Helen Hays

Estimating Annual Survival and Movement Rates of Adults within a Metapopulation of Roseate Terns

Several multistratum capture-recapture models were used to test various hypotheses about possible geographic and temporal variation in survival, movement, and recapture/resighting probabilities of 2399 adult Roseate Terns (Sterna dougallii) color-banded from 1988 to 1992 at the sites of the four largest breeding colonies of this species in the northeastern USA. Linear-logistic ultrastructural models also were developed to investigate possible correlates of geographic variation in movement probabilities. Based on goodness-of-fit tests and comparisons of Akaikes Information Criterion (AIC) values, the fully parameterized model (Model A) with time- and location-specific survival, movement, and capture probabilities, was selected as the most appropriate model for this metapopulation structure. With almost all movement accounted for, on average >90% of the surviving adults from each colony site returned to the same site the following year. Variations in movement probabilities were more closely associated with the identity of the destination colony site than with either the identity of the colony site of origin or the distance between colony sites. The average annual survival estimates (0.74-0.84) of terns from all four sites indicate a high rate of annual mortality relative to that of other species of marine birds.

HIERARCHICAL BAYES FOR STRUCTURED, VARIABLE POPULATIONS: FROM RECAPTURE DATA TO LIFE‐HISTORY PREDICTION

Understanding population dynamics requires models that admit the complexity of natural populations and the data ecologists obtain from them. Populations possess structure, which may be defined as “fixed” stages through which individuals pass, with superimposed variability among individuals and groups. Data contain missing values and inaccurate censuses. From limited data ecologists attempt to predict life history schedules and population growth. We extend the “missing value” framework for Bayesian analysis of structured populations to admit the heterogeneity in demography and the limitations of data that are typical of ecological populations. Our hierarchical treatment of capture–recapture data allows inference on demographic rates contained in matrix transition models for populations that may be stratified by location and by other variables. Simulations with artificial data sets demonstrate the ability of the Bayesian model to successfully estimate underlying parameters, even with incomplete census data. In contrast, traditional nonhierarchical models may lead to biased parameter estimates because of variation in recapture rates of individuals. Analyses of published demographic data on Common Terns and Taitu Hills rats illustrate the utility of the model. Predictive distributions of maturation age, survivorship, and population growth demonstrate profound impacts of population and data complexity.

INTROMITTENT ORGAN MORPHOLOGY AND TESTIS SIZE IN RELATION TO MATING SYSTEM IN WATERFOWL

Abstract The waterfowl family Anatidae is one of very few avian taxa that possesses an intromittent organ. This paper examines the adaptive significance of the intromittent organ in waterfowl by determining the relationships between intromittent organ morphology and the intensity of sperm competition (as reflected by frequency of forced extrapair copulations [FEPCs]). Intromittent organ morphological characteristics, including length and circumference (adjusted for body size), number of ridges and knobs (per unit area), ridge or knob height, ridge or knob span, and area covered by ridges and knobs, were measured from scaled drawings of museum specimens of 54 waterfowl species (33 genera), 27 of which were ranked by frequency of FEPC (1 = monogamous, 2 = rare FEPC, 3 = frequent FEPC, and 4 = polygynous or promiscuous). Testes sizes were also investigated in relation to FEPCs, where testes mass (adjusted for body size) from 44 species (24 genera) were obtained (29 species with mating strategies). The size of the testes, the length of the intromittent organ, the height of the intromittent organ ridges and knobs, and the area covered by ridges and knobs increased significantly with the frequency of FEPC, and those relationships exist after correcting for common ancestry constraints. These results are consistent with the hypothesis that waterfowl intromittent organs are involved in sperm competition. Further research into the actual mechanism by which the intromittent organ is involved would be worthwhile.

Sources of variation in loss rates of color bands applied to adult roseate terns (Sterna dougallii) in the western North Atlantic

ABSTRAcr.-A model-based analysis was done to test several hypotheses concerning the rates of loss of butt-ended color bands placed on adult Roseate Terns (Sterna dougallii) in the western North Atlantic. These birds were captured and color banded from 1987-1991 at four colony sites, and recaptured from 1989-1992 as part of a study of the population dynamics of this species. Two types of color bands, Darvic and celluloid, were used, but only one band type was used for each individual bird. Each bird was given three color bands. The estimated probability that a bird with all color bands present during one breeding season still had all color bands during the next breeding season was 0.87. The analysis provided no evidence that colony site, cohort, calendar year of banding, age of color band, or whether or not the bands were heat-sealed closed, were important sources of variation in band-retention prob

Temporal variation in adult survival rates of Roseate Terns during periods of increasing and declining populations

Abstract We used 19 years of mark-recapture/resighting data collected on 11,020 birds from 1988-2006 at five colony sites in Massachusetts, New York, and Connecticut, USA, to examine temporal variation in the survival rates of adult Roseate Terns (Sterna dougallii) during periods of overall population increase (1988-2000) and decline (2000-2006). Roseate Terns nested at only one colony site in Buzzards Bay, Massachusetts at the start of this period, but two more sites in this area were recolonized as the study progressed. Adult survival rates varied temporally in different ways at the different colony sites, but for the five sites combined they did not differ between the period of overall population increase (0.835 ± 0.006 SE) and the period of population decline (0.835 ± 0.008 SE). As expected based on previous work, adult survival from 1991 to 1992 was lowered as a result of a severe hurricane in August 1991. An oil spill in Buzzards Bay in April 2003 did not appear to result in lower survival of the birds nesting at the sites in this area compared to those nesting at the other two study sites in New York and Connecticut. Temporal variation in other vital rates of this species (such as postfledging survival) needs to be examined to determine the likely cause(s) of the recent population decline.

Feeding Grounds, Daily Foraging Activities, and Movements of Common Terns in Southern Brazil, Determined by Radio-telemetry

Abstract Fourteen Common Terns (Sterna hirundo) were radio-tagged on their wintering grounds at Lagoa do Peixe, Rio Grande do Sul state, southern Brazil. Aerial radio-tracking was made along 850 km from northern Rio Grande do Sul state to Montevideo, Uruguay. During 23.6 h of tracking in February 2003, we recorded 100 locations of 12 radio-tagged terns. Birds were located within a range of 165 km from the tagging area, and most locations were at sea (74 at sea vs. 26 roosting on the beach), due to frequent movement of the birds when feeding and most tracking during feeding periods. Each bird was located 4-14 times (mean = 8.3 locations/bird). Common Terns fed predominantly between 15-20 m isobaths (56% of at sea locations), and 10-15 m isobaths (32%), which corresponded to a maximum of 8 km offshore. Minimum distance traveled in five days of intensive tracking was 46 km, and maximum distance was 167 km. Daily movement was 19 km on average (minimum 6 km d-1, maximum 49 km d-1). Nine out of 12 birds were found at sea in both early morning and late afternoon periods. Eight out of 12 birds were recorded feeding at sea in consecutive periods of the day (morning and afternoon), indicating two feeding trips a day.

Banded Roseate Terns from different continents trapped in the Azores

Abstract Banded Roseate Terns (Sterna dougallii) trapped on nests in the Azores illustrate that, during the nonbreeding season, birds from the Azores are found on the coast of Africa in groups of Roseate Terns from northern Europe and on the coast of South America with birds from the northeastern U.S. and the Caribbean. One Roseate Tern, probably originally banded on a nest in a western Atlantic colony, suggests the possibility of gene flow between these colonies and the Azores.

Recovery in Punta Rasa, Argentina of Common Terns Banded in the Azores Archipelago, North Atlantic

Abstract We report the southernmost recoveries of Common Terns (Sterna hirundo) banded in the Azores archipelago, North Atlantic. Two birds banded as chicks and one bird banded as an adult were recovered at Punta Rasa, Argentina, adding support to the hypothesis of a regular movement of Common Terns between the Azores and the South American coast rather than to the African coast.

The Pink Feather Blush of the Roseate Tern

Abstract Roseate Terns (Sterna dougallii) were observed and/or netted on the coast of Bahia, Brazil in January and/or February from 1996 through 2003 as well as in November 2005. The breasts of almost all netted Roseate Terns examined were washed with pink. Analysis of breast feathers taken from birds during the breeding season indicates the pink color is carotenoid-based, with astaxanthin as a major component. Pigment concentration was low, measured in micrograms of carotenoids per gram of feather (maximum recorded 6.2 μg of carotenoids g-1 of feathers), compared to milligram quantities in overtly red feathers in other species, and varied markedly among individuals. A pink blush apparently characterizes the plumage of the Roseate Tern for most of the year, often being more prominent in January/February during the non-breeding season than in breeding birds in May.