Wednesday, October 05, 2011

Tennessee BBS 9: Icterids to House Sparrow


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:
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
Inflection Points


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