The handicap hypothesis assumes that sexual ornaments impose a viability cost upon the bearers. There have been few empirical tests of this assumption. Previous studies show evidence for the cost of a tail ornament in male birds: a negative relationship between an experimentally increased tail ornament (long tail streamers) and efficiency at foraging for nestlings. However, it must be admitted, that the apparent impairing effect of an elongated tail could be a result of a decrease in male parental effort in response to an increase of female parental effort, which might have occurred in response to increased male attractiveness (differential allocation of female parental effort). In this study, the effect of differential parental expenditure was eliminated by lengthening the tail in female, rather than male, sand martins (Riparia riparia). Tail‐elongated females decreased the rate at which they fed nestlings, and captured more but smaller insects. There was no simultaneous increase of feeding rate in the males that could explain the decrease of feeding rate in the females. These results confirm the existence of a cost of a tail ornament in birds feeding in flight, as is expressed in terms of impaired flight and foraging capacity.

Costs of a sexual ornament in its early evolutionary form and the relationship between these costs and individual condition may be an important influence in the likelihood of possible evolutionary mechanisms involved in the evolution of this ornament. We reconstructed the tail shape in hypothetical ancestors of recent hirundines (Aves: Hirundinidae), from which the elongation of tail feathers under sexual selection might have begun. By elongating the tail in sand martins (Riparia riparia, Hirundinidae), we simulated the early evolution of a long forked tail-the typical ornament of male hirundines. Birds with initial ornament captured smaller insects than controls, which suggests that this ornament imposed a cost in terms of impaired foraging. Furthermore, birds with naturally longer tails were better able to cope with initial ornament than naturally short-tailed birds. If length of tail in sand martins indicates the quality of individuals, our results suggest higher costs of this initial ornament for poorer than for higher quality individuals. We discuss the potential role of the handicap principle and other mechanisms in early evolution of a tail ornament.

No abstract

. 1994. Intra-and interspecific behaviours in bank vole and striped-field mouse under enclosure conditions. Acta theriol. 39: 29-36.Direct observations of the behaviour of bank voles CIethrionomys glareolus (Schreber, 1780) and striped-field mice Apodemus agrarius (Pallas, 1771) were carried out in semi-natural conditions (enclosure). Intra-and interspecific behaviours in both voles and mice were similar. A quick escape of animals was observed as a result of the majority of meetings (ca 70%); fights among individuals were not frequent (usually about 10% of meetings). It seems that interactions among the two studied species have agonistic character, but none of them shows a visible domination over another. If competitive interactions among bank voles and striped-field mice take place, they have a character of exploitation; direct aggressive contacts are not the most important in competition.

SummaryThe study was carried out in July 2009 in Murmansk (68°57' N; 33°03'E) and involved algae that had washed up at the edge of the intertidal zone of Kola Bay. Two areas of algae were selected for this study: uncontaminated (algae I) and algae contaminated with waste products (algae II). The material was collected using a frame with an area of 100 cm 2 . A total of 40 samples were taken. The abundance of the springtails was almost three times lower in the contaminated algae than in the uncontaminated algae, whereas the species diversity of the springtail communities was much higher in the contaminated algae. The littoral species Hypogastrura viatica was the dominant species in the uncontaminated algae, and that in the contaminated algae was the cosmopolitan species Folsomia quadriuculata. It appears that the contamination of the algae with waste products can promote the intensification of competition among springtails and between springtails and other saprophagous invertebrates.