pregnancy rate is one of the most important factors determining profit or loss. Considerable emphasis and focus is placed on the nutritional and reproductive management of the cow herd; but, unfortunately, in most operations little emphasis is placed on the bull. However, each bull is expected to impregnate from 15 40 females during the breeding season in a typical cow-calf operation and, thus,...

The cycle of gonad development and related changes in the length structure and spatial-temporal distribution of ninespine sticklebacks (Pungitius pungitius L.) in Puck Bay were studied. Observations were carried out in the shallow shore zones, as well as in the deeper epipelagic zone of the Bay. Ninespine sticklebacks reproduce in the brackish environment of Puck Bay, breeding in its warmer, in...

Surveys to detect the presence or absence of endangered species may not consistently cover an area, account for imperfect detection or consider that detection and species presence at sample units may change within a survey season. We evaluated a detection–nondetection survey method for the federally endangered golden-cheeked warbler (GCWA) Dendroica chrysoparia. Three study areas were selected ...

The seminal vesicles of adult sand rat contain a major secretory protein band (MW 21 kDa) designated as Psammomys obesus seminal vesicles protein of 21 kDa (POSVP(21)). This protein is abundant in secretions, regulated by androgens and also present in the vaginal plug. POSVP(21) accounts for over 22.3% of soluble proteins from homogenate during the breeding season, 13.3% during the middle seaso...

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...

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...

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 ...

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...

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, ...