[CT Birds] Tennessee Warbler question
pcianfaglione at hotmail.com
Mon Oct 24 09:44:48 EDT 2011
I don't know if this answers your question about why Connecticut is seeing more Tennessee Warblers this fall, but the overall population is still quite large. Here is some info from the pages of Birds Of North America Online, hope this helps;
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One of the most abundant boreal warblers, although breeding densities are irregular and fluctuate in response to epidemics of spruce budworm. In n. Ontario, populations increased by a factor of 9 over 4 yr (1979–1982), then decreased by 30% the following year. During this period, densities ranged from 75- to 610 pairs/km2 in mature forest, while in cutover areas <10 yr of age, densities increased from 0 to 336 pairs/km2 (Cadman et al. 1987). Breeding densities markedly higher in e. Canada (mean 159.8 males/100 ha, n = 84 plots sampled from Ontario eastward) than in w. Canada, with respective means of 159.8 males/100 ha (n = 84 plots sampled from Ontario eastward) and 48.9 males/100 ha, (n = 24 plots sampled from Manitoba westward; Erskine 1971, 1972, 1980, 1984). Highest densities recorded from 10- to 25-yr-old regenerating cutover boreal conifer forests in Ontario: (mean of 7 plots = 528.6 males/100 ha, (range 217–794, n = 7 plots; Welsh and Fillman 1980). Recorded as most abundant species on 9 of 21 (43%) Ontario census plots and 38 of 51 (75%) Quebec plots (Erskine 1971, 1972, 1980, 1984). Continent-wide Breeding Bird Survey (BBS) data show area of highest densities in Quebec north of Gulf of St. Lawrence, although highest individual route densities, recorded in Northwest Territories and New Brunswick, were 82.3 and 54.2 birds/route, respectively (Price et al. 1995). Densities generally higher in budworm-infested forests than in forests with few or no budworm (Erskine 1977).
No information on densities from wintering grounds. During migration in Illinois, maximum spring densities of 246 birds/40.5 ha in mature upland forest, maximum fall densities of 255 birds/40.5 ha in forest edge habitats (Graber et al. 1983).
Current population levels probably exceed historical nineteenth-century levels, because of exploitation of spruce budworm outbreaks and occupancy of successional habitats following logging operations. Long-term (1966–1995) BBS data show nonsignificant increase in U.S. and Canada (Sauer et al. 1997). From 1966 to 1979, continental populations increased significantly, presumably in response to widespread epidemics of spruce budworm; from 1980 to 1995, significant overall decline occurred, coinciding with diminished budworm outbreaks. No consistent geographic patterns in BBS 30-yr trends. New Brunswick and Newfoundland showed significant declines; Nova Scotia a significant increase; Maine, Quebec, Ontario, and British Columbia nonsignificant increases; Alberta no change. During 1980–1995, Maine and all Canadian provinces showed declines; more pronounced in West than East. In Fundy National Park, New Brunswick, censuses in 1992 detected only 2% (16) of the 722 birds encountered in 1979, primarily because of collapse of budworm populations (Christie 1993).
Long-term migration banding data showed nonsignificant decreases in Ontario over 28 yr (1961–1988; Hussell et al. 1992) and in Massachusetts over 19 yr (1970–1988; Hagan et al. 1992). At both sites, shorter-term fluctuations corresponded closely to cycles of spruce budworm outbreaks in e. North America. Forty years (1950–1989) of migration count data from Massachusetts showed significant overall increase, but nonsignificant over shorter 10-yr (1980–1989) and 20-yr (1970–1989) periods; mid-1970s peak in abundance coincided with known budworm outbreak (Hill and Hagan 1991).
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