The social organisation of a population of Microtus agrestis was studied by trapping and radiotracking in southern England. There was no significant variation in male home-range size during the breeding season or between years but there was significant variation in core areas between years but not during the breeding season. There was no significant relationship with male density and core area ...

A common feature of many birds breeding in seasonal environments is that fitnessrelated parameters such as nestling mass or survival decline as the breeding season progresses. Consequently, there is a tendency for early breeders to have better reproductive performance than individuals breeding later in the season. This variation could be caused by factors associated with the date of laying, suc...

Competition elevates plasma testosterone in a wide variety of vertebrates, including humans. The 'challenge hypothesis' proposes that seasonal peaks in testosterone during breeding are caused by social challenges from other males. However, during experimentally induced male-male conflicts, testosterone increases only in a minority of songbird species tested so far. Why is this so? Comparative e...

In seasonallybreeding birds, natural selection favors individualsthat begin breeding earlier in a year because they produce more or higher quality offspring than those that begin breeding later. Among the factors that in uence the timing of breeding, which include the age, health, competitive ability, or mate quality of individuals, is the longevity of the pair bond, with birds that remain mat...

Density-dependent competition for food resources influences both foraging ecology and reproduction in a variety of animals. The relationship between colony size, local prey depletion, and reproductive output in colonial central-place foragers has been extensively studied in seabirds; however, most studies have focused on effects of intraspecific competition during the breeding season, while lit...

Understanding the factors influencing the degree of spatial overlap among conspecifics is important for understanding multiple ecological processes. Compared to terrestrial carnivores, relatively little is known about the factors influencing conspecific spatial overlap in snakes, although across snake taxa there appears to be substantial variation in conspecific spatial overlap. In this study, ...

Multiparous Suffolk and Suffolk-cross ewes were randomly allotted to treatments within breed and year to measure effects of ram exposure, during transition from anestrus to breeding activity, on reproductive performance. Treatments were: 1) ewes joined with two mature vasectomized Rambouillet rams for 15 d before breeding (DC), 2) ewes maintained across a net wire fence from two vasectomized ra...

Age-dependent reproductive timing has been observed in females of a number of species; older females often breed earlier in the season and experience higher reproductive success as a result. However, to date, evidence for within-season variation in reproductive effort (RE) for males has been relatively weak. Males are expected to time RE in light of intraseasonal variations in the availability ...

BACKGROUND In species with biparental care both members of the breeding pair cooperate to raise the offspring either by assisting each other in every reproductive task or by specializing in different ones. The latter case is known as reproductive role specialization. Raptors are considered one of the most role-specialized groups, but little is known about parental behavior away from the nest. U...

The experiments which have provided insight into the role of the pineal gland and melatonin in sheep reproduction are reviewed. There is now strong evidence that timed daily melatonin administration and continuous administration via implants are equally effective in promoting the same physiological consequences as short daylength. Thus melatonin treatments lasting six weeks can result in an adv...