Thursday, September 29, 2011

Tennessee BBS 2: Vultures to Doves

Vultures, Hawks, etc.

There are 11 species of vultures and diurnal birds of prey with enough BBS data for Tennessee to make meaingful graphs. All 11 of them seem to be telling the same story:

35 year change: +2.38 (+661%) ± 0.63

35 year change: +3.76 (+295%) ± 0.73

35 year change: +0.04 (+1685%) ± 0.03

35 year change: +0.06 (+2206%) ± 0.02

35 year change: +0.0012 ± 0.0011

35 year change: +0.03 (+354%) ± 0.02

35 year change: +0.17 (+841%) ± 0.07

35 year change: +0.73 (+771%) ± 0.17

35 year change: +0.12 (+70%) ± 0.10

35 year change: +0.71 (+213%) ± 0.23

35 year change: +0.44 (+130%) ± 0.29

All of these species have shown a statistically significant increase in this time, even the ones with limited data. Most of these increases have been quite large, with a median growth of nearly 8-fold. This may be an effect of the DDT ban, reduced persecution, increased food availability, or active restoration programs; it is probably a result of all these as well as other factors. Whatever the reasons, it is clear that birds of prey have had some good decades since the 1960s. Some of these increases appear to have stabilized while others seem to be continuing. Hopefully none of them will turn around anytime soon.


35 year change: +1.35 (+47%) ± 0.90

Only one species of shorebird has a meaningful amount of BBS data for Tennessee. There are a few scattered records for Spotted Sandpipers and American Woodcock, but not enough to provide any real information. The statistically significant increase in Killdeer numbers all happened in the first decade of the BBS. Numbers have been relatively stable since then.

Least Tern

35 year change: +0.16 (+173%) ± 0.31

Though the graph gives the impression of a substantial presence of Least Terns on Tennessee BBS routes, in reality virtually all these birds are found on one single route, PawPaw in Lake County. A single individual was also found one time a bit farther north on the Tiptonville route, also in Lake County. Hence these data are less meaningful than they might appear. Because of the large year-to-year variation, the nearly three-fold increase in the average count over the course of the survey is not statistically significant.

Rock Pigeon

35 year change: +0.74 (+21%) ± 1.22

Though there are apparent ups and downs, overall the counts or Rock Pigeons appear stable. As they tend to occur in clumps and flocks near suitable bridges, silos, and other structures, small local effects (e.g. bridge construction) can make large bumps.

Eurasian Collared-Dove

35 year change: +0.31 ± 0.17

A recent arrival in Tennessee, this alien species first turned up on a Tennessee BBS route in 1999. Numbers quickly rose; whether they will continue to rise or have begun to stabilize remains to be seen.

Mourning Dove

35 year change: +1.81 (+6%) ± 4.28

Abundant and ubiquitous, Mourning Dove counts have remained remarkably steady through the entire BBS era. The tiny increase in average counts is statistically insignificant.

Tennessee BBS index:
1: Waterfowl to Herons
2: Vultures to Doves
Next: 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


Post a Comment

<< Home

Site Meter