Geology topics

M. A. Colwell

Publications and source records attributed to M. A. Colwell.

4 recordsLinked to original sources

USGS2008

Space use by Forster's Terns breeding in South San Francisco Bay

Parental care behaviors often differ in dimorphic seabirds, leading to sex-specific differences in foraging behaviors. However, few studies have examined sex-specific foraging behaviors in monomorphic seabirds. Using radio-telemetry, we studied Forster's Terns (Sterna forsteri) - a monomorphic and socially monogamous seabird - breeding in the South San Francisco Bay, California. Space use did not differ between males and females. Instead, space use varied by breeding stage and colony affiliation. Forster's Terns were located farthest from the nest during pre-breeding and post-breeding time periods, and closest to the nest during incubation and chick-rearing. Home-range size and core-use areas decreased as the breeding season progressed and were most concentrated in the post-breeding stage. The results of this and other studies indicate that tems, unlike other monomorphic seabirds studied, do not exhibit sex-specific differences in space use.

Waterbirds↗

USGS2008

Breeding stage influences space use of female American avocets in San Francisco Bay, California

Female American Avocets (Recurvirostra americana) were radio-marked (N=15) and tracked in the South San Francisco Bay, California, to determine if space use varied by breeding stage. Visual observations were used to determine breeding stage (pre-incubation, incubation, brood-rearing, post-breeding) of marked avocets. Space use measurements (linear movements, home ranges, core areas, and average distance from nest) varied significantly among breeding stages. Space use was greatest for the post-breeding stage, followed by pre-incubation, incubation, and brood-rearing. Most avocet nests (93%) were located within their pre-incubation core area boundaries, whereas only 36% of nests were within post-breeding core areas. Distance between daily location and future nest sites decreased significantly as the number of days prior to incubation decreased, suggesting that avocets prospected future nest sites several weeks prior to nesting. These data indicate that breeding stage influences space use of female American Avocets and illustrates the importance of delineating breeding stages to better understand space use of avian species.

Waterbirds↗

USGS2003

Population identification of western hemisphere shorebirds throughout the annual cycle

Identification of relationships among geographically distinct populations of migratory species can provide an understanding of breeding and natal philopatry, migration pathways, and population mixing during winter. We used random amplified polymorphic DNA (RAPD) analyses to search for markers specific to difficult‐to‐differentiate shorebird species (e.g. long‐billed dowitcher Limnodromus scolopaceus and short‐billed dowitcher L. griseus ) as well as geographically distinct breeding populations of Hudsonian godwits Limosa haemastica , red‐necked phalaropes Phalaropus lobatus , semipalmated plovers Charadrius semipalmatus , dunlin Calidris alpina , pectoral sandpipers C. melanotos , semipalmated sandpipers C. pusilla and western sandpipers C. mauri . Markers clearly differentiated all shorebird species. Estimates of population differentiation varied greatly among species ( F ST = 0.095–0.685) and correlated with interspecific variation in philopatry and geographical separation of breeding populations. We assigned individuals to putative breeding locales with greater certainty in well‐differentiated species than in poorly differentiated species. Our findings indicate specific phylogeographical structure varies among species, which has strong implications for conservation of habitats within migratory corridors. We suggest that RAPDs are useful in identifying geographical populations of migratory species and that molecular markers should be considered for tracking migratory birds throughout the annual cycle.

Molecular Ecology↗

USGS1998

Waterbird communities in rice fields subjected to different post-harvest treatments

In California's Sacramento Valley, the potential value of rice fields as habitat for waterbirds may vary with harvest method, post-harvest treatment of rice straw (chopped, burned, plowed), and extent of flooding. Recent changes in rice harvesting methods (i.e., use of stripper-headers) and a legislative mandate to decrease burning of rice straw after harvest may alter habitat availability and use. Thus, we investigated species richness and community composition of nonbreeding waterbirds during October-March 1993-94 and 1994-95 in rice fields of the northern Sacramento Valley. Most (85-91% of land area) rice was conventionally harvested (i.e., cutter bar), and the remainder was stripped. Rice straw was left untreated in more than half of fields (52% in 1994 and 54% in 1995), especially in stripped fields (56-70%). In fields where farmers treated straw, the most common management methods were plowing (15-21%), burning (19-24%), and chopping (3-5%). Fields became increasingly wet from October through March as seasonal precipitation accumulated and farmers flooded fields to facilitate straw decomposition and provide habitat for ducks. Species richness of waterbirds was greater (P < 0.002) in conventionally-harvested fields than in stripped fields; within harvest methods, species richness was consistently greater (P < 0.01) in flooded than non-flooded fields. By contrast, species richness did not differ among straw treatments (P > 0.23). Species richness in stripped fields probably was low because foraging opportunities were limited by tall dense straw, decreased grain density, and infrequent flooding. We recommend that land managers wishing to provide habitat for a diverse waterbird community harvest rice using conventional methods and flood fields shallowly.

Waterbirds↗