Western Birds Journal

Volume 34, No. 4

Published October 1, 2003

Issue description

Volume 34, number 4 of Western Birds, published 2003

Articles

  1. Cover image V34 (4)

    THOMAS P. RYAN, CHARLES T. COLLINS (Author)

    ACTIVITY PATTERNS OF WHITE-THROATED SWIFTS IN CALIFORNIA

    We investigated the daily and seasonal activity patterns of the White-throated Swift and related these patterns to seasonal changes in day length and variation in environmental conditions. The time of morning exit from the roost fluctuated more with daily variation in the weather than by season, occurring later after sunrise when temperatures were cool, particularly during winter. Exit time was also delayed if temperatures rapidly exceeded the optimal range for aerial insect activity shortly after sunrise. Exits were further delayed by rain. The evening return of White-throated Swifts to their roost fluctuated more predictably with season, although entry times were also influenced by weather. Entry time was delayed when temperatures were cold and occurred earlier when they were warm or hot, or during rain. The pattern of group entry varied by season. In winter, evening roost entry was clumped, with large numbers of swifts entering together. In spring, entry was more scattered, with smaller groups entering over a longer period. The pattern of morning exit was clumped year-round, with most swifts exiting together as a group.

  2. Cover image V34 (4)

    THOMAS P. RYAN, CHARLES T. COLLINS (Author)

    SEASONAL POPULATION FLUCTUATION OF WHITE-THROATED SWIFTS AT ROOST SITES IN SOUTHERN CALIFORNIA

    In southern California, White-throated Swift (Aeronautes saxatalis) roosts contain many more individuals during the winter months than during the breeding season. Dates of the high and low counts at these roosts fluctuate from site to site and from year to year. Evidence suggests that some individuals remain and nest at or near the roost; whether others migrate north to breeding areas remains unknown.

  3. Cover image V34 (4)

    THOMAS P. RYAN, CHARLES T. COLLINS (Author)

    SOCIAL BEHAVIOR OF WHITE-THROATED SWIFTS

    The social behavior of the White-throated Swift includes Chases Without Contact, Chases With Contact, and Courtship Falls. These behaviors show a strong seasonal pattern. Chases Without Contact were the most common interaction and occurred most frequently during the winter and spring. Chases With Contact and Courtship Falls occurred less frequently and peaked during spring prior to breeding. White-throated Swifts also exhibit social behaviors that may be termed the Raised-Wing display, Screaming Party, and Silent Dread.

  4. Cover image V34 (4)

    ALLISON D. RUDALEVIGE, DESSlE L. A. UNDERWOOD, CHARLES T. COLLIN (Author)

    DIET OF BREEDING WHITE-THROATED AND BLACK SWIFTS IN SOUTHERN CALIFORNIA

    We analyzed the diet of nestling White-throated (Aeronautes saxatalis) and Black Swifts (Cypseloides niger) in southern California. White-throated Swifts fed their nestlings boluses of insects that were more taxonomically diverse, on average (over 50 arthropod families represented), than those fed by Black Swifts (seven arthropod families, primarily ants). In some cases, White-throated Swift boluses contained primarily one species, while other boluses showed more variation. In contrast, all Black Swift samples contained high numbers of winged ants with few individuals of other taxa. Our results provide new information on the White-throated Swift’s diet and support previous studies of the Black Swift.

  5. Cover image V34 (4)

    MANUEL MARIN (Author)

    MOLT, PLUMAGE, BODY MASS, AND MORPHOMETRICS OF A POPULATION OF THE WHITE-THROATED SWIFT IN SOUTHERN CALIFORNIA

    Over a 10-year period, I examined molt patterns, plumage, and body-mass changes in a population of White-throated Swifts in the Mecca Hills, Riverside County, California, by sampling birds at regular roosts each month from February through November. The swifts used the roosts year-round, but numbers declined in March, then increased in June and July after breeding. As a result of plumage wear, the juvenal plumage can be categorized into three “phases”: prior to fledging, after fledging, and prior to the first prebasic molt. I found no sexual dimorphism in wingspan, wing length, tarsus length, tail length, culmen length, or body mass. I found an average difference between the sexes in the depth of the tail fork, but because of much overlap, it cannot be used to determine the sex of individuals. The maximum difference between highest and lowest body mass was 28.7%, less than reported for other species. Testis size began to increase in March, reaching a peak in April. Primary molt lasted 6–7 months, from May through November. Tail molt lasted about 2.5–3 months, from June through August. Breeding began at this desert site one to two months earlier than at a coastal site. The overlap of breeding and molt in this desert population appears to be less than reported for other species of swifts.

  6. Cover image V34 (4)

    JOHN E. HUNTER (Author)

    CHARACTERISTICS OF TREES USED BY NESTING AND ROOSTING VAUX'S SWIFTS IN NORTHWESTERN CALIFORNIA

    Given the limited information available on trees used by Vaux’s Swifts (Chaetura vauxi) in the coast redwood (Sequoia sempervirens) zone of California, we gathered information regarding site, tree, and nest characteristics of nest and roost trees found opportunistically by various observers. All 14 nest trees and four roost trees were redwoods. Twelve of the nests were found in basal hollows in large live trees (mean diameter at breast height [dbh] 306 cm); one was in a cavity formed at the base of two small live trees (dbh about 50 cm) that had grown together, and one was in a stump (height 1.3 m, dbh 128 cm). Three of the four roost trees were dead with broken tops; their mean height and dbh were 20.0 m and 229 cm, respectively. The fourth was a live tree 33.9 m in height and 297 cm in dbh. These trees were in areas experiencing varying levels of human activity. All nests were located well away from cavity entrances. Our findings suggest that fire plays an important role in the creation of suitable nest and roost trees and that the swifts’ tradition of using specific suitable trees lasts for many years.

  7. Cover image V34 (4)

    EVELYN L. BULL (Author)

    DECLINES IN THE BREEDING POPULATION OF VAUX'S SWIFTS IN NORTHEASTERN OREGON

    I investigated trends in the breeding population of Vaux’s Swift (Chaetura vauxi) in northeastern Oregon by revisiting in 2003 39 stands of trees that contained swifts in 1991. In 2003, the number of swifts in these stands was significantly fewer, with only 46% of the stands still containing swifts. Only 29% of the 58 nest and roost trees the swifts were using from 1989 to 1997 were still suitable for nesting in 2003; the remainder had fallen over, broken off, or become filled with cavities. Factors that may be affecting the population include tree mortality caused by insect outbreaks and disease, tree harvesting, wildfire, climatic shifts, and habitat changes in the winter range.

  8. Cover image V34 (4)

    DANIEL A. AIROLA, JESSE GRANTHAM (Author)

    PURPLE MARTIN POPULATION STATUS, NESTING HABITAT CHARACTERISTICS, AND MANAGEMENT IN SACRAMENTO, CALIFORNIA

    The Purple Martin (Progne subis) has been eliminated from most of California’s Central Valley. The last known population nests in elevated roadways (“bridges”) in the city of Sacramento. We reviewed bird records (1949–1990), conducted surveys to assess population size and trend (1991–2002), and evaluated management actions to protect and increase populations. Martins ceased nesting in buildings in Sacramento in the 1960s and 1970s as the European Starling (Sturnus vulgaris) population expanded, but adoption of vertical weep holes for nesting beneath bridges in the 1960s has allowed martins to persist. The known Sacramento population increased from four to seven colonies and from approximately 105 to 135 nesting pairs from 1992 to 2002. Martin colonies are located in longer (>85 m) bridge sections that provide at least 6 m of unobstructed airspace beneath the colonies. Management has included a pilot project to insert wire “nest guards” in weep holes to increase survival of young and protection of nesting colonies during construction activities near nests. Initial results indicate that nest guards reduce mortality of young falling from nests and do not result in increased competition for nest sites by starlings and other species. Exclusion of martins from nesting at a large colony to prevent disturbance from a construction project reduced nesting use of the site; such exclusion is not considered necessary to protect nesting birds. Martin recovery may require substantial management, including protecting and enhancing existing colonies, encouraging colonization of other elevated road sites, establishing martin use of artificial nest structures in unoccupied regions, and enlisting public adoption of management responsibility.

  9. Cover image V34 (4)

    David Lukas (Author)

    BOOK REVIEWS: Raptors of Western North America,

    Even in the brave new world of in-depth family monographs, Brian Wheeler's two volumes tread where few have wandered before. North America has long lacked a guide comparable to Dick Forsman's brilliant The Raptors of Europe and the Middle East, and Wheeler is the first to attempt to remedy this situation. The result is monumental, staggering in its scope, and, quite frankly, a mixed bag. If nothing else, these books break new ground in the world of raptor identification: there are a lot of ideas that go beyond what has been suggested before, many of which need to be tested in the field—some that may become standard in the future, others that will fall by the wayside. In two books with such detail, there is a tremendous amount of material to review. And while there are many errors, omissions, or nit-picky details to quibble over, it must be said that this is a highly commendable, deeply personal, and intensely scholarly effort on Wheeler's part. All North American birders and raptor specialists have much to learn from these books.

  10. Cover image V34 (4)

    Steve N. G. Howell (Author)

    BOOK REVIEWS: Pipits and Wagtails

    This addition to the growing series of identification guides to bird families treats only the 18 species of pipits and 9 of wagtails recognized by the authors as occurring in the Holarctic biogeographic region (ostensibly Eurasia and North America). The title is thus misleading, in that the book does not treat about half of the world's species of the Motacillidae. This approach, however, has advantages over the more common one of including all of the world's species in a given family, despite an author's lack of familiarity with many species. And the authors of Pipits and Wagtails have spent many years studying this group of birds, rather than deciding one day that they would simply like to write a book. As a consequence, Pipits and Wagtails stands virtually alone in this recent series: it is authoritative, well written, and full of literature citations. It should be a model for any future works in this genre.

  11. Cover image V34 (4)

    MARSHALL J. ILIFF (Author)

    FEATURED PHOTO: A VAGRANT BELL'S SPARROW IN BAJA CALIFORNIA SUR

    Although at least seven Sage Sparrow subspecies have been described, the species has generally been regarded as comprising five distinct subspecies (AOU 1957). Nominate belli is resident in chaparral from the inner northern Coast Ranges of California south to the coast in Marin County, and south along the coast and foothills through northern Baja California, west of the Sierra Juárez and Sierra San Pedro Mártir, to Santa Catarina Landing at 29°30′ N. Isolated populations occur in the western Sierra Nevada from El Dorado County south to Mariposa County (Grinnell and Miller 1944).