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At least 109 records · Page 6Linked to original sources

Survival rates and lifetime reproduction of breeding male Cooper’s Hawks in Wisconsin, 1980-2005

There are few published data on annual survival and no reports of lifetime reproduction for breeding Cooper's Hawks ( Accipiter cooperii ). Breeding males ( n = 105) in central and southeastern Wisconsin had an annual mortality rate of 19%, or a survival rate of 81% for birds ≤10 years of age. We did not detect significant differences in mortality rates between urban and rural habitats, nor between the earlier 13 years and later 13 years of this study. Male Cooper's Hawks produced from zero to 32 nestlings during their lifetimes. Body mass or size appeared unrelated to annual survivorship and lifetime reproduction, although lifetime reproduction was correlated strongly with longevity of breeding males. Fifteen of 66 males (23%) produced most (53%) of the nestlings. Our studies occurred in an area where breeding populations may be increasing with some of the highest reported productivity indices and nesting densities for this species. Habitat used for nesting on our Wisconsin study areas may be less important for survivorship and lifetime reproduction than acquisition of a nesting area in which a male will breed throughout his life.

Wisconsin

Home-range size and site tenacity of overwintering Le Conte's Sparrows in a fire managed prairie

We evaluated home-range size and site tenacity of Le Conte's Sparrows ( Ammodramus lecontii ) during winter 2002–2003 at Brazoria National Wildlife Refuge, Texas. Twenty-six wintering Le Conte's Sparrows were radiomarked in 1- and 2-year post-burn units, and monitored for ∼10 days. Additionally, 1-ha plots on each 1-, 2- and 3-year ( n = 15) post-burn units were flush-netted once monthly. Telemetry results indicated Le Conte's Sparrows were sedentary during winter with a 50% probability mean home-range of 2.41 ha (72% < 1 ha) and a 95% probability mean home range of 10.31 ha (44% < 1 ha and 55% < 1.5 ha). Home-range size did not differ between post-burn year 1 and 2 ( P = 0.227). Le Conte's Sparrows appeared to exhibit a behavioral response to flush-netting ( P < 0.001) with estimated capture probability of 0.462 and recapture probability of 0.056. Our findings suggest Le Conte's Sparrows remain fairly sedentary throughout the winter.

Texas

Influence of cover and food resource variation on postbreeding bird use of timber harvests with residual canopy trees

We investigated avian use of clearcuts and two-age harvests during the post-breeding period in 2006 in the central Appalachians, West Virginia, USA with an information-theoretic approach to model selection. Cover variables appeared to be most important; e.g., vegetative vertical complexity had a strong positive relation with capture rates of mature forest birds and molting adults, as well as physical condition which supports a predator-avoidance hypothesis for habitat use. Basal area was a poor predictor of captures; residual trees near nets tended to depress capture rates. Food variables best explained capture rates for some species groups (e.g., early-successional insectivores and granivores, mature forest nesting adults, molting birds), but post-breeding habitat quality was based primarily on vegetative cover. Habitat use may depend on the bird's physical condition and molt status, and we found evidence for age-specific differences which may impact survival. Our study suggests important links between post-breeding habitat quality, molt status, physical condition, and bird age, and indicates a variety of response variables (relative abundance, survival, body condition) should be measured to assess avian habitat quality during the post-breeding period.

West Virginia

Regional variation in diets of breeding Red-shouldered hawks

We collected data on breeding season diet composition of Red-shouldered Hawks (Buteo lineatus) in south Texas and compared these data, and those reported from studies elsewhere to examine large scale spatial variation in prey use in eastern North America. Red-shouldered Hawk diets aligned into two significantly different groups, which appear to correlate with latitude. The diets of Red-shouldered Hawks in group 1, which are of more northern latitudes, had significantly more mammalian prey and significantly less amphibian prey than those in group 2, which are at more southerly latitudes. Our meta-analysis demonstrated the dietary flexibility of Red-shouldered Hawks, which likely accounts for their broad distribution by exploiting regional variations in taxon-specific prey availability.

Wilson Journal of Ornithology

Temporal and spatial shifts in habitat use by Black Brant immediately following flightless molt

Each year thousands of Pacific Black Brant ( Branta bernicla nigricans ) undergo flightless wing molt in the Teshekpuk Lake Special Area (TLSA), Alaska, in two distinct habitats: inland, freshwater lakes and coastal, brackish wetlands. Brant lose body mass during wing molt and likely must add reserves upon regaining flight to help fuel their 2,500 km migration to autumn staging areas. We characterized movements and habitat use by Brant during post-molt (the period immediately following the recovery of flight) by (1) marking individual Brant with GPS (global positioning system) transmitters, and (2) conducting a series of replicate aerial surveys. Individuals molting in inland habitats promptly abandoned their molt wetland during the post-molt and moved into coastal habitats. Consequently, inland habitats were nearly deserted by early August when Brant had regained flight, a decrease of >5,000 individuals from the flightless period of early July. Conversely, coastal molting Brant largely remained in coastal habitats during the post-molt and many coastal wetlands were occupied by large flocks (>1,000 birds). Our results indicate that inland, freshwater wetlands were less suitable post-molt habitats for Brant, while coastal wetlands were preferred as they transitioned from flightless molt. The immediacy with which Brant vacated inland habitats upon regaining flight suggests that food may be limiting during molt and they are not selecting inland molt sites strictly for food resources, but rather a balance of factors including predator avoidance and acquisition of protein for feather growth. Our data clearly demonstrate that patterns of habitat use by Brant in the TLSA change over the course of the molt season, an important consideration for management of future resource development activities in this area.

Alaska

Effects of stop-level habitat change on cerulean warbler detections along breeding bird survey routes in the central appalachians

- We examined the effects of habitat change on Cerulean Warbler ( Dendroica cerulea) populations at stops along Breeding Bird Survey (BBS) routes in the central Appalachians. We used aerial photographs to compare early (1967/1971), middle (1982/1985), and late (2000/2003) periods and compared 1992 and 2001 National Land Cover Data (NLCD). Mean Cerulean Warbler detections per stop decreased at 68 BBS stops between the early (0.05) and middle (0.01) time periods and their distribution became more restricted (15 vs. 3% of stops), but the amount of deciduous/mixed forest increased. Mean detections at 240 stops decreased from the middle (0.09) to the late (0.06) time periods, but the deciduous/ mixed forest land cover and fragmentation metrics did not change. The amounts of deciduous/mixed forest, core forest area, and edge density in the NLCD analysis decreased from 1992 to 2001, whereas the amount of non-forest land cover increased. The number of Cerulean Warbler detections did not change (1992 = 0.08, 2001 = 0.10; P = 0.11). The lack of concordance between Cerulean Warbler detections and broad habitat features suggests that smaller, microhabitat features may be most important in affecting Cerulean Warbler breeding habitat suitability. Received 10 October 2009. Accepted 31 March 2011.

Appalachian Mountains

Cruise ships as a source of avian mortality during fall migration

A Avian mortality during fall migration has been studied at many anthropogenic structures, most of which share the common feature of bright lighting. An additional, unstudied source of avian mortality during fall migration is recreational cruise ships that are brightly lit throughout the night. I documented a single mortality event of eight Common Yellowthroats ( Geothlypis trichas ) on one ship during part of one night in fall 2003, but suggest this is a more wide-spread phenomenon. The advertised number of ship-nights for 50 cruise ships in the Caribbean Sea during fall migration in 2003 was 2,981. This may pose a significant, additional, anthropogenic source of mortality that warrants further investigation, particularly because impacts could be minimized if this source of avian mortality is recognized.

Wilson Journal of Ornithology

Wintering bird response to fall mowing of herbaceous buffers

Herbaceous buffers are strips of herbaceous vegetation planted between working agricultural land and streams or wetlands. Mowing is a common maintenance practice to control woody plants and noxious weeds in herbaceous buffers. Buffers enrolled in Maryland's Conservation Reserve Enhancement Program (CREP) cannot be mowed during the primary bird nesting season between 15 April and 15 August. Most mowing of buffers in Maryland occurs in late summer or fall, leaving the vegetation short until the following spring. We studied the response of wintering birds to fall mowing of buffers. We mowed one section to 10–15 cm in 13 buffers and kept another section unmowed. Ninety-two percent of birds detected in buffers were grassland or scrub-shrub species, and 98% of all birds detected were in unmowed buffers. Total bird abundance, species richness, and total avian conservation value were significantly greater in unmowed buffers, and Savannah Sparrows ( Passerculus sandwichensis ), Song Sparrows ( Melospiza melodia ), and White-throated Sparrows ( Zonotrichia albicollis ) were significantly more abundant in unmowed buffers. Wintering bird use of mowed buffers was less than in unmowed buffers. Leaving herbaceous buffers unmowed through winter will likely provide better habitat for wintering birds.

Maryland

Seasonal fecundity and source-sink status of shrub-nesting birds in a southwestern riparian corridor

Saltcedar ( Tamarix spp.) has increasingly dominated riparian floodplains relative to native forests in the southwestern U.S., but little is known about its impacts on avian productivity or population status. We monitored 86 Arizona Bell's Vireo ( Vireo bellii arizonae ), 147 Abert's Towhee ( Melozone aberti ), and 154 Yellow-breasted Chat ( Icteria virens ) nests to assess reproductive parameters in cottonwood-willow ( Populus-Salix ), saltcedar, and mesquite ( Prosopis spp.) stands along the San Pedro River, Arizona during 1999–2001. We also assessed source-sink status for each species in each vegetation type using field data combined with data from the literature. There were no significant differences in reproductive parameters between vegetation types for Abert's Towhee or Yellow-breasted Chat, although seasonal fecundity was quite low across vegetation types for the latter (0.75 ± 0.14; mean ± SE). Bell's Vireo had extremely low seasonal fecundity in saltcedar (0.10 ± 0.09) and significantly fewer fledglings per nest in saltcedar (0.09 ± 0.09) compared with cottonwood (1.07 ± 0.32). Point estimates of λ were substantially <1 for all three focal species in all habitats indicating the entire study area may be performing as a sink; 90% CI of included 1 only for Abert's Towhee across vegetation types and Bell's Vireo in cottonwood vegetation. These results are surprising given the San Pedro is considered to be one of the best remaining occurrences of lowland native riparian vegetation in the southwestern United States.

Arizona

Search behavior of arboreal insectivorous migrants at gulf coast stopover sites in spring

Search behavior of arboreal insectivorous migrants was studied at three stopover sites along the northern coast of the Gulf of Mexico during spring migrations, 1993–1995. We examined if search behavior was affected by phylogeny, or by environmental factors. A sequence of search movements (hop, flutter, or flight) in a foraging bout was recorded for each migrant encountered. Search rate, frequency, and distance of movements were calculated for each species. Search rate was positively correlated with proportion of hop, but negatively correlated to flight distance. Hop distance was positively correlated to tarsus length, as was flight distance to wing length for the 31 species of migrants. Cluster analysis indicated closely related species generally have similar foraging modes, which range from “sit-and-wait” of flycatchers to “widely foraging” of warblers. Migrants tended to use more hops in dense vegetation, but more flights in areas with sparse vegetation. Migrants also used more flights when foraging in mixed-species flocks and during periods of high migrant density. Logistic models indicated warblers were more influenced by environmental factors than vireos, possibly because warblers are near-perch searchers and more affected by these factors.

Wilson Journal of Ornithology

Interactions of raptors and Lesser Prairie-Chickens at leks in the Texas Southern High Plains

We examined behavioral interactions of raptors, Chihuahuan Ravens ( Corvus cryptoleucus ), and Lesser Prairie-Chickens ( Tympanuchus pallidicinctus ) at leks in the Texas Southern High Plains. Northern Harriers ( Circus cyaneus ) and Swainson's Hawks ( Buteo swainsoni ) were the most common raptors observed at leks. Only 15 of 61 (25%) raptor encounters at leks (0.09/hr) resulted in a capture attempt (0.02/hr). Mean (± SD) time for Lesser Prairie-Chickens to return to lekking behavior following a raptor encounter was 4.2 ± 5.5 min suggesting the disturbance had little influence on lekking behaviors. Lesser Prairie-Chickens engaged in different escape behaviors depending on raptor species and, generally, did not respond to ravens suggesting they are able to assess different predation risks. The raptors in our study area posed little predation risk to lekking prairie-chickens. Behavioral disturbance at leks appears minimal due to the lack of successful predation events, low raptor encounter rates, and short time to return to lekking behavior.

Texas

Grassland bird communtiy response to large wildfires

We studied breeding season communities of grassland birds on short-grass and mixed-grass prairie sites during the second and third breeding seasons following two large wildfires in March 2006 in the Texas panhandle, USA. There was an apparent temporary shift in avian community composition following the fires due to species-specific shifts associated with life-history traits and vegetation preferences. Species that prefer sparse vegetation and bare ground on short-grass sites, such as Horned Lark ( Eremophila alpestris ), benefited from wildfires, while others, such as Western Meadowlark ( Sturnella neglecta ), that prefer more dense vegetation, were negatively impacted. Mixed-grass sites had species-specific shifts in 2007, two breeding seasons after the fires; grassland bird communities on burned plots were similar by 2008 to those on unburned plots. Avian communities appeared to return to pre-burn levels within 3 years following wildfires. Many of the responses in our study of wildfire were similar to those reported following prescribed fires elsewhere. Prescribed fires appear to have similar effects on the avian community despite differences in intensity and environmental conditions during wildfires.

Wilson Journal of Ornithology

First record of interspecific breeding of Least Bell's Vireo and White-eyed Vireo

We provide the first known documentation of a male Least Bell's Vireo ( Vireo bellii pusillus ) breeding with a female White-eyed Vireo ( V. griseus ) and the first report of a White-eyed Vireo breeding in California at the San Luis Rey River, Oceanside, San Diego County. We discovered the pair building a nest on 12 May 2010. The female laid four eggs, and the pair successfully raised and fledged four nestlings. We collected DNA samples from each nestling and the female during the nestling stage and banded them with a numbered federal leg band for future identification. We obtained detailed nest measurements after fledging and monitored the territory for further nesting attempts. No additional nesting attempts were detected.

California

Effects of brood parasitism by brown-headed cowbirds may persist in the post fledging period

Brood parasitism by Brown-headed Cowbirds ( Molothrus ater ) typically decreases the number of host juveniles that fledge: however, little information exists regarding the effect of cowbird parasitism during the post-fledging period. We monitored 115 Ovenbird ( Seiurus aurocapilla ) nests in 2006&ndash;2008 in northcentral Minnesota, six of which were parasitized. We used radiotelemetry to monitor movements of 36 Ovenbird fledglings (nine additional fledglings depredated <24 hrs after fledging were excluded from the movement analysis) from non-parasitized nests and one fledgling from a parasitized nest. Clutch sizes and productivity were lower in parasitized Ovenbird nests than non-parasitized nests, similar to populations at other locations. The fledgling we tracked from a parasitized nest (in 2008) died after 26 days. It was the only fledgling in our study that died ( n = 20) with no sign of predation and an empty stomach. That fledgling took 12 days to travel >50 m from its nest and 25 days to travel >100 m from its nest. Fledglings from non-parasitized broods tracked for &ge;25 days during 2008 ( n = 16) took 4.1 &plusmn; 0.71 and 9.5 &plusmn; 1.14 days to travel the same distances. Our observations suggest that negative effects of brood parasitism may persist into the post-fledging period, possibly confirming observations of cowbird-only survival compiled from the literature.

Minnesota

Avian mortality associated with a volcanic gas seep at Kiska Island, Aleutian Islands, Alaska

We identified natural pits associated with avian mortality at the base of Kiska Volcano in the western Aleutian Islands, Alaska in 2007. Living, moribund, and dead birds were regularly found at low spots in a canyon between two lava flows during 2001&ndash;2006, but the phenomenon was attributed to natural trapping and starvation of fledgling seabirds (mostly Least Auklets, Aethia pusilla ) at a colony site with >1 million birds present. However, 302 birds of eight species, including passerines, were found dead at the site during 2007&ndash;2010, suggesting additional factors were involved. Most carcasses showed no signs of injury and concentrations of dead birds had accumulated in a few distinctive low pits in the canyon. Gas samples from these locations showed elevated CO 2 concentrations in late 2010. Analysis of carcasses indicated no evidence of blunt trauma or internal bleeding. Volcanic gases accumulating at these poorly ventilated sites may have caused the observed mortality, but are temporally variable. Most auklets breeding in the Aleutian Islands do so in recent lava flows that provide breeding habitat; our study documents a cost of this unusual habitat selection.

Alaska

Sexual selection and mating chronology of Lesser Prairie-Chickens

Little is known about mate selection and lek dynamics of Lesser Prairie-Chickens (Tympanuchus pallidicinctus). We collected data on male territory size and location on leks, behavior, and morphological characteristics and assessed the importance of these variables on male Lesser Prairie-Chicken mating success during spring 2008 and 2009 in the Texas Southern High Plains. We used discrete choice models and found that males that were less idle were chosen more often for mating. Our results also suggest that males with smaller territories obtained more copulations. Morphological characteristics were weaker predictors of male mating success. Peak female attendance at leks occurred during the 1-week interval starting 13 April during both years of study. Male prairie-chickens appear to make exploratory movements to, and from, leks early in the lekking season; 13 of 19 males banded early (23 Feb–13 Mar) in the lekking season departed the lek of capture and were not reobserved (11 yearlings, 2 adults). Thirty-three percent (range = 26–51%) of males on a lek mated (yearlings = 44%, adults = 20%) and males that were more active experienced greater mating success.

Wilson Journal of Ornithology

Behavioral activities of male Cerulean Warblers in relation to habitat characteristics

Activities of 29 male Cerulean Warblers ( Setophaga cerulea ) were quantified on two sites in West Virginia during May&ndash;June 2005. Singing and foraging were the most common of 11 observed behavioral activities (81.6%), while maintenance and mating behaviors were uncommonly observed. Male activity differed among vegetative strata ( P = 0.02) with lower- and mid-canopy strata used most often (70% of observations), especially for foraging, perching, and preening. The upper-canopy was used primarily for singing, particularly within core areas of territories and in association with canopy gaps. Foraging occurred more than expected outside of core areas. Males were associated with canopy gaps during 30% of observations, but the distribution of behavioral activities was not significantly related ( P = 0.06) to gap presence. Males used 23 different tree species for a variety of activities with oaks ( Quercus spp.) used most often on the xeric site and black cherry ( Prunus serotina ) and black locust ( Robinia pseudoacacia ) on the mesic site. Tree species used for singing differed between core and non-core areas ( P < 0.0001) but distribution of singing and foraging activity did not differ among tree species ( P = 0.13). Cerulean Warblers appear to be flexible in use of tree species. Their use of different canopy strata for different behavioral activities provides an explanation for the affinity this species exhibits for a vertically stratified forest canopy.

Wilson Journal of Ornithology

Provisioning of nestling Dickcissels in native warm-season grass field buffers

We used video cameras in 2008–2009 to record provisioning activities at Dickcissel (Spiza americana) nests in and around Conservation Reserve Program field buffers in north-central Mississippi, USA. We simultaneously observed foraging flight distances of parents. Provisioning rate (P = 0.412), biomass (P = 0.161), and foraging distance (P = 0.159) did not increase with nestling age. Parents delivered larger items to meet demand associated with older nestlings (P = 0.010–0.001). This suggests energetic costs of changes in prey selection were less than costs of increasing the number or distance of provisioning trips. Presence of male helpers increased provisioning rate (P < 0.001) but not biomass (P = 0.992) because males brought smaller prey items (P = 0.001–0.021). Presence of observers 30 m from the nest reduced provisioning rates (P = 0.005) and biomass delivered (P = 0.066). Lack of habitat effects for any aspect of provisioning suggests grass field buffers provided nestling food resources similar to surrounding habitats. Use of continuous video monitoring of nest activity allows well-concealed activities including provisioning and male helping to be directly observed and better quantified.

Mississippi