Studies on the Hedgehog, Erinaceus europaeus L., in New Zealand

Abstract

Results of a questionnaire and reports of hedgehog deaths were analysed to reveal the course of the animal’s spread and abundance throughout New Zealand over the past 103 years. Between 1870 and 1948, hedgehog numbers increased prolifically but their population appears to have levelled off since then. Maps are presented showing the history of their spread and present day abundance. The animals are most abundant in lowland urban and closely farmed areas but occur with diminishing abundance above 800m. Hedgehogs are extremely rare or absent from regions with over 250 cm rain per year or more than 250 frosts per year. 66 hedgehog skulls from New Zealand were compared with 34 from Britain and found to be on average 2.6% shorter along the condyle-basal axis. It is suggested that this change is a response to New Zealand’s warmer climate in accordance with Bergmann’s rule. Changes in body weight and size, pelage, and the timing of dental eruption in juvenile animals is described, and the rate of dental attrition and the sequence of epiphysial fusion of the long bones studied. Early feeding and hibernating regimes profoundly affect the growth rate and eventual adult size of wild hedgehogs so measurements made on fully grown adult animals are extremely variable. 83 animals were aged by counting growth rings on the lower jaw and correlations drawn between this method and other criteria for estimating age. In the field, animals of the season can be identified by the state of dental eruption and some older animals aged by the degree of dental attrition. Growth rings, however, remain the only reliable method for aging all animals. Seasonal fluctuations in the body weight of European and New Zealand hedgehogs are compared. Road counts and nightly transects revealed that hedgehogs near Wellington hibernated for about three months each winter, compared with about four months near Palmerston North. North of Auckland, few hedgehogs are thought to hibernate at all. The proportion of animals hibernating at Lower Hutt varied from an estimated 21% in the warm winter of 1971 to 63% in the colder winter of 1972. Males generally emerged from hibernation two or three months before females. 115 animals were dissected and examined for depot fat. These deposits were not made until an animal reached. 300g and fat was laid down and used up in such a manner as to ensure that the animal remained wrapped in a layer of subcutaneous fat for as long a period as possible. Small animals carrying little fat may continue to grow and increase their weight through the winter but those failing to attain a weight of 300g or those whose weight sank below 300g stood a greatly reduced chance of surviving the winter. Hedgehogs at Palmerston North are thought to have spent longer in hibernation because they laid up more fat than those in Wellington. Results of a two year population study on a 56ha suburban area at Lower Hutt are described. 207 animals were tagged. 96 transients were not seen again. 101 animals returned to visit the area occasionally and 10 animals were recaptured often enough to indicate that they were residents living mainly in the study area. The number of hedgehogs using the study area varied from an estimated four animals in midwinter to 98 in summer. Of 315 recaptures, half were made within 300m of the point of release and 95% within 800m of the point of release. The 10 resident animals were reckoned to have home ranges of from 5ha to 26ha (mean 18ha). The home ranges of these and many other animals overlapped yet no signs of territorial behaviour were observed. Maps are presented showing favoured foci of activity and inferred pathways running between these centres of the study area. Though solitary animals for most of their lives, it is argued that they have a social organisation resembling that of free-ranging domestic cats, the main purpose of which is to disperse the members of the community and ensure that the available food is shared on the basis of time rather than space. It was concluded that the two neighbouring courses constituting the study area provided a poor marginal habitat for hedgehogs for most of the year. Large numbers arrived to exploit a temporary local supply of insect food during summer, only to quit the area for the rest of the year. It was estimated that the density of the hedgehog population on the study area varied between 0.07/ha in winter to 1.75/ha in summer - less than the estimated 2.0/ha made on dairy pasture in Palmerston North and 8.0/ha at Lincoln. Of 929 wild hedgehogs examined, 19 bore signs of self-anointing. Young animals anointed themselves when removed from their nests, possibly as a means of advertising their whereabouts to their mothers. Among adult animals, self-anointing was confined to the breeding season and often in the presence of the opposite sex. It is suggested that self-anointing may make one partner more acceptable to the other. In captivity the reaction takes the form of a displacement activity being triggered by novel odours or objects. Caparinia tripilis, the hedgehog mange mite was first recorded in New Zealand in the 1950s, when the host population is presumed to have reached its peak. 402 hedgehogs were examined for infection and the course of the disease followed in 97 recaptured tagged animals. 46% of male and 26% of female hedgehogs were found to be infected, the disease attacking adults more than juveniles. Infected females frequently recover from the mange but remissions are few among male hedgehogs. The infection often leads to secondary infection with ringworm and blowfly strike which may prove fatal. Animals infected with mange in autumn stand a reduced chance of surviving the winter. It is suggested that the infection is a major population regulator, especially in urban areas where the incidence is higher than in rural districts. 78 hedgehogs from dairy farms in the North Island were examined and 41 gave serological evidence of recent leptospiral infection. Leptospira ballum was isolated from the kidneys of hedgehogs from Eltham, Kaitaia and Ngatea where it is known to infect cattle and farmers. All but one of the infected hedgehogs appeared to be healthy. Serological evidence for infection with L. icterohaemorrhagiae, L. hyos, L. medanensis, L. andaman. L. pomona and L. canicola was also gathered. Based on the age structure of a sample of 83 hedgehogs it was estimated that their average longevity was less then 2.7 years and more probably nearer 2.0 years. The oldest animal found was 7 years of age. Compared with English figures, approximately twice as many New Zealand hedgehogs survived their first winter but they suffered their highest death rate in their second year, possibly as a result of their susceptibility to hedgehog mange.