Western Birds Journal

Volume 55, No. 1

Published January 1, 2024

Issue description

Volume 55, number 1 of Western Birds, published 2024

Articles

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    DANA J. BOVE, HOLLY A. ANDERSON, MATTHEW A. SMITH, THEO A. KUHN (Author)

    NESTING BALD EAGLE POPULATION NUMBERS, DENSITY, TERRITORIAL RESOURCES, AND RELATIONSHIP TO HUMAN DEVELOPMENT IN NORTHERN COLORADO’S FRONT RANGE

    To better understand the population of the Bald Eagle (Haliaeetus leucocephalus) nesting along northern Colorado’s Front Range, from 2016 to 2022 we studied 86 occupied nests within an area of 20,586 km². From 2017 to 2020, 279 juveniles fledged from 237 nesting attempts in a smaller, main nest-study area with 68 nests. The nests’ success over these four years ranged from 52 to 70%, and their productivity varied from 1.1 to 1.3. The average nearest-nest distances for three discrete areas in the Front Range (5.03 to 7.26 km) are at least 2.8 to 4.0 times greater than these distances in four nesting populations in wetter regions but shorter than distances observed between nests in drier Arizona. In our study area the coverage of buildings within 400 m of Bald Eagle nests is relatively low by comparison to the coverage around randomly selected points, averaging 1344 m²; for 63% of the nests this coverage was less than 800 m². We classified the 86 nest territories into eight categories that describe the dominant resource habitat and predicts the eagles’ reliance on Black-tailed Prairie Dogs (Cynomys ludovicianus) versus fish as prey. Predation on fish was predicted to be dominant at 51% (n = 44) of the nests, predation on prairie dogs at 32% (n = 28).

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    DAVID F. DeSANTE, RICHARD A. ERICKSON, GERARDO MARRÓN, PETER PYLE (Author)

    DAVID F. DeSANTE’S BIRDS OF CABO SAN LUCAS, FALL 1968: A HISTORIC ACCOUNT

    In preparation for his doctoral studies at Stanford University, the late David F. DeSante spent the fall of 1968 studying migratory landbirds at Cabo San Lucas. Although his hopes to capture numerous vagrant warblers were not met, he amassed an impressive list of distributional records for the Baja California Peninsula at a time when few ornithologists were working there. Among these were peninsular firsts for the Ring-necked Duck (Aythya collaris), Broad-billed Hummingbird (Cynanthus latirostris), Broad-winged Hawk (Buteo platypterus), Bobolink (Dolichonyx oryzivorus), and Painted Bunting (Passerina ciris). Another six species, and one subspecies, were found for the first time in Baja California Sur. Venturing away from the immediate confines of Cabo San Lucas, DeSante established the first peninsular record of the Gray-headed Junco (Junco hyemalis caniceps) and first state records for another five species and one subspecies. Although many of these records have been reported previously, the junior authors believe it is appropriate to synthesize them more completely with current context, in Dave’s honor.

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    PETER J. OLSOY, KATIE J. SORENSON (Author)

    FIRST RECORD OF TRICOLORED BLACKBIRDS IN IDAHO

    Over 99% of Tricolored Blackbirds (Agelaius tricolor) occur in California. However, small populations persist in Oregon, Washington, Nevada, and Baja California. Loss of wetlands that historically served as foraging and breeding habitat has led to their increasing use of agricultural landscapes including silage fields and cattle feedlots. Here we provide the first documentation of the Tricolored Blackbird in Idaho (26 March–13 May and 3 November–16 December 2023), of up to 30 birds observed at five different locations associated with cattle feedlots, each 10–15 km apart, in Payette and Gem counties. Seven observations included recordings of vocalizations (3-23 April and 14 December 2023), largely coinciding with the final observations at each location, presumably before dispersal to breeding grounds. We consider three hypotheses to explain the apparently sudden occurrence of these birds, including their return to some of the same sites in November 2023: (1) a continued pattern of range expansion due to climate change; (2) an undetected long-term population due to low survey effort; or (3) a large-scale movement in response to flooding and extreme weather in the traditional range. We encourage continued monitoring and surveying of these locations in the coming years and surveying for both new wintering locations and for evidence of the Tricolored Blackbird breeding in Idaho.

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    JOSEPH C. ORTEGA, CATHERINE P. ORTEGA (Author)

    FACTORS INFLUENCING SURVIVAL OF BLACK-CHINNED HUMMINGBIRD NESTS IN SOUTHWEST COLORADO

    We estimated survival of Black-chinned Hummingbird (Archilochus alexandri) nests in southwest Colorado in 1998, 2001, and 2004 by means of models generated in program Mark. The best supported, and parsimonious, model suggested nest age (i.e., time since the nest was initiated) as the most important variable in indicating nest survival; daily survival rates of nests with eggs were lower than those of nests with nestlings. Substrate type was a second covariate that had some support in describing nest survival. Nests in Gambel oak (Quercus gambelii) or narrow-leaf cottonwood (Populus angustifolia) had greater daily survival rates than did those built in other substrates. No other ecological covariates were strongly supported in explaining nest survival. Of the 24 nests studied, 10 were successful, fledging an average of 1.7 (standard error 0.14) chicks.

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    ROBERT L. SCHER (Author)

    SECOND PREBASIC MOLT OF A BLACK-HEADED GULL AT ANCHORAGE, ALASKA

    A second-cycle Black-headed Gull (Chroicocephalus ridibundus), a rare to casual visitor in western North America, remained at Anchorage, Alaska, from 16 July through 17 September 2023, providing a unique opportunity to track and document most stages of its second prebasic molt into definitive (adult) basic plumage. I estimated that the Anchorage bird required approximately 3 to 3.5 months (early/mid-June through late September) to complete the molt of its primaries. This is notably longer than the "average" 2.5 months stated for second-cycle Black-headed Gulls in several publications, but consistent with the duration and calendar limits reported by others for the entire species (mid-May/June through September). The start and duration of retraction molt relative to the stage of primary molt closely matched that described for gulls in general, and specifically for definitive Bonaparte’s (C. philadelphia) and Western (Larus occidentalis) gulls. When first observed in mid-July, the Anchorage bird had a white tail, as in definitive plumage, a trait infrequent in first-cycle Black-headed Gulls; then it molted the tail again through August. Although Black-headed Gulls occurring in western North America have been presumed to originate from eastern Asia, the timing of the Anchorage bird’s primary molt closely matched that published for second-cycle Black-headed Gulls in Europe, which has reported to be earlier—though molt schedules of Charadriiformes at the population level are highly variable.

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    SIERRA R. GLASSMAN, EMILY Y BANNO (Author)

    AMERICAN CROW CRACKS OPEN BIVALVE VIA AUTOMOBILE

    There have been many observations of corvids placing a hard-shelled food item onto a roadway, then consuming the food exposed when a passing automobile crushes the shell. However, it has been debated whether corvids perform this behavior intentionally. Our observation of an American Crow (Corvus brachyrhynchos) placing a bivalve on a road, then eating the meat exposed when the shell was run over, supports the idea that corvids intentionally use cars to crack shelled foods.