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Over the last decades, aerial insectivorous birds have been declining in both North America and Europe. Those declines have been hypothetically attributed to a decrease in prey availability caused by agricultural intensification, but empirical evidence remains scarce. Here, we quantify the effect of landscape composition on the abundance and diversity of potential prey of Tree Swallows (Tachycineta bicolor (Vieillot, 1808)) and on nestling diet in southern Quebec, Canada. We collected food boluses from nestlings and compared their composition with spatiotemporally corresponding samples from traps on farms distributed along a gradient of agricultural intensification. The diet of nestlings was mostly composed of Diptera, both in biomass and abundance, but by mid-June, these decreased with increasing proportions of intensively cultivated crops within 500 m of the nests. Trap catches for Diptera and all arthropods combined followed the same trends. Yet, the associations between Diptera subgroups (Nematocera, non-schizophoran Brachycera, Schizophora (Calyptratae), and Schizophora (Acalyptratae)) and landscape composition differed between traps and boluses, suggesting that prey selection was altered by agricultural intensification. Our results suggest that agriculture can alter the availability of preferred prey for aerial insectivores, and further studies should evaluate the impact of prey availability to explain the decline of aerial insectivores. Key words: aerial insectivorous bird, arthropods, agricultural intensification, Diptera, redundancy analysis (RDA), Tree Swallow, Tachycineta bicolor. Depuis quelques decennies, les oiseaux insectivores aeriens sont en declin en Amerique du Nord et en Europe. La diminution de la disponibilite de proies dans l'environnement causee par l'intensification agricole est souvent l'hypothese suggeree pour expliquer ces declins, mais les preuves empiriques le confirmant sont rares. Cette etude quantifie l'effet de la composition du paysage sur l'abondance et la diversite des proies potentielles de l'Hirondelle bicolore (Tachycineta bicolor (Vieillot, 1808)) tout comme sur la diete des oisillons dans le sud du Quebec (Canada). Des becquees alimentaires ont ete prelevees a des oisillons et leur composition a ete comparee a celle d'echantillons recoltes par des pieges a insectes installes le long d'un gradient d'intensification agricole. La diete des oisillons etait majoritairement composee de dipteres tant au niveau de l'abondance que de la biomasse, mais des la mi-juin, ces parametres diminuaient a mesure qu'augmentait la proportion des cultures intensives dans un rayon de 500 m des nids. Les memes relations ont ete trouvees pour les echantillons des pieges a insectes en ce qui a trait aux dipteres analyses seuls, mais aussi pour tous les arthropodes combines. Les associations entre les sous-groupes de dipteres (nematoceres, brachyceres non-schizophores, schizophores (Calyptratae) et schizophores (Acalyptratae)) et les composantes du paysage agricole differaient cependant entre les becquees alimentaires et les pieges a insectes suggerant que la selection des proies est influencee par l'intensification agricole. Nos resultats suggerent donc que l'agriculture peut alterer la disponibilite de proies pour les insectivores aeriens, mais d'autres etudes devraient toutefois etre effectuees afin d'expliquer l'effet de la disponibilite de proies dans le milieu sur le declin des insectivores aeriens. Mots-cles: oiseau insectivore aerien, arthropodes, intensification agricole, dipteres, analyse de redondance, hirondelle bicolore, Tachycineta bicolor., Introduction Anthropogenic environmental changes are affecting a large number of species worldwide and in many cases result in their decline (Fuller et al. 1995; Wittmer et al. 2007; Cahill et [...]

Breeding birds require high Levels of energy and certain nutrients, such as calcium. The extent to which calcium limits reproduction in wild birds is unclear. We performed a supplementation experiment to determine whether calcium limits the reproductive output of free-ranging insectivorous Tree Swallows (Tachycineta bicolor), a species whose usual diet contains little calcium. Providing supplemental calcium in the form of crushed oyster shell did not affect clutch initiation date, but it caused birds that had not started constructing a nest when we first detected them on the study area to begin laying sooner, which suggests that calcium reduced the length of the prelaying period. Supplemented females produced larger eggs, and that effect was most pronounced among females in good body condition. There was a trend for supplemented birds to produce larger clutches, and their clutches had significantly greater total mass than those of control birds. Supplemented birds, in particular those breeding late in the season, also hatched significantly more eggs. Our results suggest that calcium availability may limit some aspects of avian reproduction, even in nonacidified landscapes like our study area, where levels of calcium in the soil are high. Received 8 September 2003, accepted 23 September 2004. Key words: calcium limitation, clutch initiation date, clutch size, egg size, hatching success, nutrient limitation. Durante la epoca reproductiva, las aves requieren niveles altos de energia y de ciertos nutrientes como el calcio. La importancia del calcio como limitante de la reproduccion de Las aves silvestres no esta claramente establecida. En este estudio realizamos un experimento de suplementacion para determinar si el calcio limita el rendimiento reproductivo de golondrinas silvestres Tachycineta bicolor, una especie insectivora cuya dieta usual contiene poco calcio. La provision de calcio suplementario en forma de conchas de ostra maceradas no afecto la fecha de iniciacion de las nidadas, pero causo que aves que no habian empezado a construir un nido cuando las detectamos por primera vez empezaran a poner huevos mas temprano, lo que sugiere que el calcio redujo la duracion del periodo pre-postura. Las hembras que recibieron calcio suplementario produjeron huevos mas grandes, un efecto que fue mas pronunciado en las hembras con buena condicion corporal. Existio una tendencia a que las aves que recibieron calcio suplementario produjeran nidadas mas grandes y sus nidadas tuvieron una masa total significativamente mayor que las de las aves control. Las aves que recibieron el suplemento, en particular las que se reprodujeron tarde en la epoca reproductiva, tambien presentaron significativamente mas huevos eclosionados. Nuestros resultados sugieren que la disponibilidad de calcio puede limitar algunos aspectos de la reproduccion de las aves, aun en paisajes no acidificados como nuestra area de estudio, donde los niveles de calcio en el suelo son altos.

Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were compared to invertebrate availability as measured by aerial tow nets. The majority of the biomass in the nestlings' diet was adult insects with larval stages of aquatic origin, while absolute numbers of insects of both aquatic and terrestrial origin were similar. Orders of invertebrates in the diet and available were similar in number but not in biomass. Diet showed little variation by time of day, date of sampling or the age of the nestling. The mean number of odonates in the nestling Tree Swallows' diet increased exponentially as the percentage of open water and open water + cattail marsh increased within a 400-m foraging radius. Key words: diet, foraging, insect sampling, Tachycineta bicolor, Tree Swallow.

Studies in Yellow-rumped warblers (Dendroica coronata) and Tree Swallows (Tachycineta bicolor) demonstrate their high fatty acid assimilation efficiency secondary to their distinct gastrointestinal characteristics. D. coronata and T. bicolor fed with berries coated with cetyl palmitate, bayberry wax, beeswax, and the fatty-alcohol moeity of cetyl palmitate showed fat assimilations of >90%, >80%, 50% and

MICHAEL P. LOMBARDO [1] ABSTRACT.--We collected and identified 1852 prey items from 89 boluses delivered to 62 nestling tree swallows (Tachsycineta bicolor) at 14 nests in an upland old field [...]