Abundance
The 2003 Breeding Bird survey took place June 1 - June 25.
A total of 5,844 individual birds were recorded along the 13
survey routes. This is above the 1985-2002 average
of 4,375 birds/year (no surveys were conducted in 1992 or 1993).
Although bird numbers remained relatively
unchanged from the 2002 survey, drought conditions continued
during 2003 with higher than normal rainfall occurring in April
and lower than normal in May and June. Horned Larks and Meadow
Larks comprised more than 50% of all birds counted on the 2003
survey. Horned Larks are a dominant component of grassland
communities on the INL. The conversion from sagebrush to
grassland, due to large fires, has allowed this species to
increase in abundance. At the same time sagebrush obligate species
(e.g. Brewer’s Sparrow, Sage Sparrow, and Sage Thrasher) have
remained relatively stable but slightly decreased
The downward trend in the number of sagebrush
obligate species is consistent with the notion that sagebrush
habitat is being lost and may be negatively affecting these
populations of birds. This trend is very evident on the Big Lost
River route where in 2000 a wildfire consumed sagebrush on more
than 60% of the route. Before the 2000 fire more than 82% of the
vegetation on the route was dominated by sagebrush. After the
fire, only 22% of the route remained in sagebrush dominated
habitat. The figure below illustrates the dramatic increase in
Horned Lark numbers and the general decrease in the sagebrush
obligate species such as Brewer’s Sparrow, Sage Sparrow, and Sage
Thrasher. Although large expanses of sagebrush habitat remain of
the INL and fire is a natural part of the Snake River Plain
ecosystem, concern for the preservation of sagebrush habitat is
valid given that much of this habitat has been lost by conversion
to agriculture or development. At the very least, further
sagebrush habitat loss should continue to be monitored.
The high numbers of birds counted in 2003,
however, does not necessarily reflect large numbers of birds
counted among all taxa. Several species were at or below long-term
averages and a few species observed in six or more previous years
were absent in 2003, including Burrowing Owl, Bank Swallow, and
Blue-gray Gnatcatcher. Waterfowl counts at the INL were also low
due to the lack of water in the Big Lost River over the past 4
years. The Big Lost River, Sinks and Spreading Areas have not held
water since summer of 1999, thus reducing the number of birds that
would normally use these areas. The only waterfowl observed in
2003 were at the facility wastewater treatment ponds.
Several species
recorded in six or more previous years were not observed in 2002.
Burrowing
Owl
Bank Swallow
Blue-gray Gnatcatcher
Overall, 13 routes were surveyed on the INL
with approximately 446
± 162 total birds
counted per route. On the five remote routes the average number of
total birds observed was 595
±
77 with an average of 12
± 3 birds per
stop. The eight facility complex routes averaged 352
±126
total number of total birds observed with an average of 12
±
4 birds per stop (see above). The area surveyed at each stop on
remote routes is greater than the area surveyed at each stop on
the facility routes, so comparisons between facility and remote
routes are not directly comparable.
Overall, the five
most numerous species in order of abundance were:
Horned
Larks (Eremophilia alpestris)
Western
Meadowlarks (Sturnella neglecta)
Sage Sparrows (Amphispiza belli )
Brewer's
Sparrows (Spizella breweri)
Sage
Thrashers (Oreoscoptes montanus)
These species were the most frequently counted
species each year and usually comprise >70% of all birds detected.
Species
Richness
In 2003, a total of 67 species were
detected during the surveys. This is above the average of 56
±
8 recorded from 1985-2002. One new species for the BBS, the
Ring-necked Duck, was observed at the NRF wastewater pond,
increasing the total number of species detected along the routes
(1985-2003) to 114. In 2003, there were 24
±
5 species per route, with many similar species recorded along
remote routes (23 2) and facility routes (24
±
6). Facility routes had the fewest (N=15 @ PBF) and the greatest
(N=31 @ NRF & CFA) number of species observed. The number of
species observed on remote routes was similar with 20-26 species
observed on each route.
Habitat and species
assemblages
A limited assemblage of
breeding bird species that are typical of sagebrush steppe or
grassland communities within the Snake River Plain dominated
the avifauna of the INL. These species included native
species such as Sage Sparrow, Brewer’s Sparrow, Sage Thrasher
and Sage Grouse in the sagebrush, Rock Wrens within rocky
outcrops, Horned Larks and Vesper Sparrows in the grasslands,
and the ubiquitous Western Meadowlark, Mourning Dove,
Brown-headed Cowbird, Common Nighthawk, and Raven. Other less
common, but widespread species included the Common Poorwill,
Loggerhead Shrike, Grasshopper Sparrow, Lark Sparrow,
Great-horned Owl, Ferruginous Hawk, Red-tailed Hawk,
Swainson’s Hawk, and Prairie Falcon. There were also several
other bird species that are not usually found in sagebrush
steppe or grasslands and are principally relegated to a
variety of other distinct habitat types. For example, there
were species of birds that were found on the INL only in
junipers in patches near the buttes or along the base of the
Lemhi and Lost River Mountains. These species, including
Chipping Sparrow, and Gray Flycatcher, were counted at the
same sites almost every year and nowhere else. Waterfowl and
shorebirds were another group of birds that has limited
distribution on the INL, either in natural areas along the
Big Lost River (when it contains water) or in man-made ponds
near the facilities.
An additional array of bird
species that would not normally be observed in sagebrush
steppe or grassland habitats were found in altered or man-made
habitats of the INL. Permanent water, different food
resources, and buildings and planted trees for nest sites make
these areas suitable for species that would otherwise not be
located in this area. These species included House Finch, Barn
Swallow, American Robin, and Bullock’s Oriole. Most of these
species are native to well-watered areas within the Snake
River Plain and/or surrounding mountains, but the facilities
provide habitat for these species as well as non-natives such
as the Rock Dove, House Sparrow, and European Starling.
Finally, there were birds, such as the Brewer’s Blackbird,
Black-billed Magpie, and Say’s Phoebe that were found both
near the facilities and in remote areas.
Species of
special concern
State and Federal species of special
concern observed during the 2003 census included:
Long-billed Curlew (N = 1)
Ferruginous Hawk (N = 13)
Swainson’s Hawk (N = 3
Loggerhead Shrike (N = 39)
Greater Sage Grouse (N = 19)
The Burrowing Owl has not been observed
since 2000. The sagebrush steppe habitat on the INL
continues to support species of birds that are low or
declining in number throughout the Intermountain West.
