Showing papers by "Vincent Bretagnolle published in 2000"

Responses of an avian predator to variations in prey density at a temperate latitude

Abstract: Fluctuating prey populations and their effects on avian predator population dynamics have been studied particularly at high latitudes, where prey populations, especially microtines, are known to be cyclic; raptors show both numerical and functional responses to variations in their prey. In this paper, we investigate the response of a migratory raptor (Montagu's Harrier, Circus pygargus) to variations in abundance of its main prey (common vole, Microtus arvalis) in France. We document multiannual fluctuation in the abundance of common voles. The numerical response of Montagu's Harrier to this variable food supply was studied using breeding parameters (breeding density, breeding phenology, and various measures of breeding success). Breeding density and mean clutch size were strongly correlated with spring vole abundance, whereas mean brood size at fledging was correlated positively with summer vole abundance. The mechanism involved in the numerical response of Montagu's Harrier indicates that dispersal and ...

Predation risk and moonlight avoidance in nocturnal seabirds

Abstract: Unlike most seabird families, the vast majority of small petrel species are nocturnal on their breeding grounds. Further, they reduce markedly their activity when the light level increases. Moonlight avoidance might be a consequence of reduction in foraging profitability, as bioluminescent prey do not come to the sea surface on bright nights. Alternatively, petrels may avoid colonies during moonlit nights because of increased predation risk. We studied predation on petrels by Brown Skuas Catharacta antarctica lonnbergi at Kerguelen, and the influence of moonlight on behaviour of both skuas and petrels, to test the ‘predation risk’ hypothesis. On the study area, Brown Skuas hunt at night and prey heavily upon the Blue Petrel Halobaena caerulea and the Thin-billed Prion Pachyptila belcheri. Predation risk was higher on moonlit nights, as skuas caught more prey, and particularly more Blue Petrels when the light level increased. Nightly intakes of Blue Petrel and Thin-billed Prion by skuas was related to colony attendance of non-breeders rather than that of breeders. Biometry of prey also suggested that skuas caught a higher proportion of non-breeding birds than was present at the colonies. Predation risk was thus greater in non-breeders and on moonlit nights. Colony attendance by non-breeding Blue Petrels and Thin-billed Prions was also reduced during moonlit nights. Vocal activity, which is mainly by non-breeders, was also drastically reduced when the light level increased in the species suffering the highest predation rate. Our results supported the ‘predation risk’ hypothesis, although the ‘foraging efficiency’ and the ‘predation risk’ hypotheses are not mutually exclusive: the former might explain the moonlight avoidance behaviour of breeding, and the latter that of non-breeding individuals.

Black Rats, Island Characteristics, and Colonial Nesting Birds in the Mediterranean: Consequences of an Ancient Introduction

Abstract: The devastation of island faunas by alien species has been instrumental in raising concerns about the global threat to biological diversity. Colonial nesting species, often restricted to islands, have been affected severely. Eradication of introduced species as a means to alleviate the problem is usually done with little or no understanding of the mechanisms governing interactions between introduced and native species. Such an understanding could help target management action. We analyzed how island area, rock substrate, bird spe- cies biology, and presence of an introduced species, the black rat ( Rattus rattus ), interact to explain the distri- bution and abundance of colonial nesting birds on a set of 72 islands from six archipelagos in the western Mediterranean. Rats were introduced to this region over 2000 years ago, and these communities have had time to reach an equilibrium. Using general linear models, we show that rats have affected species distribu- tions more on the smaller islands and on islands with an acidic or neutral rock substrate; larger bird species are more resistant. On the smaller islands, where rat densities are highest, larger colonial birds are negatively affected. On larger islands, where rat densities are lower and fluctuate form year to year, larger colonial birds can maintain healthy populations despite the presence of rats. Although rats caused local extinction or reduc- tion in bird abundance, the presence of islands varying in size and/or substrate allowed most archipelagos to retain their suite of colonial nesting bird species, despite a presumably reduced abundance for most species. Resumen: La devastacion de las faunas islenas por especies forasteras ha sido instrumental en lo que re- specta a elevar preocupaciones sobre la amenaza global contra la diversidad biologica. Las especies de ni- dacion colonial, frecuentemente restringidas a islas, han sido severamente afectadas. La erradicacion de es- pecies introducidas como un medio para aliviar el problema es generalmente realizada con poco o ningun entendimiento de los mecanismos que gobiernan las interacciones entre las especies nativas y las introduci- das. Este tipo de entendimiento podria ayudar a enfocar medidas de manejo. Nosotros analizamos como el area, el substrato rocoso, la biologia de la especie de ave, y la presencia de una especie introducida, la rata negra ( Rattus rattus ), interactuan para explicar la distribucion y abundancia de aves con nidacion colonial en 72 islas de seis archipielagos en el Mediterraneo occidental. Las ratas fueron introducidas a esta region hace mas de 2000 anos y estas comunidades han tenido tiempo suficiente para alcanzar un equilibrio. Medi- ante el uso de modelos lineales generales mostramos que las ratas han afectado mas la distribucion de espe- cies en las islas pequenas y en las islas grandes con un substrato rocoso acido o neutro (textura burda), que en aquellas islas con caliza y textura fina. Las especies de aves mas pequenas son mas sensibles a las ratas, mas frecuentemente ausentes de las islas con ratas y sistematicamente ausentes de islas con ratas y un sub- strato rocoso de estructura burda. Las especies de aves mas grandes son mas resistentes. En las islas mas pe-

Genetic relationships of cory's shearwater: parentage, mating assortment, and geographic differentiation revealed by dna fingerprinting

Abstract: We used DNA fingerprinting to assess genetic structure of populations in Cory's Shearwater (Calonectris diomedea). We analyzed mates and parent-offspring relationships, as well as the amount and distribution of genetic variation within and among populations, from the level of subcolony to subspecies. We found no evidence of extrapair fertilization, confirming that the genetic breeding system matches the social system that has been observed in the species. Mates were closely related, and the level of genetic relatedness within populations was within the range usually found in inbred populations. In contrast to previous studies based on allozymes and mtDNA polymorphism, DNA fingerprinting using microsatellites revealed consistent levels of genetic differentiation among populations. However, analyzing the two subspecies separately revealed that the pattern of genetic variation among populations did not support the model of isolation by distance. Natal dispersal, as well as historic and/or demographi...

Sex and age determination of short- eared owl nestlings

Abstract: We studied plumage patterns of known-sex nestling and juvenile Short-eared Owls (Asio flammeus) to develop a sexing technique for nestlings in the field. Markings on the secondaries varied according to sex, and differences were apparent from about 10–15 days of age. We also provide aging formulas based on mass for nestlings up to 15 days of age and on wing length for nestlings older than that age. Finally, we evaluate growth parameters according to sex. The asymptotes of body mass, wing length, and tarsus length growth curves were higher in females than males. The inflexion point was attained earlier by males than by females.

Model on a population and prediction on another one: a generalized discriminant rule

Abstract: Traditionally, discriminant analysis in a decision purpose proceeds in the following manner (McLachlan 1992): A sample is drawn from a population and a partition of this sample in two classes, males and females, is known. Using some variables, an allocation rule is established in order to classify other elements of the previous population. An underlying assumption of this procedure is that the learning sample is representative of the population, i.e. its parameters about the predictive features are statistically not different from the ones of the population.