Western Birds Journal

Volume 40, No. 4

Published October 1, 2009

Issue description

Volume 40, number 4 of Western Birds, published 2009

Articles

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    DANIEL A. AIROLA, DAN KOPP (Author)

    RECENT PURPLE MARTIN DECLINES IN THE SACRAMENTO REGION OF CALIFORNIA: RECOVERY IMPLICATIONS

    We monitored the Purple Martins (Progne subis) breeding in the Sacramento region, California, in 2008 and 2009, following similar monitoring from 2002 to 2007. This bridge-nesting population is the last remnant of the formerly widespread Central Valley population. All 11 colonies occupied in 2007 remained active in 2008, but the number of occupied colonies declined to 9 in 2009. From 2007 to 2009 the number of breeding pairs declined by 34%, from 106 to 70. Since 2004, the population has declined by 60% (103 pairs), and the annual rate of decline has increased. Probability calculations suggest the decline has been caused by factors other than chance fluctuation. If the decline continues at its current rate, the population will be extirpated within 22 years. Causes of the decline are unknown, but our previous studies have implicated mortality during the breeding season from vehicle collisions. Sacramento-area populations also are threatened by disturbance from a variety of construction projects and land-use changes that may affect habitat suitability. Recent losses in Sacramento represent a 6–11% decline in California’s estimated Purple Martin population. Increased effort is needed to stabilize the Sacramento population, which would serve as the likely source for any future recovery within the Central Valley.

     
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    EVELYN L. BULL, CHARLES T. COLLINS (Author)

    FURTHER DECLINE IN NEST-BOX USE BY VAUX’S SWIFTS IN NORTHEASTERN OREGON

    Populations of the Vaux’s Swift (Chaetura vauxi), a species of conservation concern, are declining in the Pacific Northwest. We compared the number of swifts nesting in boxes 2007–2008 to those nesting in the same boxes 1999–2002 to determine if numbers had changed. There were 51 nest attempts in the earlier 4-year period but only two to five nest attempts in the later 2-year period, an average decline of 72% in nest-box use. The cause of the decline is unknown. Northern Flying Squirrels (Glaucomys sabrina), Bushy-tailed Woodrats (Neotoma cinerea), and Red Squirrels (Tamiasciurus hudsonicus) usurped some of the nest boxes. Seven of seven swifts tested negative for the antibodies of West Nile virus. Conservation measures that protect existing nest and roost sites and create additional nesting sites (nest boxes and chimneys) would help ensure that habitat is not limiting Vaux’s Swift populations.

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    KATHY C. MOLINA, MARK A. RICCA, A. KEITH MILES, CHRISTIAN SCHONEMAN (Author)

    USE OF A NESTING PLATFORM BY GULL-BILLED TERNS AND BLACK SKIMMERS AT THE SALTON SEA, CALIFORNIA

    In 2006, we constructed an elevated nesting platform at the Salton Sea, California, and monitored its use by Gull-billed Terns and Black Skimmers over three subsequent breeding seasons. Black Skimmers were the first to colonize the platform with a total of five nests in 2006. In 2007 Gull-billed Terns colonized the platform with a total of 28 nests and the number of Black Skimmer nests increased to 20. Neither species nested on the platform in 2008. Low success for both species was probably influenced by at least two factors. First, when both species nested on the platform, nest densities were higher than is typical of their colonies on larger, earthen islands, and colony success may have been reduced by overcrowding. Second, lack of access to water may have reduced chicks’ ability to thermoregulate effectively in the hot environment of the Salton Sea. Refinements to the size, design, and location of artificial nesting habitats are necessary to enhance productivity of colonial ground-nesting birds at the Salton Sea successfully.

     
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    JUAN-PABLO GALLO-REYNOSO, ANA-LUISA FIGUEROA-CARRANZA (Author)

    BIRDS OF PREY AND THE BAND-TAILED PIGEON ON ISLA GUADALUPE, MEXICO

    We noted eight species of birds of prey at Isla Guadalupe during ten visits from 1991 to 2003. The most abundant species was the Burrowing Owl (Athene cunicularia), found throughout the island; second most numerous was the American Kestrel (Falco sparverius), widespread but uncommon. The frequency of the kestrel paralleled the population of mice, peaking 1992, a year of El Niño. We observed the Red-tailed Hawk (Buteo jamaicensis), Osprey (Pandion haliaetus), and Peregrine Falcon (Falco peregrinus) two or three times each, the Prairie Falcon (F. mexicanus) once. Our records of the Northern Harrier (Circus cyaneus) and Band-tailed Pigeon (Patagioenas fasciata) are the first for Isla Guadalupe.

     
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    GRETA M. WENGERT, MOURAD W. GABRIEL, RYAN L. MATHIS, THOMAS HUGHES (Author)

    FOOD HABITS OF WILD TURKEYS IN NATIONAL FORESTS OF NORTHERN CALIFORNIA AND CENTRAL OREGON

    We studied the diet of the Wild Turkey (Meleagris gallopavo) in five national forests in northern California and two national forests in central Oregon by collecting turkey droppings and analyzing them for specific food items. In all national forests the diet included insects; in all but one it included grasses. We analyzed the diet by sex and season and found that it varied seasonally and that females from California consumed more insects than did males. Seeds made up a small percentage of the diet in most national forests but constituted a majority of the diet in the Tahoe National Forest in California.

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    ABIGAIL C. MYERS, CHRISTOPHER B. GOGUEN, DANIEL C. RABBERS (Author)

    SEASONAL VARIATION IN THE DIET OF THE BARN OWL IN NORTHWESTERN NEVADA

    The Barn Owl (Tyto alba) is a widespread predator of small mammals that is declining in many parts of its range. We analyzed the Barn Owl’s diet at Stillwater National Wildlife Refuge, Churchill County, Nevada, by identifying remains in pellets collected during the summer (May–September 2007) and winter (October 2007–February 2008). In 306 pellets (143 from summer, 163 from winter), we identified 796 vertebrate prey items including 9 genera of mammals and several species of birds. At both seasons, mammals, primarily of the genera Microtus (voles), Peromyscus (white-footed mice), Reithrodontomys (harvest mice), and Dipodomys (kangaroo rats) were found in >93% of pellets. Bird remains were found in 15.5% and 11.1% of pellets in summer and winter, respectively. Remains of giant water bugs (family Belostomatidae) were present in 7.7% of summer pellets but absent in winter. Although the diet was dominated by the same five categories of prey (four mammal genera and birds) at both seasons, the proportions of Microtus and Peromyscus declined during the winter, while those of Reithrodontomys and Dipodomys increased.

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    NATHAN K. BANFIELD, PATRICIA J. NEWELL (Author)

    FIRST RECORD OF A MANGROVE YELLOW WARBLER IN ARIZONA

    On 31 July 2004 at 1130 MST we captured a Mangrove Yellow Warbler (Dendroica petechia erithachorides subspecies group), the first to be recorded in Arizona and the northernmost ever. The bird was captured in a mist net along Tonto Creek (33.75415°N, 111.22273°W), which flows into the north end of Roosevelt Lake, in Gila County about 90 km northeast of Phoenix. The bird was netted in early successional riparian habitat consisting of Goodding’s Willow (Salix gooddingii) and tamarisk (Tamarix spp.) that is established along the lake’s inflows as a result of periodic fluctuations of the lake’s level. To document this significant record, we took 15 digital photographs that clearly show diagnostic features such as a chestnut face, throat, and forecrown, thin chestnut streaks on the breast, and yellow spots on the inner webs of the rectrices (Figures 1, 2). These diagnostic photos led the Arizona Bird Committee to accept this record as the first of a Mangrove Warbler in Arizona (Rosenberg et al. 2007). Although the subspecies of the Mangrove Warbler we captured could not be ascertained, the subspecies rhizophorae breeds the closest to Arizona. It is resident in coastal mangroves north to the vicinity of Bahía Kino, Sonora, Mexico (Russell and Monson 1998), about 550 km south of Roosevelt Lake.

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    DALE W. STAHLECKER, DAVID G. MIKESIC, JAMES N. WHITE, SPIN SHAFFER, JOHN P. DeLONG, MARK R. BLAKEMORE, CRAIG E. BLAKEMORE (Author)

    PREY REMAINS IN NESTS OF FOUR CORNERS GOLDEN EAGLES, 1998–2008

    The Golden Eagle (Aquila chrysaetos) is among the most studied of raptors (Watson 1997, Kochert et al. 2002). The easiest way to monitor its diet during the breeding season has been to sample remains in active nests (Collopy 1983). In western North America, Golden Eagle nests contain remains primarily of leporids (rabbits and hares) and sciurids (ground squirrels) but also of many other species (Olendorf 1976, Palmer 1988, Kochert et al. 2002). Published information for the southwestern U. S. is limited to prey collected from 41 nests in southeastern New Mexico and western Texas in the 1960s (Mollhagen et al. 1972), nine nests in central Arizona in 1985 (Eake and Grubb 1986), and time-lapse photography and prey collected at four nests over two years in the trans-Pecos region of Texas (Lockhart 1976). Mammals, mostly hares, rabbits, and sciurids, dominate these samples.

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    DAVE TROCHLELL (Author)

    BOOK REVIEW: Small Mountain Owls

    Small Mountain Owls is a small coffee-table book that details the life histories of the Northern Pygmy Owl, Flammulated Owl, Northern Saw-whet Owl, and Boreal Owl in the western United States, primarily in Rocky Mountain National Park. The book’s text is divided into four parts, with well-ordered accounts for each of the four species that address identification, anatomy, coloration, vocalizations of adults and fledglings, distribution and range, territory size, hunting habits, diet, nesting, courtship behavior, interactions between adults and nestlings, longevity, mortality, and more.

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    JOHN STERLING (Author)

    BOOK REVIEW: Breeding Bird Atlas of Santa Clara County, California

    This book joins an expanding shelf of breeding bird atlases published since. It follows the geographic format of focusing on a single county established with the publication of the standard-setting Marin County Breeding Bird Atlas (W. D. Shuford, 1993, Bushtit Books, Bolinas, CA). Although the Santa Clara book was published in 2007, it is based on field work from 1987 to 1993, although it is updated with information on additional species breeding from 1994 to 2006. What I first noticed about this book was its size—a whopping 547 pages—which at least partly explains why the book took so long to get completed after the field work was finished. So when I read the first line of the introduction stating that the purpose of the book was to “to determine the birds that breed within a geographic area,” I was surprised. It greatly surpasses this simple stated purpose and provides a rich understanding of the breeding avifauna (and more) of Santa Clara County.

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    BRAD SCHRAM (Author)

    FEATURED PHOTO - JUVENAL PLUMAGE OF THE RUFOUS-CROWNED SPARROW

    Field guides treat the juvenile plumage of the Rufous-crowned Sparrow (Aimophila ruficeps) with varying success. The treatment itself can be misleading, perhaps because of individual variation in wear and molt. Sources of information, though not illustrations of the species’ molt and juvenile plumage, include Pyle’s (1997) Identification Guide to North American Birds and the account for The Birds of North America (Collins 1999). Although the Rufous-crowned Sparrow is widely distributed in appropriate habitat of the Southwest, California, and Mexico, in the field its juvenile plumage can pose an identification challenge.