The annual energy budget of a weasel population in farmland near Newburgh, Aberdeenshire, was studied for two years. Data on population dynamics were collected by live-trapping weasels, and data on metabolism were obtained from laboratory experiments. Fifty four male and 24 female weasels were trapped 623 times, and the sex ratio of both individuals and captures was significantly different from 1:1. Females had a lower trappability than males, which probably concealed an equal sex ratio in the population. The numbers of females on the study area were calculated from male numbers on the basis of an equal sex ratio. Most weasels (23) were present in late summer, and the average density was one weasel/7.7 ha. Most males were residents and were caught regularly, but the residential status of females was difficult to determine. Weights of trapped weasels varied widely, but tended to decline between summer and mid-winter. Few breeding data were collected. Analysis of scats from trapped weasels showed that small rodents, especially short-tailed voles, were the most frequent prey. As temperature decreased the average daily metabolic rate (ADMR) of both sexes increased, with a relatively greater rise for females; ADMR was also influenced by body weight and activity. Elongate mustelids have higher metabolic rates than normally-shaped mammals of similar weight. Regressions of ADMR on temperature were significantly different for males and females, that for females having the steeper slope. Females ate relatively more each day than males : mean daily consumption was 0.33 g/g/day for males and 0.36 g/g/day for females. Daily faecal production and the energy lost in faeces and urine were influenced by the proportion of indigestible material consumed; on low-bulk diets weasels lost as much energy in urine as in faeces. Assimilation efficiency was reduced by up to 10% on bulky diets; the range for four foods was 73-83% for males, and 76-83% for females. In 1972-73 minimum estimates of the standing crop, energy flow, and annual energy budget were lower than in 1971-72. Energy flow was greatest in summer, and least at the end of winter, and averaged 3865 kcal/ha/yr; mean annual consumption was 4930 kcal/ha/yr. The seasonal consumption of six major food types was calculated, and minimum estimates were obtained of the numbers of small rodents eaten. Factors favouring selection of sexual dimorphism were discussed, and a new hypothesis, that sexual dimorphism is advantageous for breeding females, was presented. Calculations for weasels showed that small females when breeding required daily 20% less energy than did hypothetical 'male-sized' females. Data on movements and dispersion were presented in Appendix 2. During the breeding season the winter territorial system of males broke down, and their movements were greatest. The seasonal dispersion of males was described, but there were few data for females. The average size of male territories was 13.3 ha.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:593158 |
| Date | January 1975 |
| Creators | Moors, Philip J. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU409442 |
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