Volume 24, No. 3

DON ROBERSON (Author)

FOURTEENTH REPORT OF THE CALIFORNIA BIRD RECORDS COMMITTEE

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Western Field Ornithologists and the California Bird Records Committee (CBRC) are again pleased to thank Bushnell, a division of Bausch & Lomb, for its continued generous support in helping to sponsor the publication of these reports.

This report details 412 records from the California Bird Records Committee’s review of older records, of which 276 (67%) were accepted. Both the number of records and the number of contributing observers (268) represent new highs for a Committee report. Our tenth report (Dunn 1988) described our attempt over the past decade to review not only all current reports of rarities in California, but available documentation on all published records of species on our Review List, no matter how long ago the bird occurred. We not only actively solicited written details and photographs from observers, we scoured the literature for additional information and attempted to locate and photograph for Committee files all extant specimens of vagrants to California. These data are now permanently archived. Reported here is our review of 42 specimens, some dating as far back as 1862, and our consideration of other documentation generated from 1935 to 1989.

STEVE N. G. HOWELL, STEVEN J. ENGEL (Author)

SEABIRD OBSERVATIONS OFF WESTERN MEXICO

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Southern Mexico’s offshore Pacific avifauna has been rather little studied. Murphy (1958) and Jehl (1974) reported observations from cruises that passed through Mexican waters in November and December 1956 and in April 1973, respectively. Pitman (1986) mapped the relative abundance of 57 species of seabirds in the eastern tropical Pacific on the basis of 4333 hours of observation between 1974 and 1984; only a small number of these 4333 hours (81 noon positions, 55 of which were off Baja California), however, pertain to Mexican waters (i.e., within 200 nautical miles of Mexican territory), and 74% of the 81 noon positions were between October and March (R. L. Pitman pers. comm.). Pitman’s atlas provides an excellent large-scale picture but lacks data on seasonal status of species, and the scale employed does not enable one to interpret local distributions. Other records of seabirds off western Mexico are widely scattered and mostly derive from nearshore land-based trips of a day or less (e.g., Binford 1970, 1989).

The Middle American Trench runs from the vicinity of the Islas Tres Marias, Mexico, to the Cocos Ridge, south of Costa Rica. The trench lies some 55–110 km (mean distance 75 km) offshore between Jalisco and Guerrero and is 15–50 km (mostly 20–30 km) wide. The trench is at least 3600 m deep, mostly 4300–4650 m deep from central Jalisco south, and increases to 5000–5200 m deep off central Guerrero; submarine mountains in the trench off Colima (Manzanillo) and Guerrero (Zihuatanejo) reduce depths to 3600 m. On either side of the trench waters quickly shallow to 2700–3200 m, and inshore the 1000-fathom (1800-m) contour line lies 20–55 km (mostly 35–55 km) off the coast.

From 28 April to 6 May 1992 we observed seabirds off western Mexico out to 100 km from shore, that is, from just offshore of to well inshore of the Middle American Trench, between the vicinity of Cabo Corrientes, Jalisco, and Acapulco, Guerrero. Here we describe the birds observed during our visit.

SAM FITTON (Author)

SCREECH-OWL DISTRIBUTION IN WYOMING

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The discovery that the Eastern (Otus asio) and Western (O. kennicottii) Screech-Owls are incipient (Marshall 1967) if not full species (AOU 1983) motivated field ornithologists along the presumed Rocky Mountain contact zone to learn how to distinguish the two and to determine their distributions. Progress toward this determination has been slow in Wyoming because there are few field ornithologists available to do the necessary studies. With this in mind, I sought to find evidence for these species from previous work and surveyed appropriate habitat to contribute original information.

DAN L. REINKING, STEVE N. G. HOWELL (Author)

AN ARCTIC LOON IN CALIFORNIA

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At 1415 on 2 November 1991 we found an Arctic Loon (Gavia arctica sensu stricto) at Abbott’s Lagoon, Point Reyes National Seashore, in Marin County, California. We observed the bird for about an hour at ranges down to about 250 m with binoculars and spotting scopes. It was a clear day, and we had the sun at our backs. After completing field notes and sketches, we returned home to consult the literature and notify other birders. We returned the following morning and, with several other birders, soon located the loon and observed it for over 2 hours. Additional notes were taken as the bird swam intermittently to within 100 m and then farther out into the fog. The following description and Figures 2 and 3 are derived from our notes and sketches taken from 1415 to 1515 on 2 November and from 0845 to 1100 on 3 November. The bird was last reliably reported on 17 November. Other observers photographed and videotaped (Figure 1) the bird, and the identification has been accepted by the California Bird Records Committee.

OWEN A. KNORR (Author)

NOTES: BREEDING OF THE BLACK SWIFT IN THE GREAT BASIN

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The Black Swift (Cypseloides niger) has an extensive albeit somewhat disjunct range in western North America from southern Canada south to southern California (Foerster and Collins 1990) and Arizona (Knorr 1989) and east to Colorado (Knorr 1950, 1961). Its range in the Great Basin has been unclear. I found several breeding colonies on the eastern margin in Provo Canyon, Utah (Knorr 1962), but until 1986 my subsequent attempts to locate Black Swift colonies elsewhere in the Great Basin were unsuccessful. Even so, observations by Ridgway (1874) suggested that there might be other sites located along the western margin of the Great Basin.

RICHARD J. CAMP, RICHARD L. KNIGHT, JERRY FREILICH (Author)

NOTES: COMMON RAVEN POPULATIONS IN JOSHUA TREE NATIONAL MONUMENT, CALIFORNIA

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Common Raven (Corvus corax) numbers in the Mojave Desert have grown substantially, with increases ranging from 5 to 15% annually over the past 20 years (Robbins et al. 1986, USDI 1990). These population increases, and the location of Desert Tortoise (Gopherus agassizii) shells near raven nests and perches, have resulted in ravens being suggested as a cause of the decline of tortoise populations (Berry 1985, Berry et al. 1986).

The conclusion that raven populations have increased is based on Breeding Bird Surveys, in which birds are counted from roadsides (Robbins et al. 1986). Estimates of raven populations are thus based on data from areas of diverse human land uses including agriculture, livestock grazing, and urban/suburban development. Knight and Kawashima (in press), however, found that raven numbers can be considerably greater along highways than away from them. Currently, there is no information on raven numbers in areas away from roads and not grazed by livestock.

Accordingly, we surveyed raven numbers in native desert scrub away from roads. Our goal was to determine a baseline estimate of raven population density in a part of the Mojave Desert suitable for nesting ravens but free from contemporary land-use changes.

JENNIFER K. FREY (Author)

NOTES: NOCTURNAL FORAGING BY SCISSOR-TAILED FLYCATCHERS UNDER ARTIFICIAL LIGHT

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I observed nocturnal foraging by Scissor-tailed Flycatchers (Tyrannus forficatus) on 27 April 1992 at College Station, Brazos County, Texas. Sunset was at 2001 central daylight time. At approximately 2130 I saw an adult Scissor-tailed Flycatcher perched on a utility wire below a street light adjacent to a busy four-lane highway. A second Scissor-tailed Flycatcher arrived at approximately 2200. It perched on the utility wire about 1 m from the first bird. Both flycatchers hunted flying insects attracted to, or illuminated by, the street light. The flycatchers were not observed to chase insects beyond the lighted area. After pursuing an insect the birds returned immediately to their perch. Insect species that the birds were preying on were not identified but included several moths. The two birds continued foraging until at least 2300 when I discontinued my observations.