Rw. Hansen et Ld. Flake, ECOLOGICAL RELATIONSHIPS BETWEEN NESTING SWAINSONS AND RED-TAILED HAWKS IN SOUTHEASTERN IDAHO, The Journal of raptor research, 29(3), 1995, pp. 166-171
We compared reproductive success, nest site characteristics, and food
habits of nesting Swainson's hawks (Buteo swainsoni) and red-tailed ha
wks (B. jamaicensis) along the Big Lost River and Birch Creek on the I
daho National Engineering Laboratory, southeastern Idaho, from 1991-93
. Productivity was similar between specks. Twenty-four red-tailed hawk
nests produced 34 fledglings (1.4/attempt) while 17 Swainson's hawk n
ests produced 21 fledglings (1.2/attempt). Nest trees used by Swainson
's hawks were shorter, smaller, and more foliated than those used by r
ed-tailed hawks (P < 0.01). Swainson's hawk nest trees were more folia
ted than most trees along Birch Creek and the Big Lost River (P < 0.00
6). Red-tailed hawk nest trees were similar to available deciduous tre
es (>25% dead), but were taller (P = 0.001). Prey remains and castings
at nests (% frequency), indicated that Swainson's hawks preyed more c
ommonly on birds than red-tailed hawks while the latter more commonly
captured Lepus spp. and Sciuridae; Leporidae, including Lepus spp. and
Sylvilagus spp., made up over 60% of the estimated prey biomass for b
oth species. Riparian vegetation condition, notably the lack of narrow
leaf cottonwood (Populus angustifolia) survival and regeneration, appe
ared to be a major factor accounting for changes in hawk distribution
on the study area.