Wednesday, October 05, 2011

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:
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
Inflection Points


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