Common Terns nesting at Bermuda are isolated by 1,000–4,000 km from other populations of the species around the North Atlantic Ocean. This population experienced a severe demographic bottleneck as a ...result of a hurricane in 2003 and was subsequently re-established by four males and four females. Using seven microsatellite loci, we compared the genetic diversity of the pre- and post-bottleneck populations, compared the genetic profile of the Bermuda population with those of other populations around the North Atlantic Ocean and mainland Europe, and assessed the potential contribution of immigration to genetic diversity. We found a loss of genetic diversity (number of alleles and heterozygosity) in the post-bottleneck Bermudian population (4.6–2.9 and 0.56–0.52, respectively). We also report significant differentiation among all sampled locations (global F
ST
= 0.16) with no evidence for immigration into Bermuda. Common Terns from the Azores were genetically more similar to those from mainland North America than to those from Bermuda or mainland Europe. Our results suggest that the critically endangered population in Bermuda is genetically distinct and requires continued and enhanced conservation priority.
We used 22 yr of capture–mark–reencounter (CMR) data collected from 1988 to 2009 on about 12,500 birds at what went from three to five coastal colony sites in Massachusetts, New York, and ...Connecticut, United States, to examine spatial and temporal variation in breeding dispersal/fidelity rates of adult Roseate Terns (Sterna dougallii). At the start of our study, Roseate Terns nested at only one site (Bird Island) in Buzzards Bay, Massachusetts, but two more sites in this bay (Ram and Penikese Islands) were subsequently recolonized and became incorporated into our CMR metapopulation study. We examined four major hypotheses about factors we thought might influence colony‐site fidelity and movement rates in the restructured system. We found some evidence that colony‐site fidelity remained higher at long‐established sites compared with newer ones and that breeding dispersal was more likely to occur among nearby sites than distant ones. Sustained predation at Falkner Island, Connecticut, did not result in a sustained drop in fidelity rates of breeders. Patterns of breeding dispersal differed substantially at the two restored sites. The fidelity of Roseate Terns at Bird dropped quickly after nearby Ram was recolonized in 1994, and fidelity rates for Ram soon approached those for Bird. After an oil spill in Buzzards Bay in April 2003, hazing (deliberate disturbance) of the terns at Ram prior to the start of egg‐laying resulted in lowering of fidelity at this site, a decrease in immigration from Bird, and recolonization of Penikese by Roseate Terns. Annual fidelity rates at Penikese increased somewhat several years after the initial recolonization, but they remained much lower there than at all the other sites throughout the study period. The sustained high annual rates of emigration from Penikese resulted in the eventual failure of the restoration effort there, and in 2013, no Roseate Terns nested at this site.
Ten geolocators (light-level data loggers) were attached to Common Terns (Sterna hirundo) at a breeding site in the northeastern USA in 2007 and 2008; six were retrieved (five with useful data) in ...2008 and 2009. The birds wintered in four discrete areas on the north and east coasts of South America, from Guyana (6–7°N) to northeastern Argentina (36–42°S); three remained within restricted areas for most or all of the winter, whereas two ranged more widely. They left the breeding area at various dates between 1 August and 14 September; three migrated directly from the breeding area while two first moved southwest to stage near Cape Hatteras. All five birds flew directly to the vicinity of Puerto Rico, then moved along the north and east coasts of South America, staging at scattered locations for periods of 3–11 d, before reaching their winter quarters at various dates from 6 September to 26 October. Two birds left their winter quarters on 2 March and 4 April, staged in northern Brazil for 47 and 6 d, then traveled via the Bahamas to reach the breeding site on 1 May. During breeding and post-breeding periods, the birds spent a mean of 7 min each day and virtually no time at night resting on the water, but during the rest of the year they often rested on the water for up to 6 h by day and up to 11 h at night. Leg-mounted geolocators caused several adverse effects but did not reduce survival.
Use of soft-metal (aluminum alloy) bands on gulls (Laridae) is known to result in high rates of band loss and, as a result, hard-metal (monel, incoloy, or stainless steel) bands are superior for most ...studies. However, the U.S. Bird Banding Laboratory (BBL) and the Canadian Wildlife Service Bird Banding Office continue to issue soft bands for use on gulls, and the BBL does not make specific recommendations about use of hard bands so many banders continue to use soft bands. For wholly marine species of gulls banded in North America since 1996, ~20% have been banded with soft bands; the proportion of soft bands used on partially freshwater gulls was ~70% up to 2009, but has since fallen to 40%. Using hierarchical Bayesian models in program MARK, we analyzed recovery data for three gull species and found that estimates of annual survival rates derived from soft bands (0.68–0.81) were lower than those derived from hard bands (0.85–0.96). Comparison of survival rates of Herring Gulls (Larus argentatus) in the Great Lakes basin and on the Atlantic coast provided no evidence that soft bands last longer in freshwater than saltwater. Band loss compromises many types of studies, including those assessing the possible effects of climate change. We recommend that use of soft bands on gulls be discontinued, and that banders be required to use hard bands on these species in the future. The same consideration applies to other long-lived species, including some waterfowl and all albatrosses, pelicans, cormorants, shearwaters, petrels, terns, shorebirds, and alcids. Use of hard bands should be based on expectations about a species' longevity and evidence of band wear, rather than on whether or not it occurs in saltwater. Es reconocido que el uso de anillos de metal blando (aleaciones de aluminio) en gaviotas (Laridae) resulta en tasas elevadas de perdida de los anillos. En consecuencia, anillos de metal duro (monel, incoloy o acero inoxidable) son de superior calidad para la mayoría de los estudios. Sin embargo, el Laboratorio de Anillamiento de Aves de Estados Unidos (U.S. Bird Banding Laboratory, BBL) y la Oficina de Anillamiento de Aves del Servicio Canadiense de Fauna Silvestre (Canadian Wildlife Service Bird Banding Office) continúan produciendo anillos de metal suave para su uso en gaviotas, y particularmente el BBL no hace recomendaciones especificas sobre el uso de anillos de metal duro. Por esta razón muchos anilladores continúan usando anillos blandos. Del total de individuos de gaviotas totalmente marinas de Norte América anillados desde 1996, ~20% ha sido anillado usando anillos blandos; la proporción de anillos blandos usados en gaviotas de agua dulce era del ~70% hasta el 2009 pero ha disminuido desde entonces al 40%. Usando modelos Bayesianos jerárquicos en el programa MARK, analizamos datos de recapturas de tres especies de gaviotas y encontramos que las tasas anuales de supervivencia son menores cuando son estimadas a partir de datos de anillos blandos (0.68–0.81) que cuando son estimadas a partir de datos de anillos duros (0.85–0.96). Las comparaciones de las tasas de supervivencia en Larus argentatus entre la cuenca de los Grandes Lagos y en la costa Atlántica no sugieren que los anillos blandos tengan una duración mayor en agua dulce que en agua salada. Recomendamos que se descontinúe el uso de anillos blandos en gaviotas y que los anilladores utilicen anillos duros para estas especies en el futuro. La misma consideración aplica para otras especies longevas, incluyendo algunas aves acuáticas y todos los albatroses, pelicanos, cormoranes, pardelas, petreles, gaviotines, aves playeras y álicidos. Las decisión sobre el uso de anillos duros debe ser basada en la longevidad de las especies y la evidencia del desgaste del anillo más bien que en la pregunta si la especie ocurre o no en agua salada.
Abstract In response to stressors, most vertebrates elevate secretion of glucocorticoids (CORT) to produce a ‘stress response’ that enhances survival, but simultaneously inhibits reproduction. ...Circumstances in which the value of current reproduction is high relative to the value of future reproduction and survival, often lead to suppression of the stress response thus ensuring that critical resources are not diverted away from reproduction. Consistent with this expectation, we have previously reported that the magnitude of the stress response (maximum levels of CORT) declines with age in breeding adults of a long-lived seabird, the common tern ( Sterna hirundo ). While age-related changes in the stress response may be common in vertebrates, the mechanisms that underlie them are poorly understood. The glucocorticoid stress response is regulated by the hypothalamic–pituitary–adrenal (HPA) axis, and one mechanism that may contribute to an age-related decline in the stress response is changes in adrenal capacity (adrenal sensitivity to ACTH and/or an ability to secrete CORT in response to ACTH). To test this hypothesis, we captured and injected 92 known-aged adult common terns ( Sterna hirundo ) ranging in age from 3 to 29 years with either a control saline or an experimental adrenocorticotropin (ACTH) solution and measured the effects on stress-induced CORT after 30 min of restraint. In both treatment groups, stress-induced CORT significantly declined with age, suggesting that a decrease in adrenal capacity contributes to a reduction in the stress response in older adults.
Little is known about sublethal effects on birds of low level exposure to oil. White blood cell parameters (total leukocyte counts and/or differentials) were measured in blood samples from Common ...Terns (Sternahirundo; n = 71) exposed to low levels of oil from an oil spill in Buzzards Bay, Massachusetts, in 2003. Data from Common Terns (n = 16) sampled at the same site in a non-spill year were used for reference. Total leukocytes and lymphocytes were severely depressed when individuals were first sampled, 14–20 days after the spill, and returned to near to or above reference levels by day 39. Heterophils and heterophil/lymphocyte ratios were markedly elevated 14–20 days after the spill, and returned to below reference levels by day 39. These changes were closely parallel to changes in hematocrit in the same birds, but hematocrits were not correlated with white blood cell parameters, suggesting that mechanisms of action were different. The combination of immune suppression and anemia during the physiologically demanding period prior to and during egg-laying is likely to have caused adverse effects on reproduction.
Hematocrits were measured in Common Terns (Sterna hirundo) (n = 75) that were exposed to oil from a spill in Buzzards Bay, Massachusetts, USA, in 2003, and that laid eggs 17–39 days following the ...spill. Comparative data were obtained in three pre- and two post-spill years and from three unoiled reference sites. In non-spill years, annual means of hematocrit varied in parallel with breeding performance. Hematocrits were lower (mean 45.3, n = 75) and more variable in the oil spill year than in non-spill years, and 20% of birds sampled were anemic (hematocrit < 41.7). However, hematocrits were almost as low (mean 46.4, n = 44) in 2002, a year with naturally adverse conditions. In 2002, hematocrits and body-masses were depressed following two storms and recovered in parallel following the storms; hematocrits were positively correlated with body-mass and ambient temperature and negatively correlated with wind speed. In contrast, in 2003 hematocrits were negatively correlated with body-mass and temperature and positively correlated with wind speed. Hematocrits were very low (mean 39.8, n = 15) when birds were first sampled 20–23 days after the spill and recovered toward normal levels by day 39 (mean 49.4, n = 14). Reduced hematocrits can be a useful indicator of sublethal oil intoxication, especially in females, provided that they are not associated with low body-masses or adverse weather. Measuring hematocrits could be useful for rapid screening of populations sublethally exposed to oil.
Reproductive success declines over the course of the breeding season in many bird species. Two categories of hypothesis have been evoked to explain this decline. The "timing" hypothesis suggests that ...seasonal declines in breeding success are attributable to the date of laying. The "parental quality" hypothesis suggests that seasonal declines result from the fact that young, inexperienced, or low quality birds breed later in the season. To evaluate the relative importance of timing and parental quality, egg exchanges and removals were used to manipulate hatching dates of common terns Sterna hirundo. Indices of quality, attendance, provisioning rates, and reproductive success of birds in three experimental groups (delayed hatch pairs, advanced hatch pairs, and pairs induced to relay) were compared to those of date-matched controls. Pairs that hatched chicks early raised more chicks than pairs hatching chicks late in the season, regardless of initial laying date. This suggests that hatching chicks early is advantageous in itself. Our results, however, also support the parental quality hypothesis. There was a significant negative relationship between natural laying date and fledging success, independent of hatching date. Differences in chick growth and survival suggest that higher quality adults may be able to compensate for the disadvantages of late hatching dates and achieve similar reproductive success to that of pairs hatching chicks early. We found that pairs hatching chicks late in the season were subject to more incidents of kleptoparasitism than those hatching chicks early. This may be a proximate factor contributing to seasonal declines in reproductive success for common terns, although such a mechanism would not be likely in non-colonial species. Failure to control for egg quality may have biased the results of some prior egg exchange experiments. Additionally, altered cost of incubation may be an unavoidable confounding factor in studies designed to manipulate timing of breeding.
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