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Clutch overlap is a reproductive strategy of the Feral Pigeon, which results in an increase in the number of clutches produced by a pair and, as follows, an increase in the number of young raised. It is dependent on the length of time the clutch is cared for and the length of the interval between clutches. Both these component elements of clutch overlap are directly affected by environmental conditions, such as the length of day and ambient temperature. The duration of clutch care and the clutch interval were distinctly shorter in the warmer part of the year with a longer day than during the fall and winter. We believe that ambient temperature has a significant effect on the length of the clutch interval, as it is a decisive factor in the achievement of thermoregulation ability in the nestlings. Earlier achievement of this ability by nestlings in higher ambient temperatures (at Ta = 21.5°C, normothermy appeared in the 6th to 7th post-embryonic day in the life of nestlings, while at Ta = 19.5 °C – in 8–9 days) allows both parents to forage for longer periods of time and to start a new breeding cycle earlier. We confirmed that nesting conditions (the number of nests in a breeding pair's territory, brood size and location of the nest in the colony) also influenced the duration of clutch care and the length of clutch interval, and therefore, the degree of clutch overlap. The clutch interval was shorter when parents only cared for one young, than when two young were in the nest. Breeding pairs with large territories that included two nests had shorter clutch intervals than those pairs with only one nest. Young raised in nests located close to egresses left the colony more quickly than young in nests farther away
Twelve biochemical values of the serum (concentrations of sodium, potassium, calcium, glucose, urea nitrogen, creatinine, total protein, and enzyme activities of ALP, CPK, AspAT, A1AT, amylase) were determined for 102 bison Bison bonasus (Linnaeus, 1758) coming from the free-ranging population of the Białowieża Forest and from the breeding enclosure. The animals were culled in the winter periods of 2000/2001 and 2002/2003. In adult males only the activity of A1AT is significantly higher than in adult females. The remaining values do not differ significantly between the sexes in any of the three age groups (I - calves, II - youngsters, III - adults). Also, no significant differences in serum parameters were observed between healthy males and the ones exhibiting symptoms of posthitis/balanoposthitis. It was established that the following changes in the values of serum parameters are age-dependent: a decrease in potassium and glucose concentrations and the enzymatic activity of ALP, and an increase in AspAT activity. The results were compared to the corresponding data from the research carried out 20 years earlier (1980-1984) and it has been discovered that the values of seven parameters are significantly different as opposed to the previous results. The following differences were established: currently the concentrations of potassium and urea nitrogen are higher in all age groups; the concentration of glucose is higher in the groups of calves and youngsters; creatinine concentration is lower in adults; the activity of AspAT has increased in youngsters, only; the activity of A1AT has increased, and of amylase has decreased in all animals examined. The changes in the values of serum parameters were analysed in the context of data obtained from post-mortem examinations and we conclude that those changes reflect the growing number of patho- morphological changes in internal organs of the bison dissected. Changes localised mainly in the liver and lungs could be related to parasitical infestations; others were noted in kidneys and in the prepuce and penis area in the males with posthitis/balanoposthitis symptoms. In the discussion it is suggested that the deterioration of the physical condition of European bison inhabiting the Białowieża Forest may be connected to such environmental and populational factors as: winter supplementary feeding, winter aggregations, and a decline in immunity related to inbreeding.
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