No abstract

Researchers may reduce the numbers of haematophagous ectoparasites in nest boxes of cavity-nesting birds by removing old nests from boxes and, as a result, eliminate an important selective pressure that could influence the results from nest-box studies of birds. We recorded the numbers of parasites in tree swallow (Tachycineta bicolor) boxes in which we manipulated the presence, amount, and quality of old nests. Bird fleas (Ceratophyllus idius) were more numerous in boxes with old nests, and there was a positive correlation between nest volume and flea numbers. In one year, there was a positive association between fowl mite (Ornithonyssus sylviarum) numbers and nest volume; otherwise, fowl mites and blow flies (Protocalliphora sialia) were equally numerous in all nest types. We conclude that ectoparasites whose over-winter survival depends on old nests are more numerous in boxes with old nests, whereas parasites whose over-,winter survival is independent of old nests infect nest sites randomly. Also, reinfection and nest microclimate likely contributed to variance in parasite numbers between nest types and years, respectively. We recommend caution when speculating about the possible effects of cleaning boxes on parasites that occur in nests because different species of parasites are not influenced similarly by old nests.RCsumC : Les chercheurs peuvent diminuer le nombre d'ectoparasites hematophages dans les boites a nids de leurs oiseaux en captivite en enlevant les vieux nids des boites, Climinant ainsi une importante pression de selection susceptible d'influencer les resultats de leurs etudes ulterieures. Nous avons dCnombrC les parasites chez les Hirondelles bicolores (Tachycineta bicolor) nichant dans des boites oh la presence, la quantite et la qualit6 des vieux nids avait etC manipulee. Les puces Ceratophyllus idius se sont avCrCes plus nombreuses dans les boites contenant des vieux nids et il y avait une corrClation positive entre le volume des nids et le nombre de puces. Au cours d'une annee, nous avons observe une association positive entre le nombre d'acariens Ornithonyssus sylviarum et le volume des nids, mais, ce cas mis a part, les acariens et les calliphores Protocalliphora sialia etaient Cgalement nombreux dans tous les types de nids. Les ectoparasites dont la survie en hiver est reliee aux vieux nids sont plus nombreux dans les boites contenant des vieux nids, alors que les parasites dont la survie en hiver est independante de la presence de vieux nids sont repartis aux hasard a tous les sites de nidation. De plus, les cas de reinfection dans les nids ont probablement influence la variance dans le nombre de parasites d'un type de nid a l'autre et le microclimat, la variance du nombre de parasites d'une annee a l'autre. Les effets possibles du nettoyage des boites a nid sur les parasites peuvent donc varier puisque differentes espkces de parasites reagissent differemment a la presence de vieux nids. [Traduit par la Redaction]

ABSTR•CT.-In natural cavities, old nest material accumulates with successive use, thereby reducing the size of the cavity, and allowing the numbers of certain haematophagous ectoparasites to increase. For this reason and because researchers studying birds breeding in nest boxes typically remove old nests from boxes, the results of such studies have been questioned. The accumulation of old nest material might affect nest-site selection and nest building by hole-nesting birds, so we tested this hypothesis by manipulating the presence and amount of old nest material in nest boxes of Tree Swallows (Tachycineta bicolor). Our experiment also allowed us to examine whether costs are incurred by females due to nest building in terms of their subsequent reproductive output. When a choice of boxes was available, swallows preferred empty and clean boxes, or those where the old material had been microwaved, over those with old, untouched material. Clean boxes and those with microwaved material had more space inside, so our experiments support two hypotheses: swallows avoid potentially high numbers of parasites in nests with old material; or they prefer large cavities. Empty boxes affected nest building. The mass and volume of nests built in clean boxes were greater than for nests built on old material. Females did not add more feathers to the nest lining in boxes with old material as compared with clean boxes. Correlation analyses suggested that females building large nests began egg laying earlier in both years. Otherwise, there were no associations between the sizes of nests built by females and subsequent reproductive output (e.g. clutch size) or nestling size (e.g. body-condition index). Our results show that the common habit of removing old nests from boxes can affect nest-site choice and nestbuilding behavior. Nest building does not influence reproductive output by Tree Swallows.

No abstract

Sympatrically growing species of Drosera were examined, including rosette forms, climbers and upright, self-supporting species, in southwestern Australia, to see whether the height above ground of the capturing leaves influenced the kinds of prey caught. The leaves examined for invertebrate prey remains were all collected at the same time and the results thus represent a snapshot of the prey situation. Although the number of fully opened, active leaves and leaf size among species varied 40-fold and 22-fold, respectively, total catch per unit leaf area was relatively constant, regardless of growth form. Growth form was strongly correlated with the kinds of prey caught. Prostrate species caught mainly walking, non-aerial prey, while self-supporting and climbing species caught predominantly aerial prey.