Western Birds Journal

Volume 54, No. 3

Published July 1, 2023

Issue description

Volume 54, number 3 of Western Birds, published 2023

Articles

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    LORI HARGROVE, PHILIP UNITT, GERARDO MARRÓN, TONATIUH GAONA-MELO , GORGONIO RUIZ-CAMPOS (Author)

    BREEDING STATUS OF THE GRAY VIREO ON THE BAJA CALIFORNIA PENINSULA

     Most of the breeding range of the gray vireo (Vireo vicinior) lies within the southwestern United States, where the population is sparse, patchy, and declining. But the species also breeds in Baja California, Mexico, where its status has not been assessed. to rectify this, in 2021 and 2022 we surveyed four mountain ranges where the gray vireo is known or might be expected. in the northernmost, the Sierra Juárez, we located 43 territories—an abundance strikingly greater than just across the border in Upper California. territories were in both treeless chaparral dominated by chamise (Adenostoma fasciculatum) and redshank (A. sparsifolium), and in the extensive pinyon woodland. in the Sierra San Pedro Mártir, all 71 territories located were in Adenostoma-dominated chaparral. extrapolation of the densities observed in these two ranges over the extent of suitable habitat implies the population of the gray vireo in Baja California should be over 10,000 individuals. Confirmed by audio recording, one sighting from the Sierra de Ulloa overlooking ensenada suggests a still wider distribution in Baja California. isolated stands of chaparral grow south of the gray vireo’s previously reported breeding range, on the Sierra La asamblea. But our reconnaissance of it revealed no gray vireos. Survey of the Sierra San Francisco in the center of the peninsula, 3–9 april, revealed only 3 gray vireos, all in winter habitat containing Bursera microphylla. therefore two molting specimens collected in the Sierra San Francisco in october 1997 imply that some individuals molt in the winter range, not a southward extension of the breeding range. Despite Baja California representing only a small part of the gray vireo’s breeding range spatially, it contributes disproportionately to the species’ population and therefore conservation.

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    DAVID M. GOODWARD, RUDY A. DIAZ (Author)

    TRICOLORED BLACKBIRDS’ RELIANCE ON INSECTS FROM DAIRIES

     The Tricolored Blackbird has been in a severe population decline due to habitat loss and other factors. It is now heavily dependent on agricultural landscapes such as hay fields for foraging and grain fields for nesting. Dairies are known to provide a concentrated food source throughout the year in the form of grain gleaned from cattle feed. For nesting, however, Tricolored Blackbirds require large quantities of insects for their young. A colony of Tricolored Blackbirds in the San Jacinto Valley, Riverside County, in southern California, fed their young large numbers of house flies from nearby dairy-cattle yards, as well as drone fly larvae from dairy-effluent ponds. At this colony, 67% of the nestlings’ food came from the dairy and another 13% from the adjacent hay fields. Most other insects came from irrigated weedy growth adjacent to wetlands. Such an intense reliance on dairies is risky for the blackbirds as urbanization is displacing the dairy industry in the San Jacinto Valley and many other areas of California. Another potential risk to the blackbirds is the use of pesticides at dairies for fly control. Further research is recommended to determine if this utilization of flies from dairies is widespread in California. Research is also needed to quantify the decrease of insects in drought-stricken landscapes and how this may affect the Tricolored Blackbird’s reproductive success.

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    BRIAN G. TAVERNIA (Author)

    PATCH AREA CANNOT PREDICT SPECIES RICHNESS OF GRASSLAND BIRDS IN COLORADO’S FRONT RANGE

     Birds breeding in grassland have declined steeply over the last 50 years, and green-space systems in Colorado’s urbanizing Front range have not maintained all grassland bird species the area originally supported. Patch area affects the species richness of urban green spaces, and researchers have suggested that protecting or enlarging green spaces should be effective ways to maximize richness and mitigate species loss. in the Front range, protection of urban green space is expensive, conservation budgets are limited, and tools are needed to guide strategic protection decisions. Front range planners use patch area as a criterion to prioritize grassland conservation, but the explanatory and predictive powers of patch area have not been comprehensively assessed. Using eBird community science data, i found that log-transformed grassland patch area was positively associated with the species richness of grassland birds and explained a large portion of its variance. However, 95% simultaneous prediction intervals for species richness were wide, and those of the smallest and largest patches examined overlapped. Thus the model cannot precisely predict a number of species, and it should not be used to quantitatively evaluate the expected return on investment from financial allocations to protect or enlarge grassland patches. nonetheless, the model’s explanatory power supports the use of grassland patch area as a general principle guiding conservation of grassland birds. Planners should consider it among a suite of other habitat characteristics and prioritize large, regularly shaped grassland patches situated close to other grassland patches and with limited nearby forest cover and urban development.

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    NOLAN M. CLEMENTS, JAMES R. TIETZ (Author)

    FIRST RECORD OF THE SMALL-BILLED ELAENIA (ELAENIA PARVIROSTRIS) FOR WESTERN NORTH AMERICA

     The Small-billed Elaenia (Elaenia parvirostris) is a small flycatcher common on the Atlantic slope of South America. The species breeds below 1000 m elevation in open woodlands, gardens, and forest edges from southern Brazil to northeastern Argentina and migrates north to spend the nonbreeding season in the northern Amazon Basin. Since 2012, it has been documented as a vagrant to North America, with four records from the United States and Canada to date. On the basis of one photographed on Southeast Farallon Island on 4 September 2022, we record a fifth Small-billed Elaenia in North America, a first for California and the Pacific coast. Its novelty notwithstanding, it represents an outlier of an established pattern of vagrancy of tyrant flycatchers from South America reaching North America via overshooting or reverse migration.

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    CEDAR MATHERS-WINN, DEBBIE LEICK, KATE STONE (Author)

    A METHOD FOR DISTINGUISHING FLIGHT CALLS OF SEVERAL WESTERN BIRDS

     Billions of birds migrate under the cover of darkness, making them difficult to detect except by calls given in flight. Recording and identifying these calls can document the species of birds passing overhead and provide an index to their numbers. However, flight calls of some species are quite similar and difficult to tell apart. We investigated a method of identifying calls of several species whose calls are difficult to distinguish: the Solitary (Tringa solitaria) versus Spotted (Actitis macularius) Sandpipers and the White-crowned (Zonotrichia leucophrys) versus Brewer’s (Spizella breweri) and Clay-colored (S. pallida) Sparrows. We generated audiospectrograms of diurnal flight calls of known identity and inspected these for qualitative criteria by which the calls could be distinguished without the need for measurements or statistical software. We then tested the efficacy of these criteria on a new set of previously identified flight calls. Consideration of multiple criteria allowed identification of ~50% of one of the two types of sandpiper calls analyzed and ~60% of the sparrow calls, so a significant fraction remained unidentifiable by this method. Nevertheless, we hope researchers and sound recordists will apply this guide to improve our understanding of migration throughout western North America. We also encourage recordists to contribute additional visually verified recordings to allow us or others to perform similar tests on other species and species groups.

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    PETER ADRIAENS, AMAR AYYASH, MARS MUUSSE (Author)

    EXTENSIVE PREALTERNATE MOLTS IN PERUVIAN KELP GULLS

     According to current literature, the Kelp Gull (Larus dominicanus) matures at the same rate and molts according to the same patterns as most other large gulls, such as the American herring (L. argentatus smithsonianus) and Western (L. occidentalis). the Kelp Gull, however, is widespread through the southern hemisphere, with separate populations occupying no fewer than four different climate zones and breeding at different times of the year; the molt of some of those populations appears to have not been studied yet. here we demonstrate that many immature Kelp Gulls of the Peruvian population undergo much more extensive first and second prealternate molts than has been known so far and achieve an adult-like plumage aspect in as soon as 2.5 years rather than the usual 4. in these respects, these Kelp Gulls recall the yellow-footed Gull (L. livens) or subspecies heuglini and fuscus of the Lesser Black-backed Gull (L. fuscus).

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    D. JULIAN TATTONI (Author)

    AN ECCENTRIC PREFORMATIVE MOLT WITH INCOMPLETE REPLACEMENT OF PRIMARY COVERTS IN A DARK-EYED JUNCO

     Though the Dark-eyed Junco has not been reported to replace any juvenile primaries during its preformative molt, one first-cycle bird captured at Stanford, California, in november 2022 had replaced all its remiges but the three innermost primaries. Thus it followed the eccentric pattern more frequently seen in other sparrows, wrens, and some tyrant flycatchers. This novel pattern may be an adaptation to the urban habitats that the junco has recently colonized.