California gull

Abstract: : We examined patterns of depredation of duck nests by 9 species and 2 congeneric species-groups of predators in the Prairie Pothole Region: coyote (Canis latrans), red fox (Vulpes vulpes), raccoon (Procyon lotor), striped skunk (Mephitis mephitis), American badger (Taxidea torus), mink (Mustela vison), weasels (ermine M. erminea) and long-tailed weasel (M. frenata), Franklin's ground squirrel (Spermophilus franklin ii), black-billed magpie (Pica pica), American crow (Corvus brachyrhynchos), and gulls (ring-billed gull LARUS DELAWARENSIS and California gull L. californicus). We discuss factors affecting amount and types of evidence of depredation left by predators at duck nests, including characteristics of eggs and nest sites, behavior of ducks and predators, anatomy and size of predators, and effects of other animals. Accounts of depredation patterns of individual predator species and species-groups are provided and include summaries of positive and negative indicators of depredation. Information presented is mostly from studies we conducted during 1972-92, which involved offering duck eggs to captive and free-ranging predators and monitoring responses by direct observation, time-lapse camera, or revisiting sites. Variables of depredation were quantified on nest depredation records and included disturbances of eggs, ground surface, and nest material. Patterns of depredation of some predator species varied little (e.g., red fox) but patterns of others varied greatly (e.g., coyote). There was much overlap of patterns among some predator species (e.g., Franklin's ground squirrel, weasels). A format with instructions for preparing nest depredation records is provided. Recommendations for interpreting depredation records are discussed. We applied recommendations to 389 depredation records from waterfowl production areas in Minnesota, North Dakota, and South Dakota and discuss outcomes of that exercise.

Abstract: We recovered passive integrated transponder (PIT) tags from nine piscivorous waterbird colonies in the Columbia River basin to evaluate avian predation on Endangered Species Act (ESA)-listed salmonid Oncorhynchus spp. populations during 2007–2010. Avian predation rates were calculated based on the percentage of PIT-tagged juvenile salmonids that were detected as passing hydroelectric dams and subsequently were consumed and deposited by birds on their nesting colonies. Caspian terns Hydroprogne caspia (hereafter, “terns”) and double-crested cormorants Phalacrocorax auritus (hereafter, “cormorants”) nesting on East Sand Island in the Columbia River estuary consumed the highest proportions of available PIT-tagged salmonids, with minimum predation rates ranging from 2.5% for Willamette River spring Chinook salmon O. tshawytscha to 16.0% for Snake River steelhead O. mykiss. Estimated predation rates by terns, cormorants, gulls of two species (California gull Larus californicus and ring-billed gull L. ...

Abstract: Pugesek (1981) recently claimed to demonstrate an increase in reproductive effort with age in the California gull Larus californicus. On the contrary, neither theory nor his own data support Pugesek's claim. Older parents invest no more time in (1) foraging for the young and (2) guarding the nest than do younger parents, but the former are (a) more effective at providing food for the young and (b) more efficient at alternating and coordinating guarding and feeding duties. The increase in territorial defense with age is likely due to older parents having more mature young to defend. Development of parental skills as a result of experience best explains the observed increase in reproductive success with age.

Abstract: We analyzed data on numbers and annual trends of breeding terns and gulls based on censuses of all colonies of the Caspian Tern (Sterna caspia), Forster’s Tern (S. forsteri) and California Gull (Larus californicus) in the San Francisco Bay estuary from 1982 to 2003. All species used nesting substrates that were flat, largely non-vegetated, had a wide view in all directions, and were composed of sand, gravel, or earth. The estuary supported 17, 13, and seven colonies of each species, respectively. Nesting terns were primarily on salt evaporation pond islands and tidal islands. The largest colony of California Gulls was on a deactivated salt pond. Total numbers of each species in 2003 were about 2,300, 2,450 and 21,200 breeding birds, respectively. Numbers of Forster’s Terns declined significantly during the study, while California Gulls increased, and the number of Caspian Terns was stable. Numbers of each species at each colony site have shown considerable annual variation. We attribute the lack ...