A model to search for birth probabilities of mammal populations using fertility data / Um modelo para busca por probabilidades de nascimentos de populações de mamíferos utilizando dados de fertilidade

A model was constructed to predict monthly birth probabilities using mammalian fertility data. We used a sample of 147 female capybaras (Hydrochoerus hydrochaeris) hunted on a farm on Marajó Island, Brazil. In the model each month was treated as a multinomial with six cells representing the six possible reproductive states (five months gestation). A hypothesis test was carried out to see whether a cosine curve would fit the birth probabilities. The results offer no support for a seasonal component (F2,9 = 1.84, P = 0.21), whereas results from a direct census do (F3,23 = 87.29, P < 0.01). Some hunting techniques were biased towards killing pregnant females (χ(2)1= 7.2, P< 0.01), thereby spreading reproduction throughout the year (F2,9 = 1.84, P = 0.21). The model remained a powerful predictive tool to be used with mammalian fertility data as long as the data are not biased towards pregnant females.

Um modelo foi desenvolvido para predizer as probabilidades de nascimentos mensais utilizando dados de fertilidade de mamíferos. Utilizamos uma amostra de 147 fêmeas de capivaras (Hydrochoerus hydrochaeris) caçadas em fazenda da Ilha de Marajó, Brasil. Cada mês foi tratado no modelo como um multinômio com seis células representando os seis possíveis estados reprodutivos (cinco meses de gestação). Um teste de hipótese foi realizado para avaliar se uma curva cossena se ajustava às probabilidades de nascimentos. Os resultados não apoiaram um componente sazonal (F2,9 = 1,84, P = 0,21), enquanto houve apoio por parte dos resultados de censo direto (F3,23 = 87,29, P < 0,01). Algumas técnicas de abate eram tendenciosas ao abate de fêmeas prenhas (χ(2)1 = 7,2, P < 0,01), consequentemente dispersando a reprodução por todo o ano (F2,9 = 1,84, P = 0,21). O modelo continuou como uma poderosa ferramenta de previsão para uso com dados de fertilidade de mamíferos, desde que os dados não se encontrem tendenciosos para fêmeas prenhas.

Differences in food preferences between individuals and populations of domestic cats Felis silvestris catus.

The food preferences of 64 cats, of which 28 were domestic pets and 36 were free-ranging animals on three farms, were tested using five food types; a sixth type was also tested on the farm cats. Information was also gathered on the background diet of the house cats (individually) and of each farm cat colony. Consistent differences were found between the predefined groups of cats in their preferences for three foods, Hard Dry (HD), Canned Meat (CM) and Raw Beef (RB), the greatest differences being between house cats and farm cats as a whole. The three colonies of farm cats showed distinct differences in preference, for RB and/or CM, and for the sixth food, Soft Dry (SD). Differences between farms could be explained by a reduced preference for items similar to major components of the background diet of each colony, i.e. selection in favour of foods that were temporally rare. Differences between house and farm cats, and within the house cats, could not be explained in this way; the house cats were neophobic towards RB, and the farm cats ate little of the HD food, possibly because they found it difficult to ingest.

Individual differences in den maintenance effort in a communally dwelling mammal: the Eurasian badger.

Group living has potential costs in terms of relative fitness for individuals that invest effort in activities providing general benefit, if other competing individuals exploit those activities and accrue similar benefits at no cost. We examined the roles of individual badgers, Meles meles, in the den maintenance activities of digging and bedding collection at their communal setts. Twenty per cent of adults and yearlings were responsible for 60-90% of the observed digging and bedding collection effort. Overall males tended to dig more than females, while durations of bedding collection were similar. Among adult and yearling males and females, individuals with a high percentage of days observed at the sett (high site fidelity) performed more digging and collected more bedding than transients and badgers of low site fidelity. Males of high status (large, mature, frequently copulating individuals) were more likely to dig than males of low status. Principal component analysis indicated negligibly low correlation between status and site fidelity for males. We hypothesize that while highly resident adult females benefit from extending the sett to avoid direct reproductive competition, males of high status and site fidelity might extend the sett to encourage receptive breeding females in their home group to stay and/or to improve survivorship of sired litters. Other categories of individual depend on the sett for shelter but, perhaps having less to gain from extending it, adopt a less active role in sett maintenance. Copyright 1999 The Association for the Study of Animal Behaviour.

The response of water voles, Arvicola terrestris, to the odours of predators.

We investigated the response of water voles to the odours of predators in outdoor enclosures. Water voles were given access to two food cages, one containing the odour of a predator and the other containing no odour, and were videotaped for 22 h. Sheep odour was also used as a control for novel odour. The predators were American mink, Mustela vison, and brown rat, Rattus norvegicus. There was no difference in the voles' response to sheep odour and no odour. The voles entered the treatment cages containing the mink's odour significantly fewer times than they entered the control cages, indicating avoidance of the former. They also gathered less food from, and stayed a shorter time inside, the treatment cages. The voles avoided the mink's odour more than the rat's odour. The fact that the experimental animals had not had previous contact with American mink suggests that the response is innate. These results also suggest that water voles perceived mink as a greater risk than rats, although they avoided odours of both these species. Copyright 1999 The Association for the Study of Animal Behaviour.