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At least 307 records · Page 17Linked to original sources
USGS1996

Allocation of limited reserves to a clutch: A model explaining the lack of a relationship between clutch size and egg size

Lack (1967, 1968) proposed that clutch size in waterfowl is limited by the nutrients available to females when producing eggs. He suggested that if nutrients available for clutch formation are limited, then species producing small eggs would, on average, lay more eggs than species with large eggs. Rohwer (1988) argues that this model should also apply within species. Thus, the nutrition-limitation hypothesis predicts a tradeoff among females between clutch size and egg size (Rohwer 1988). Field studies of single species consistently have failed to detect a negative relationship between clutch size and egg size (Rohwer 1988, Lessells et al. 1992, Rohwer and Eisenhauer 1989, Flint and Sedinger 1992, Flint and Grand 1996). The absence of such a relationship within species has been regarded as evidence against the hypothesis that nutrient availability limits clutch size (Rohwer 1988, 1991, 1992; Rohwer and Eisenhauer 1989).

The Auk↗
USGS1996

Reproductive success, growth and survival of black-crowned night-heron ( Nycticorax nycticorax ) and snowy egret ( Egretta thula ) chicks in coastal Virginia

We studied reproductive success, growth, and survival of Black-crowned Night-Heron ( Nycticorax nycticorax ) and Snowy Egret ( Egretta thula ) chicks in two mixed-species heronries on marsh islands in Chincoteague Bay, Accomack County, Virginia in 1992 and 1993. We attached radio transmitters with mortality sensors to the oldest chicks (A-chicks) in 11 to 22 nests of both species to monitor survival during the mid- to late nestling period and into the postnesting dispersal period. For both species, we found significant differences between 1992 and 1993 in growth rates and survival. Mass growth rates of chicks were higher in 1993 than in 1992 for both species. Culmen-length growth rates varied significantly due to year-colony effects for night-herons, but only for hatching order for egrets. Differences in survival rates due to hatching order were found for the egrets in both years, but were found only in 1992 for night-herons. As with mass growth rates, survival of chicks was higher in 1993 than 1992. Survival of radio-marked A-chicks did not differ between species or years for the period from hatching to fledging or from fledging through the end of the study (ca. two months postfledging). Survival ranged from 0.80 to 1.00 from the time radio transmitters were attached (ca. two weeks of age) until dispersal age (53-55 days for egrets; 55-60 days for night-herons). After birds left the colony, survival rates were lower during the next 40 to 55 days, ranging from 0.25 to 0.60. These results suggest that, at least for Snowy Egrets, A-chicks may be buffered from annual variations in food conditions, but that growth and survival of other brood members may provide a barometer of local conditions. Despite problems of variability in measurement, some of these parameters show promise as bioindicators of estuarine conditions. We recommend that a cost-efficient wading-bird monitoring program would include: (1) estimating numbers of nesting birds of selected species (e.g. Snowy Egrets) at particular estuaries, and (2) monitoring "initial brood sizes" and survival of young to at least two weeks of age in a sample of nests for each focal species. However, additional biomonitoring (e.g. marsh forage fish, contaminant loads) is necessary to evaluate how well top trophic-level organisms such as fish-eating birds respond to changes in estuarine production or quality.

The Auk↗
USGS1996

In memoriam: Robert Earl Stewart, Sr., 1913-1993

Robert Earl Stewart, Sr., our colleague, close friend, and mentor, was born on 16 April 1913 in Kansas City, Missouri. He graduated from high school in Grimes, Iowa, received his B.S. in Biology from the University of Iowa in 1936, and his M.S. in Zoology from the University of Michigan in 1937. His post-graduate work on the life history of the Common Yellow throat was published in the Wilson Bulletin in 1953. Bob joined the AOU in 1938, was made an Elective Member in 1949, and a Fellow in 1974. During World War II, he served with the U.S. Navy Medical Corps in the Pacific Theater.

The Auk↗
USGS1997

Changes in breeding bird populations in North Dakota: 1967 to 1992-93

We compared breeding bird populations in North Dakota using surveys conducted in 1967 and 1992-93. In decreasing order, the five most frequently occurring species were Horned Lark ( Eremophila alpestris ), Brown-headed Cowbird ( Molothrus ater ), Western Meadowlark ( Sturnella neglecta ), Red-winged Blackbird ( Agelaius phoeniceus ), and Eastern Kingbird ( Tyrannus tyrannus ). The five most abundant species - Horned Lark, Chestnut-collared Longspur ( Calcarius ornatus ), Red-winged Blackbird, Western Meadowlark, and Brown-headed Cowbird - accounted for 31-41% of the estimated statewide breeding bird population in the three years. Although species composition remained relatively similar among years, between-year patterns in abundance and frequency varied considerably among species. Data from this survey and the North American Breeding Bird Survey indicated that species exhibiting significant declines were primarily grassland- and wetland-breeding birds, whereas species exhibiting significant increases primarily were those associated with human structures and woody vegetation. Population declines and increases for species with similar habitat associations paralleled breeding habitat changes, providing evidence that factors on the breeding grounds are having a detectable effect on breeding birds in the northern Great Plains.

The Auk↗
USGS1997

Sources of variation in waterfowl survival rates

Because of the need to manage hunted populations of waterfowl (Anatidae), biologists have studied many demographic traits of waterfowl by analyzing band recoveries. These analyses have produced the most extensive and best estimates of survival available for any group of birds. Using these data, we examined several factors that might explain variation among annual survival rates to explore large-scale patterns that might be useful in understanding waterfowl population dynamics. We found that geography, body mass, and tribe (i.e. phylogeny) were important in explaining variation in average waterfowl survival rates.

The Auk↗
USGS1998

Guts don't fly: Small digestive organs in obese Bar-tailed Godwits

We documented fat loads and abdominal organ sizes of Bar-tailed Godwits (Limosa lapponica baueri ) that died after colliding against a radar dome on the Alaska Peninsula, most likely just after takeoff on a trans-Pacific flight of 11,000 km, and of birds of the same subspecies just before northward departure from New Zealand. We compared these data with data on body composition of godwits of the smaller lapponica subspecies obtained during a northward stopover in The Netherlands. As a consequence of high amounts of subcutaneous and intraperitoneal fat, and very small fat-free mass, Bar-tailed Godwits from Alaska had relative fat loads that are among the highest ever recorded in birds (ca. 55% of fresh body mass). Compared with northbound godwits from New Zealand, the Alaskan birds had very small gizzards, livers, kidneys, and guts. This suggests that upon departure, long-distance migrants dispense with parts of their "metabolic machinery" that are not directly necessary during flight, and rebuild these organs upon arrival at the migratory destination.

The Auk↗
USGS1998

Reproductive success of Belding's Savannah Sparrows in a highly fragmented landscape

Habitat fragmentation can influence the abundance and distribution of birds. Decreases in patch size increase the amount of edge habitat, which can allow greater invasion by exotic species, predators, and brood parasites (Hagan and Johnston 1992, Donovan et al., 1995). Fragmented habitats may act as population sinks and result in local extinctions unless immigration occurs from source habitats (Pulliam 1988, Howeet al., 1991, Pulliam et al., 1992, Stacey and Taper 1992). Fragmentation is especially severe in coastal California, where about 75% of the presettlement acreage of coastal wetlands has been lost to development (Zedler 1982, Zedler and Powell 1993). This degradation has produced a highly fragmented landscape that may have a negative influence on the Belding's Savannah Sparrow ( Passerculus sandwichensis beldingi ), which is one of two wetland-dependent bird species endemic to coastal salt marshes in southern California. This nonmigratory subspecies is listed as endangered by the State of California. Statewide censuses of Belding's Savannah Sparrows reveal wide fluctuations in local population sizes, with local extinctions occurring in some years (Zembalet al. 1988). Thus, the population dynamics of Belding's Savannah Sparrow may reflect the effects of fragmentation.

The Auk↗
USGS1997

Declines in abundance and species richness of birds following a major flood on the upper Mississippi River

We examined the abundance and species richness of birds breeding in floodplain forests of the Upper Mississippi River from 1992 to 1994 to identify effects of a major flood in 1993 on the bird assemblage. Sixty-five study plots were divided into treatments and controls based on whether they were flooded in 1993. Among 84 species observed on all plots, 41 species decreased in abundance from 1992 to 1994, 13 species increased, and numbers of 5 species were unchanged. Sample sizes were inadequate to evaluate trends for 25 species. Species richness declined over the three-year period. The main effect "year" was significant in 20 of the 36 species tested. Cool, wet conditions may have contributed to poor reproductive success in 1993 and resulted in widespread declines in abundance during the year following the flood. Bird abundance increased on most unflooded plots in 1993, probably because birds were displaced from flooded plots. This pattern was most striking for Neotropical migrants, species preferring habitat edges, lower-canopy nesters, and species that forage in the air. We suggest that periodic major flooding maintains suitable floodplain habitat for Prothonotary Warblers ( Protonotaria citrea ) in the face of competition with House Wrens ( Troglodytes aedon ) for nest sites.

The Auk↗
USGS1997

Capture-recapture analysis of a wintering black-capped chickadee population in Connecticut, 1958-1993

We investigated the dynamics of a wintering population of Black-capped Chickadees ( Parus atricapillus ) using data from a long-term capture-recapture study. Goodness-of-fit and likelihood-ratio tests indicated that the standard Jolly-Seber model was inadequate for the data, so we explored different parameterizations of a model in which survival probability for new captures differed from that of previously marked birds. One possible explanation for the lower local survival rate of new captures is that some of the birds were transients that had no chance of being recaptured. Average survival probability over the entire period was 0.62, and the estimated fraction of transients among unmarked birds was 0.27. We found evidence that chickadee survival rates were lower in years immediately following establishment of the Tufted Titmouse ( Parus bicolor ) as a territorial species (after 1967) than during years immediately preceding this event. We found no evidence that chickadee survival rates were lower in the years immediately following establishment of territorial raptors (after 1984) than during preceding years. Evidence suggested a long-term decline in survival probability from 1959 to 1991.

The Auk↗
USGS1997

Migration by radio-tagged pacific golden-plovers from hawaii to Alaska, and their subsequent survival

Many Pacific Golden-Plovers ( Pluvialis fulva ) and other shorebirds winter in the Hawaiian Islands. This is the first landfall for mid-Pacific migrants after overwater flights of 4,000 km or more from Alaska (Johnson et al. 1989, Johnson and Connors 1996). Previous findings (sightings of marked birds and wing-length measurements) showed Alaska affinities for golden-plovers wintering in Hawaii (Johnson and Connors 1996), but there had been no attempt to demonstrate movements between the two regions using radiotelemetry. We made such an effort in spring 1996 by radio-tagging plovers on wintering grounds in Hawaii just before their migration. Some of these birds were later found at three sites in Alaska, including a breeding ground,

The Auk↗
USGS1997

Forty-first supplement to the American Ornithologists' Union Check-list of North American birds

This seventh supplement after the publication of the 6 th edition (1983) of the AOU Check-list of North American Birds includes taxonomic and nomenclatural changes adopted by the Committee on Classification and Nomenclature between 15 March 1995 and 15 March 1997. Because this will be the last supplement before the publication of the 7 th edition of the Check-list , it also summarizes other decisions made by the Committee since 1983 that were not intended to affect the 6 th edition but rather were to lay the foundation for its successor. Most of those decisions relate to sequence or rank of certain taxonomic categories. The Committee believes that compendia such as the Check-list are not appropriate places for the first appearance of novel taxonomic treatments or rearrangements. Therefore, we take the opportunity of this supplement to inform you of the ways in which the 7 th edition will differ from the 6 th . The style of this supplement differs from that of the previous six because they were designed to provide detailed changes to the text in the 6 th edition; this one also is to provide information on how the 7 th edition will differ from the 6 th . Many details on reasons for the change will be discussed in the Preface or text of the new volume.

The Auk↗
USGS1997

Significance of stomach oil for reproduction in seabirds: An interspecies cross-fostering experiment

Stomach oil, a complex mixture of neutral dietary lipids, is a unique attribute of seabirds in the order Procellariiformes. With the exception of diving-petrels, all procellariiforms produce stomach oil and feed it to their young. We conducted an interspecies cross-fostering experiment on Bird Island, South Georgia, that was designed to reveal how the presence or absence of stomach oil in meals fed to young seabirds influences their growth, development, and survival. Hatchling South Georgia Diving-Petrels ( Pelecanoides georgicus ), a species that lacks stomach oil, were switched with hatchling Antarctic Prions ( Pachyptila desolata ), a species that feeds its young stomach oil. Diving-petrel foster parents did not successfully raise prion nestlings, presumably due to the absence of stomach oil in meals fed to nestlings. Prion foster parents successfully raised diving-petrel nestlings to fledging, but growth rates were lower, nestling fat reserves were lower, and fledging was delayed compared with controls. These results suggest that stomach oil is an essential dietary component for prion nestlings to meet their energy requirements, but diving-petrel nestlings apparently cannot efficiently assimilate stomach oil. This experiment supports the hypothesis that the production of stomach oil is an adaptation that allows breeding seabirds to enhance provisioning rates of energy to the nest, while foraging on a distant and dispersed food supply.

Georgia↗
USGS1997

In memoriam: John Warren Aldrich, 1906-1995

John Aldrich was born in Providence, Rhode Island, on 23 February 1906, and went to the Providence public schools. He developed a broad interest in natural history at an early age, being stimulated by his mother, a kindergarten teacher, who introduced him to nature books. His interest was strengthened by Harold L. Madison, Director of the Park Museum in Providence, an Associate ( = member) of the AOU. As a high school student, John taught nature study at the Rhode Island Boy Scout Camp in summers. John was President of his class at Classical High School, and manager of the school's football team in his senior year. Also in that year, 1923, John published his first paper, a note in Bird-Lore on the occurrence of the Mockingbird in Rhode Island. That paper is a literary gem, showing that his skill in writing developed as early as his knowledge of birds. His early interest in football continued as well; he was a devoted fan of the Washington Redskins in his later years.

The Auk↗
USGS1999

Harlequin Duck recovery from the Exxon Valdez oil spill: A population genetics perspective

Concerns about Harlequin Duck ( Histrionicus histrionicus ) population recovery following the Exxon Valdez oil spill led biologists to ask whether birds located in different molting and wintering areas belong to genetically distinct and, thus, demographically independent populations. Owing to the lack of direct observations of movements among marine areas, three classes of genetic markers that differed in mode of inheritance were used to evaluate the degree of genetic differentiation among wintering areas within Prince William Sound (PWS) and the Alaska Peninsula and Kodiak Archipelago (APKA). We could not reject the null hypothesis that the wintering aggregations within each region are composed of a single genetically panmictic population. Differences in genotype frequencies among wintering locations within PWS and APKA were low and nonsignificant for all three classes of markers. Furthermore, we saw no evidence for deviations in Hardy-Weinberg equilibrium or gametic disequilibrium between loci within a winter collection site as would be expected if these locales were composed of individuals from reproductively isolated (and genetically distinct) breeding locales. Finally, no evidence for significant structuring was noted between PWS and APKA. Lack of spatial genetic structuring could be due to the cumulative effects of low levels of gene flow over long time periods, low levels of gene flow by immature birds moving between marine habitats, or to episodic dispersal caused by habitat alteration (e.g. volcanic eruptions). Harlequin Ducks are likely to recolonize or enhance populations in areas recovering from environmental damage via emigration of birds from non-affected areas. Demographic studies suggest, however, that levels of movements are low, and that population recovery by emigration is a long-term process.

The Auk↗
USGS1999

Factors influencing counts in an annual survey of Snail Kites in Florida

Snail Kites ( Rostrhamus sociabilis ) in Florida were monitored between 1969 and 1994 using a quasi-systematic annual survey. We analyzed data from the annual Snail Kite survey using a generalized linear model where counts were regarded as overdispersed Poisson random variables. This approach allowed us to investigate covariates that might have obscured temporal patterns of population change or induced spurious patterns in count data by influencing detection rates. We selected a model that distinguished effects related to these covariates from other temporal effects, allowing us to identify patterns of population change in count data. Snail Kite counts were influenced by observer differences, site effects, effort, and water levels. Because there was no temporal overlap of the primary observers who collected count data, patterns of change could be estimated within time intervals covered by an observer, but not for the intervals among observers. Modeled population change was quite different from the change in counts, suggesting that analyses based on unadjusted counts do not accurately model Snail Kite population change. Results from this analysis were consistent with previous reports of an association between water levels and counts, although further work is needed to determine whether water levels affect actual population size as well as detection rates of Snail Kites. Although the effects of variation in detection rates can sometimes be mitigated by including controls for factors related to detection rates, it is often difficult to distinguish factors wholly related to detection rates from factors related to population size. For factors related to both, count survey data cannot be adequately analyzed without explicit estimation of detection rates, using procedures such as capture-recapture.

The Auk↗
USGS1999

Annual survival of Snail Kites in Florida: Radio telemetry versus capture-resighting data

We estimated annual survival of Snail Kites ( Rostrhamus sociabilis ) in Florida using the Kaplan-Meier estimator with data from 271 radio-tagged birds over a three-year period and capture-recapture (resighting) models with data from 1,319 banded birds over a six-year period. We tested the hypothesis that survival differed among three age classes using both data sources. We tested additional hypotheses about spatial and temporal variation using a combination of data from radio telemetry and single- and multistrata capture-recapture models. Results from these data sets were similar in their indications of the sources of variation in survival, but they differed in some parameter estimates. Both data sources indicated that survival was higher for adults than for juveniles, but they did not support delineation of a subadult age class. Our data also indicated that survival differed among years and regions for juveniles but not for adults. Estimates of juvenile survival using radio telemetry data were higher than estimates using capture-recapture models for two of three years (1992 and 1993). Ancillary evidence based on censored birds indicated that some mortality of radio-tagged juveniles went undetected during those years, resulting in biased estimates. Thus, we have greater confidence in our estimates of juvenile survival using capture-recapture models. Precision of estimates reflected the number of parameters estimated and was surprisingly similar between radio telemetry and single-stratum capture-recapture models, given the substantial differences in sample sizes. Not having to estimate resighting probability likely offsets, to some degree, the smaller sample sizes from our radio telemetry data. Precision of capture-recapture models was lower using multistrata models where region-specific parameters were estimated than using single-stratum models, where spatial variation in parameters was not taken into account.

The Auk↗
USGS1998

Morphological adaptation with no mitochondrial DNA differentiation in the coastal plain swamp sparrow

We estimated genetic differentiation between morphologically distinct tidal marsh populations of Swamp Sparrows ( Melospiza georgiana nigrescens ) and the more widespread inland populations ( M. g. georgiana and M. g. ericrypta ). The tidal marsh populations are consistently grayer with more extensive black markings (particularly in the crown), and their bills are larger. These differences are variously shared with other species of salt marsh birds and small mammals. We analyzed mitochondrial DNA sequences (5′ end of control region, COII/t-lys/ATPase8, and ND2) of Swamp Sparrows and found low levels of genetic variation and no evidence of geographic structure. These results suggest a rapid and recent geographic expansion of Swamp Sparrows from restricted Pleistocene populations. Morphological differentiation has occurred without long-term genetic isolation, suggesting that selection on the divergent traits is intense. The grayer and more melanistic plumage is probably cryptic coloration for foraging on tidal mud, which tends to be grayish as a result of the formation of iron sulfides, rather than iron oxides, under anaerobic conditions.

The Auk↗