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USGS1989

Effects of organophosphorus insecticides on sage grouse in southeastern Idaho

Die-offs of sage grouse ( Centrocercus urophasianus ) were verified in southeastern Idaho in 1981. We captured 82 apparently healthy grouse to quantify the effects of organophosphorus insecticides (OP's) and other pesticides on sage grouse in sagebrush ( Artemisia spp.) bordering agricultural lands in July 1985 and 1986. Grouse were fitted with radio collars and tracked through part of each summer. At least 18% of 82 radio-tagged grouse in 1985-86 subsequently occupied fields at the time they were sprayed with OP insecticides dimethoate or methamidophos. Cholinesterase (ChE) assays of brains and residue analysis of crop contents indicated that 5 and 16% of the marked sample died from OP's in 1985 and 1986, respectively. Approximately 200 sage grouse were present in a block of alfalfa sprayed with dimethoate; 63 of these were later found dead and ChE activity in 43 brains suitable for assay were depressed >50%. Maximum residues in crop contents of dead grouse were 18 μg/g methamidophos and 30 μg/g dimethoate. Intoxicated or dead grouse were observed in or near 6 fields sprayed with dimethoate or methamidophos in 1985-86. Twenty of 31 intoxicated grouse radiotagged after being found in dimethoate-sprayed (1986) alfalfa died. Our study indicates that certain pesticides have the potential for adversely affecting grouse populations.

Idaho↗

USGS1990

Effects of visiting black brant nests on egg and nest survival

I used 2 methods to evaluate the effect of visiting black brant (Branta bernicla nigricans) nests on survival of whole nests and eggs in a single colony on the Yukon-Kuskokwim Delta, Alaska. The first technique regressed survival of nests or eggs during a time interval against interval length. Departure of the y-intercept from 1.0 estimated the short-term effect of the visit at the beginning of the interval. The y-intercepts (±95% CI) for whole nests and eggs during the egg laying period were 1.11 ± 0.31 and 1.06 ± 0.31, respectively. During incubation the same 2 parameters were 0.66 ± 0.31 and 0.66 ± 0.33. The regression method was, thus, imprecise and failed to discriminate among widely varying potential impacts of visitors. The second method involved visiting nests and then immediately revisiting them after pairs had returned to their territories. This method estimated loss of eggs as a result of displacement of territorial pairs during the first visit. Only 1 of 50 eggs was lost (n = 27 nests) as a result of visits during egg laying, whereas no eggs were lost (n = 225 eggs and 55 nests) owing to visits during the incubation period. I conclude that the regression approach is an imprecise tool for estimating visitor impact, but results from both methods indicate little effect of nest visitation under conditions existing on the colony I studied.

Alaska↗

USGS1990

Recent trends in counts of migrant hawks from northeastern North America

Using simple regression, pooled-sites route-regression, and nonparametric rank-trend analyses, we evaluated trends in counts of hawks migrating past 6 eastern hawk lookouts from 1972 to 1987. The indexing variable was the total count for a season. Bald eagle ( Haliaeetus leucocephalus ), peregrine falcon ( Falco peregrinus ), merlin ( F. columbarius ), osprey ( Pandion haliaetus ), and Cooper's hawk ( Accipiter cooperii ) counts increased using route-regression and nonparametric methods (P < 0.05). Northern harrier ( Circus cyaneus ) counts increased based on the nonparametric method (P < 0.01) but not the route-regression method (P > 0.10). We found no consistent trends (P > 0.10) in counts of sharp-shinned hawks ( A. striatus ), northern goshawks ( A. gentilis ) red-shouldered hawks ( Buteo lineatus) , red-tailed hawks ( B. jamaicensis ), rough-legged hawsk ( B. lagopus ), and American kestrels ( F. sparverius ). Broad-winged hawk ( B. platypterus ) counts declined (P < 0.05) based on the route-regression method. Empirical comparisons of our results with those for well-studied species such as the peregrine falcon, bald eagle, and osprey indicated agreement with nesting surveys. We suggest that counts of migrant hawks are a useful and economical method for detecting long-term trends in species across regions, particularly for species that otherwise cannot be easily surveyed.

Michigan, Minnesota, New Jersey, New York, Pennsyl↗

USGS1990

Winter use of douglas-fir forests by Blue Grouse in Colorado

We studied winter use of Douglas-fir ( Pseudotsuga menziesii ) forests by blue grouse ( Dendragapus obscurus ) from 1981 to 1983 at 2 study areas in northcentral Colorado. Comparisons of used and available stands indicated grouse were concentrated spatially, but there were no consistent differences related to basal area of tree species, conifer stem densities, and topography that were common to both areas. Blue grouse used dense (2,000 stems/ha) second growth (40-75 yr old), open to dense (200-1,900 stems/ha) mature (100-200 yr old), and open (<100 stems/ha) old-growth (200-600 yr old) stands. Stands used were composed of Douglas-fir alone or in association with subalpine fir ( Abies lasiocarpa ), Engelmann spruce ( Picea engelmannii ), lodgepole pine ( Pinus contorta ), limber pine ( P. flexilis ), Rocky Mountain juniper ( Juniperus scopulorum ), and quaking aspen ( Populus tremuloides ). Grouse used stands on mesic northern and eastern aspects, on xeric southern and western aspects, at elevations of 2,530-2,960 m, and on slopes of 1-45°. Preferential use (P < 0.05) of Douglas-fir trees occurred within stands that had an abundance of limber pine (use = availability) and subalpine fir (use < availability). Large Douglas-fir (20-90 cm dbh) were preferred (P < 0.05) within stands that had an abundance of smaller (≤15 cm dbh) trees. Both sexes used similar trees.

Colorado↗

USGS1990

Error in telemetry studies: Effects of animal movement on triangulation

We used Monte Carlo simulations to investigate the effects of animal movement on error of estimated animal locations derived from radio-telemetry triangulation of sequentially obtained bearings. Simulated movements of 0-534 m resulted in up to 10-fold increases in average location error but <10% decreases in location precision when observer-to-animal distances were <1,000 m. Location error and precision were minimally affected by censorship of poor locations with Chi-square goodness-of-fit tests. Location error caused by animal movement can only be eliminated by taking simultaneous bearings.