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Bird Age (bird + age)
Selected AbstractsMigratory connectivity in a declining bird species: using feather isotopes to inform demographic modellingDIVERSITY AND DISTRIBUTIONS, Issue 4 2010Thomas S. Reichlin Abstract Aim, Conservation programmes for endangered migratory species or populations require locating and evaluating breeding, stopover and wintering areas. We used multiple stable isotopes in two endangered European populations of wrynecks, Jynx torquilla L., to locate wintering regions and assess the degree of migratory connectivity between breeding and wintering populations. Location, Switzerland and Germany. Methods, We analysed stable nitrogen (,15N), carbon (,13C) and hydrogen (,D) isotopes from wing feathers from two populations of wrynecks to infer their wintering origins and to assess the strength of migratory connectivity. We tested whether variation in feather isotopic values within the Swiss population was affected by bird age and collection year and then considered differences in isotopic values between the two breeding populations. We used isotopic values of summer- and winter-grown feathers to estimate seasonal distributions. Finally, we calculated a species-specific ,D discrimination factor between feathers and mean annual ,D values to assign winter-grown feathers to origin. Results, Bird age and collection year caused substantial isotopic variation in winter-grown feathers, which may be because of annually variable weather conditions, movements of birds among wintering sites and/or reflect asynchronous moulting or selection pressure. The large isotopic variance in winter-grown feathers nevertheless suggested low migratory connectivity for each breeding population, with partially overlapping wintering regions for the two populations. Main conclusions, Isotopic variance in winter-grown feathers of two breeding populations of wrynecks and their geographical assignment point to defined, albeit overlapping, wintering areas, suggesting both leapfrog migration and low migratory connectivity. On this basis, integrative demographic models can be built looking at seasonal survival patterns with links to local environmental conditions on both breeding and wintering grounds, which may elucidate causes of declines in migratory bird species. [source] Surface wear of incoloy and darvic bands on Atlantic Puffin adults and chicksJOURNAL OF FIELD ORNITHOLOGY, Issue 2 2006André R. Breton ABSTRACT Bands are a common marking method in bird studies and capture-mark-reencounter (CMR) models are often used to analyze banding data. Common to this family of models are two assumptions: marks do not fall off or become unreadable and individuals within groups remain equally detectable. When data fail to meet these assumptions, results of CMR analyses may be biased. In studies of long-lived seabirds exposed to coarse nesting substrates, band wear is especially problematic. We compared surface wear from abrasion against rocks on incoloy and darvic bands applied to a long-lived seabird, the Atlantic Puffin (Fratercula arctica). In 2003 and 2004, surface wear on bands applied to chicks and adults was scored at five colonies in the Gulf of Maine. We used logistic regression to analyze two subsets of these data by fitting the probability of being worn (one or more characters difficult to read or obliterated) to band age, bird age, and band type. In both analyses, an evidence ratio provided exclusive support for the model that included all factors. Immature puffins largely avoid colonies and remain at sea until their second or third summer after hatching. Consequently, probabilities of being worn were delayed on both band types by 4 yr on bands applied to chicks compared to adults. Based on our estimates, 25% and 87% of darvic bands applied to chicks and adults, respectively, were worn after 5 yr. Wear was reduced by 71% and 87% annually on incoloy compared to darvic bands applied to adults and chicks, respectively. To uphold assumptions of CMR models, we recommend incoloy bands over darvic in studies spanning more than about 5 yr of long-lived seabirds exposed to coarse substrates. SINOPSIS Las anillas colocadas en las patas son un método común de marcar aves y se han establecido modelos (recuento de aves marcadas , siglas en inglés CMR) para analizar los datos obtenidos de esta forma. Hay dos postulados que deben aceptarse en estos modelos: que las anillas no se pierden o que se puedan leer y que los individuos marcados y no-marcados tienen la misma probabilidad de ser contados. Cuando los datos no cumplen con las dos condiciones previamente mencionadas el análisis de CMR puede contener sesgo. En estudios de ave marinas que viven por mucho tiempo, el desgaste de las anillas crea problemas. Comparamos el desgaste y daño de anillas de metal (niquel-cromio y acero) y anillas de plástico (policloruro de vinilo) colocadas en individuos de Fratercula arctica. Durante el 2003 y 2004, estudiamos el desgaste y daño de anillas colocadas a pichones y adultos del ave en cinco colonias de estas en el Golfo de Maine. Utilizamos una regresión logística para analizar dos conjuntos de datos sobre la probabilidad de desgaste (uno o más caracteres en la anilla difíciles de leer) a la edad de la anilla (tiempo en la pata del ave), edad del ave y tipo de anilla. Las aves inmaduras, evitan los grupos en las colonias y permanecen en el mar hasta el segundo o tercer verano. Como resultado, la probabilidad de que ambos tipos de anillas hubieran estado desgastadas o dañadas en los juveniles se dilato por unos cuatro años, al ser este grupo comparado con los adultos. El 25% y el 87% de las anillas plásticas colocadas en pichones y adultos, respectivamente, estaban desgastadas a los cinco años. El desgaste en las anillas de metal se redujo en un 71% y 87% anual al compararse con las plásticas colocadas en adultos y pichones, respectivamente. Para cumplir con los postulados de los modelos CMR, recomendamos el uso de anillas de metal en aquellos estudios pautados para más de cinco años particularmente en aves marinas que utilizan o se exponen a sustratos duros. [source] Individual dispersal among colonies of Little Egrets Egretta garzettaIBIS, Issue 2 2002Mauro Fasola Colonial waterbirds are unusual in that competition for nest-sites or mates may occur at a scale of a few metres, whereas thousands of birds may overlap in their foraging range at a larger scale. Dispersal has been evaluated for only a few such species, and its adaptive significance remains unclear. We studied Little Egret dispersal among all the colonies within the Camargue, southern France. The overall probability of dispersal between successive years was 0.45. The probability of dispersal was unaffected by a bird's age, or by any density-dependent effect of colony size. Juveniles dispersed at distances that would be expected if colony selection were random, while adults tended to remain within 10 km of their previous colony. We found no obvious environmental ,trigger' for an individual to disperse. Although our evidence is inconclusive, the short dispersal distances of adults are not consistent with foraging conditions as the primary trigger for dispersal. Little Egrets generally forage within 8 km of their colony, so birds dispersing less than 10 km would gain little advantage in response to unfavourable foraging conditions. Our data, with 75% of dispersing birds coming from decreasing colonies and 72% joining increasing colonies, suggest that individual dispersal depended on colony dynamics as a whole, i.e. (1) a social component of dispersal at the individual level, or (2) a simultaneous colony response to unfavourable environmental conditions or (3) both. Further investigation at a higher social level may be necessary to understand dispersal of this colonial nesting species. [source] |