Audubon, California, United States
Audubon, California, United States

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Collection and analysis of demographic data play a critical role in monitoring and management of endangered taxa. I analyzed long-term clutch size and fledgling productivity data for California least tern (Sternula antillarum browni), a federally endangered subspecies that has recently become a candidate for down-listing. While the breeding population grew from approximately 1,253 to 7,241 pairs (578%) during the study period (1988-2009) both clutch size and fledgling productivity declined. Clutch size decreased by approximately 0.27 eggs (14%) from 1990-2004 then showed a moderate increase of 0.11 eggs from 2004-2009. Estimates of fledgling productivity showed a similar pattern of decline and moderate increase even after controlling for clutch size. Sea surface temperature anomalies, an index of El Niño-Southern Oscillation activity, did not influence clutch size but were associated with fledgling productivity through a non-linear relationship. Both clutch size and fledgling productivity increased with latitude, potentially indicating a gradient of life-history trade-offs. Random site effects explained little of the overall variation in clutch size (3%) or fledgling productivity (<1%) suggesting that site characteristics beyond those associated with latitude had little bearing on either measure of reproduction. Despite intensive monitoring and management, causes of variation in key demographic parameters remain poorly understood. Long-term declines in clutch size and fledgling productivity may reflect: 1) reduced food availability, 2) increased density-dependent competition, and/or 3) age-dependent reproduction coupled with a shifting population age-structure. Until the mechanisms shaping demographic parameters and population change are better understood, the success of past management and the probability of ongoing recovery will remain difficult to characterize. © 2011 Justin Schuetz.


White M.D.,Tejon Ranch Conservancy | Pandolrno E.R.,5530 Delrose Court | Jones A.,Audubon California
Western Birds | Year: 2011

The Purple Martin (Progne subis), a species of significant conservation concern in California, once nested widely in oak, sycamore, and coniferous woodlands throughout the state. Currently, the Tehachapi Mountains of southern California are the only area where significant numbers of Purple Martins are known to still nest in oaks. We surveyed for the Purple Martin and other cavity-nesting birds on a portion of Tejon Ranch in the Tehachapi Mountains during summer 2010. We found 23 nesting pairs of Purple Martins, all using cavities in large Valley Oaks (Quercus lobata) at or near the tops of ridges in open savanna settings. The Acorn Woodpecker (Melanerpes formicivorus) was the most abundant other cavity nester in the area and likely creates the cavities used by Purple Martins. The European Starling (Sturnus vulgaris), considered a serious competitor of the Purple Martin for nest sites in most of the Purple Martin's range, was rarely encountered near these nest sites.


Iglecia M.N.,Audubon California | Collazo J.A.,U.S. Geological Survey | McKerrow A.J.,U.S. Geological Survey
Avian Conservation and Ecology | Year: 2012

Expert knowledge-based species-habitat relationships are used extensively to guide conservation planning, particularly when data are scarce. Purported relationships describe the initial state of knowledge, but are rarely tested. We assessed support in the data for suitability rankings of vegetation types based on expert knowledge for three terrestrial avian species in the South Atlantic Coastal Plain of the United States. Experts used published studies, natural history, survey data, and field experience to rank vegetation types as optimal, suitable, and marginal. We used single-season occupancy models, coupled with land cover and Breeding Bird Survey data, to examine the hypothesis that patterns of occupancy conformed to species-habitat suitability rankings purported by experts. Purported habitat suitability was validated for two of three species. As predicted for the Eastern Wood-Pewee (Contopus virens) and Brown-headed Nuthatch (Sitta pusilla), occupancy was strongly influenced by vegetation types classified as "optimal habitat" by the species suitability rankings for nuthatches and wood-pewees. Contrary to predictions, Red-headed Woodpecker (Melanerpes erythrocephalus) models that included vegetation types as covariates received similar support by the data as models without vegetation types. For all three species, occupancy was also related to sampling latitude. Our results suggest that covariates representing other habitat requirements might be necessary to model occurrence of generalist species like the woodpecker. The modeling approach described herein provides a means to test expert knowledge-based species-habitat relationships, and hence, help guide conservation planning. © 2012 by the author(s).


Weinstein A.,Audubon California | Levalley R.,Mad River Biologists | Doster R.H.,U.S. Fish and Wildlife Service | Distler T.,Audubon California | Krieger K.,Audubon California
Marine Ornithology | Year: 2014

Black Oystercatcher Haematopus bachmani is considered vulnerable to decline owing to small global population size, low reproductive success and complete dependence on rocky intertidal shorelines that are impacted by human use and rising sea levels. In response to poor baseline knowledge of the population of the species in California, during 2011 we undertook the first targeted survey measuring distribution and abundance. For the mainland, we used a standardized protocol developed specifically for detecting Black Oystercatchers during the early breeding season, when pair fidelity to breeding territories is highest and movement is lowest. For the Channel Islands, government biologists used a standardized seabird monitoring protocol adapted to detect Black Oystercatchers. For the Farallones, data are taken from the literature. On the mainland, 164 observers participated in the survey in 12 of the state's 15 coastal counties. Observers surveyed approximately 9% of the mainland California coast, equalling approximately 18% of the state's mainland suitable habitat, defined below. A total of 1 160 Black Oystercatchers were detected in this subset of habitat, more than the previous estimate for the entire state (<1 000 individuals). Average density of individuals in mainland surveyed areas was 3.14 birds/km; 135 nests were positively identified, and average nest density was 0.4 nests/km surveyed. On the Northern Channel Islands, approximately 20% the total coastline (66 km), and 20% of the suitable habitat (58 km) of San Miguel, Santa Rosa, Santa Cruz, Anacapa and Santa Barbara islands was surveyed. A total of 176 adult or sub-adult Black Oystercatchers were detected. Average density of individuals in surveyed areas was 2.7 individuals/km, comparable to mainland densities. In areas thoroughly surveyed, observers found densities of nesting territories comparable with those in Alaska and British Columbia, considered the core of the species' range. Based on observed densities in surveyed areas, and including estimates from the literature and more recent observations of a population of 60 at the Farallones, we conservatively estimate a total mainland and Farallones population between 3 971 and 5 213 and a Northern Channel Islands population between 779 and 854, for a total statewide population between 4 749 and 6 067. Our results indicate that California is a critical rather than peripheral part of the Black Oystercatcher range. This result, plus ongoing threats, emphasizes the need to monitor Black Oystercatcher population trends and to identify and protect the most important habitats for Black Oystercatchers in California. The Black Oystercatcher appears highly amenable to citizen science monitoring, particularly at smaller spatial scales, owing to its life history characteristics and charismatic appeal to the public.


PubMed | Audubon California
Type: Journal Article | Journal: PloS one | Year: 2011

Collection and analysis of demographic data play a critical role in monitoring and management of endangered taxa. I analyzed long-term clutch size and fledgling productivity data for California least tern (Sternula antillarum browni), a federally endangered subspecies that has recently become a candidate for down-listing. While the breeding population grew from approximately 1,253 to 7,241 pairs (578%) during the study period (1988-2009) both clutch size and fledgling productivity declined. Clutch size decreased by approximately 0.27 eggs (14%) from 1990-2004 then showed a moderate increase of 0.11 eggs from 2004-2009. Estimates of fledgling productivity showed a similar pattern of decline and moderate increase even after controlling for clutch size. Sea surface temperature anomalies, an index of El Nio-Southern Oscillation activity, did not influence clutch size but were associated with fledgling productivity through a non-linear relationship. Both clutch size and fledgling productivity increased with latitude, potentially indicating a gradient of life-history trade-offs. Random site effects explained little of the overall variation in clutch size (3%) or fledgling productivity (<1%) suggesting that site characteristics beyond those associated with latitude had little bearing on either measure of reproduction. Despite intensive monitoring and management, causes of variation in key demographic parameters remain poorly understood. Long-term declines in clutch size and fledgling productivity may reflect: 1) reduced food availability, 2) increased density-dependent competition, and/or 3) age-dependent reproduction coupled with a shifting population age-structure. Until the mechanisms shaping demographic parameters and population change are better understood, the success of past management and the probability of ongoing recovery will remain difficult to characterize.

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