Tuesday, October 11, 2011

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:
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
Inflection Points


At 4:47 AM, Anonymous Carole Gobert said...

Fascinating stuff. An impressive analysis.

At 5:07 PM, Anonymous Anonymous said...

What do you make of the recent video release of the Imperial Woodpecker? Cornell published some interesting data on its flight characteristics.

At 6:26 PM, Blogger Bill Pulliam said...

Working on it -- posts will be forthcoming, stay tuned. Probably in a week or so.

At 7:09 PM, Anonymous Anonymous said...

Bill, this strikes me (a birder but by no means trained or ardent these days) as valuable work. I hope birders and researchers in Tennessee realize the good of what you've done. We could use something like this in Michigan, assuming there isn't such a study yet.


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