yet in Tennessee. These 45 years of Breeding Bird Survey data for Tennessee actually paint a picture of an avifauna that remains robust, diverse, and overwhelmingly native. Though there are some major red flags, and one native species that has been effectively extirpated in recent decades, the majority of Tennessee's breeding bird species have shown statistically significant increases over this time period. Exotics are not taking over the landscape; while there have been two new arrivals during the time frame, of the three other long establish invaders two have shown flat numbers while the third has declined rather drastically. The median for the 104 species that have sufficient data to establish a meaningful trend is a 66% increase between the 1966-1975 interval and the 2001-2011 period. This looks like a sign of Apocalypse Not rather than Apocalypse Now.

Downs

As mentioned, there are some "red flag" species showing ongoing major declines in numbers, and more that have experienced smaller drops. So to get to the bad news first, these 27 species showed statistically significant declines in BBS counts (biggest loosers listed first):

Bewick's Wren
Loggerhead Shrike
Golden-winged Warbler
Yellow Warbler
Northern Bobwhite
Common Nighthawk
Gray Catbird
House Sparrow
American Redstart
Eastern Meadowlark
Northern Flicker (Yellow-shafted Flicker)
Common Grackle
Whip-poor-will
Orchard Oriole
Cerulean Warbler
Chuck-will's-widow
Black-and-white Warbler
Chimney Swift
Belted Kingfisher
Prairie Warbler
Blue Jay
Yellow-breasted Chat
Wood Thrush
Common Yellowthroat
Brown Thrasher
Northern Mockingbird
Eastern Towhee

In this list and all the remaining analyses, I have not included species that occur only on small numbers of routes (generally high-elevation birds of far east Tennessee or wetland birds of far west Tennessee) or that were not recorded in enough years to display a meaningful trend. Many of these species are ones whose declines have attracted notice and concern, such as Bewick's Wren, Loggerhead Shrike, and Northern Bobwhite. But some were surprises to me. How much concern have you heard expressed about the disappearance of Northern Flickers as a breeding species in the region? Or Gray Catbirds? Or Orchard Orioles? It is interesting to note that the majority of these species are to a fairly large degree now dependent on human activities to create and maintain their habitats -- from the obvious (House Sparrows, Chimney Swifts) to the more subtle (Thrashers in early successional habitats, Belted Kingfishers on farm ponds). I will discuss habitat and landscape-level patterns in these trends more in a forthcoming post.

Holding Steady

These next 17 species showed trends that, though no identically equal to zero, where not significantly different from it. Again they are listed in order of their percentage change, even though these changes were not statistically significant:

Green Heron
Horned Lark
Ovenbird
Field Sparrow
Eastern Screech-Owl
Grasshopper Sparrow
Eastern Kingbird
Northern Cardinal
Kentucky Warbler
Mourning Dove
Summer Tanager
Red-winged Blackbird
European Starling
Rock Pigeon
Louisiana Waterthrush
Blue-winged Warbler
Great Horned Owl

This fairly short list is quite a mixed bag of species.

Ups

Finishing with the good news, the list of gainers is quite long. These 60 species showed statistically significant gains over the period (largest increases listed last):

Indigo Bunting
Eastern Wood-Pewee
Barn Swallow
Brown-headed Cowbird
American Crow
Killdeer
Great Crested Flycatcher
Acadian Flycatcher
Yellow-throated Vireo
Red-bellied Woodpecker
Worm-eating Warbler
Broad-winged Hawk
Downy Woodpecker
Dickcissel
White-eyed Vireo
Pileated Woodpecker
Hooded Warbler
Tufted Titmouse
Red-eyed Vireo
Chipping Sparrow
Song Sparrow
Barred Owl
Red-headed Woodpecker
Wood Duck
Scarlet Tanager
American Robin
Carolina Chickadee
Purple Martin
Baltimore Oriole
American Kestrel
Northern Rough-winged Swallow
Hairy Woodpecker
Eastern Bluebird
Eastern Phoebe
Carolina Wren
Blue Grosbeak
Yellow-throated Warbler
Blue-headed Vireo
Red-tailed Hawk
American Goldfinch
Ruby-throated Hummingbird
Blue-gray Gnatcatcher
Turkey Vulture
Sharp-shinned Hawk
Warbling Vireo
Pine Warbler
Black Vulture
White-breasted Nuthatch
Red-shouldered Hawk
House Wren
Cliff Swallow
Cooper's Hawk
Cedar Waxwing
Northern Parula
Wild Turkey
Great Blue Heron
Canada Goose
Tree Swallow
Eurasian Collared-Dove
House Finch

Though this is also a diverse list, two patterns jump out as you read through it. First, as I mentioned before, this list includes all of the diurnal birds of prey plus the two vultures. Even American Kestrels, subject of much concern regionally, showed a positive trend. Though it is just hypothesizing on my part, I have to suspect that this trend must be a combination of the effects of the DDT ban and reduced persecution because of better laws, law enforcement, and awareness. I know my own rural neighbors do not routinely shoot hawks; I suspect this would not have been the case 45 years ago!

The second pattern is a larger one which I will discuss more in the next post: Most of our forest birds are on this list. As Tennessee is principally a land of forests, both at present and in our ecological past, this pattern is the primary contributor to the overall message of good news for Tennessee's breeding birds coming out of these data. We still are home to extensive forests that are some of the most biodiverse temperate ecosystems on the planet, and our avifauna continues to strongly reflect this.

Tennessee BBS index:
Introduction
1: Waterfowl to Herons
2: Vultures to Doves
3: Cuckoos to Woodpeckers
4: Flycatchers to Corvids
5: Larks to Wrens
6: Gnatcatchers to Waxwings
7: Wood Warblers
8: Towhees to Buntings
9: Icterids to House Sparrow
Ups and Downs
Next: Habitats
Inflection Points
Summary

Tennessee BBS 9: Icterids to House Sparrow

Dickcissel

35 year change: +1.90 (+70%) ± 1.65

Numbers of Dickcissels tend to bounce up and down more than those of many other species, but the overall trend has been a modest and significant increase.


Red-winged Blackbird

35 year change: +3.57 (+11%) ± 6.26

The overall net change in Redwings for the BBS era is essentially zero. The graph suggests this was the end result of about 20 years of modest increases followed by a similar decline.


Eastern Meadowlark

35 year change: -26.50 (-61%) ± 3.68

Meadowlarks have declined steadily through the BBS era, with an overall drop of roughly threefold.


Common Grackle

35 year change: -55.30 (-58%) ± 18.82

Common Grackles have also dropped steadily and substantially through the period, again showing roughly a three-fold decline overall. At the beginning of the period this was by far the most abundant species on the BBS in Tennessee; it has now descended into the pack.


Brown-headed Cowbird

35 year change: +2.96 (+32%) ± 1.18

Cowbird numbers have shown a fairly modest but statistically significant increase over the BBS period.


Orchard Oriole

35 year change: -4.34 (-52%) ± 0.48

The more common of Tennessee's two oriole species has declined steadily, with recent numbers being less than half of those at the beginning of the survey.


Baltimore Oriole

35 year change: +0.39 (+125%) ± 0.17

Baltimore Orioles are less widely distributed, with the largest counts coming from the MAV routes in northwest Tennessee. Their numbers have shown a steady increase over the BBS era.


House Finch

35 year change: +4.56 ± 1.02

After first appearing in 1987 numbers of House Finches rose sharply over the next decade. Recent data suggest a possible decline from this peak, but more years are needed to assess whether or not this is real.


American Goldfinch

35 year change: +7.98 (+220%) ± 1.75

The overall change in Goldfinch numbers is a substantial increase of more than three-fold. This appears to be constructed from a low flat line through 1980 followed by a steady climb through 2000, then a modest decline in the last decade.


House Sparrow

35 year change: -23.80 (-70%) ± 5.29

House Sparrows have declined by nearly a factor of four since the beginning of the BBS. The rate of decline appears to have moderated in the last decade or so. It is interesting to note that this decline appears to have been underway before the arrival of the House Finch as a breeding species in 1987, but the steepest drop in House Sparrows does coincide with the time of most rapid increase in House Finches.

Tennessee BBS index:
Introduction
1: Waterfowl to Herons
2: Vultures to Doves
3: Cuckoos to Woodpeckers
4: Flycatchers to Corvids
5: Larks to Wrens
6: Gnatcatchers to Waxwings
7: Wood Warblers
8: Towhees to Buntings
9: Icterids to House Sparrow
Next: Ups and Downs
Habitats
Inflection Points
Summary

Tennessee BBS 8: Towhees to Buntings

Eastern Towhee

35 year change: -1.42 (-12%) ± 1.17

Towhee numbers have remained rather steady on Tennessee BBS routes. The small decline is statistically significant but is a minor change in context.


Chipping Sparrow

35 year change: +5.14 (+80%) ± 2.33

There seems to have been a "Great Sparrow Shift" around 1980 in Tennessee. Before this time, all the common species were showing rapid changes in abundance; when The Shift came their trends switched to the opposite direction or stabilized. In the case of the Chippie the initial trend was a substantial decline, which then shifted to a sustained increase. Overall the numbers rose significantly for the period.


Field Sparrow

35 year change: -3.05 (-18%) ± 3.45

For Field Sparrows, the Great Sparrow Shift was preceeded by a rapid decline amounting to a drop of over 50% in less than 10 years. After The Shift numbers gradually recovered, so that by the end of the period the net change was not significantly different from zero.


Lark Sparrow

35 year change: +0.01 (+8%) ± 0.07

Though they have been found on several different BBS routes, the data for Lark Sparrows are too limited to allow any trend to be seen.


Grasshopper Sparrow

35 year change: -0.06 (-6%) ± 0.45

This is another sparrow that shows a rapid decline of 50% or more in the beginning of the BBS period, followed by a recovery after The Great Sparrow Shift around 1980. The data are "bumpier" than those for some of the other sparrows, probably because of the loosely colonial nature of the species and the somewhat ephemeral nature of its habitat. Again, the net change for the total period was not significantly different than zero.


Song Sparrow

35 year change: +4.39 (+84%) ± 2.04

The Song Sparrow reverses the pattern shown by the other common sparrows. Its numbers rose rapidly in the early decades of the BBS, then stabilized after The Great Sparrow Shift. The overall increase for the BBS period was nearly two-fold.

Three other species of sparrows were tallied as presumed breeders on a few Tennessee BBS routes and on a very few occasions: Savannah, Vesper, and Bachman's. In all cases the data were far to skimpy to provide much information. Another species, Henslow's Sparrow, has been found in recent years to be highly local breeder at a number of sites spread over a large area of Tennessee. It has yet to be recorded on any BBS route in the state, however.


Summer Tanager

35 year change: +0.41 (+9%) ± 0.61

Summer Tanager numbers have remained stable over the BBS period, with no significant change.


Scarlet Tanager

35 year change: +1.46 (+111%) ± 0.42

In contrast, Scarlet Tanager numbers have more than doubled since the beginning of the BBS. Most of this increase happened before 1993, with fairly stable counts since then.


Northern Cardinal

35 year change: +1.34 (+4%) ± 2.84

Cardinals are abundant, ubiquitous, and show stable numbers over the BBS era.


Rose-breasted Grosbeak

35 year change: +0.02 (+628%) ± 0.02

This species has been tallied in quite variable numbers and on only a small number of BBS routes. Hence even a 628% increase is not statistically significant.


Blue Grosbeak

35 year change: +3.35 (+162%) ± 0.63

Blue Grosbeaks have increased steadily throughout the period, more than tripling in numbers from 1966 to 2010.


Indigo Bunting

35 year change: +4.374 (+11%) ± 3.08

Another of the most abundant and ubiquitous species on Tennessee BBS routes, Indigo Buntings have shown a statistically significant but fairly small increase. Overall their numbers appear to have been stable

Tennessee BBS index:
Introduction
1: Waterfowl to Herons
2: Vultures to Doves
3: Cuckoos to Woodpeckers
4: Flycatchers to Corvids
5: Larks to Wrens
6: Gnatcatchers to Waxwings
7: Wood Warblers
8: Towhees to Buntings
Next: 9: Icterids to House Sparrow
Ups and Downs
Habitats
Inflection Points
Summary