Luc A. Wauters

Spacing behaviour of red squirrels, Sciurus vulgaris: variation between habitats and the sexes

Abstract Home range size, range use and range overlap of adult male and female red squirrels in a coniferous and a deciduous woodland were studied using radio-telemetry. Hypotheses, concerning (1) resource predictability and territorial behaviour, and (2) sex-related and habitat-related differences in spacing strategies were tested. In both habitats males had larger home ranges than females. Range size varied seasonally, tending to increase in April–June and to decrease in winter. Both males and females had intensively used core-areas (70% of all locations) that were much smaller than their total range. Dominant males had larger ranges than subordinates, and male body weight was positively correlated with home range size. For females, range size was inversely correlated with food abundance (coniferous area) or local density (deciduous area). Core-area overlap within a sex was smaller than that between sexes. Dominant females defended exlusive core-area overlap within a sex was smaller than that between sexes. Dominant females defended exclusive core-areas against other females, while subordinates behaved as floaters or settled on the edges of the ranges of dominant females. In the deciduous woodland squirrels had larger home ranges, used significantly larger and more strongly overlapping core-areas and were more tolerant of conspecifics than in the coniferous woodland. The results support the hypotheses that (1) the predictability in time and space of food resources, and (2) sexual differences in key resources used to increase reproductive success in mammals with promiscuous or polygynous mating systems, cause differences in spacing behaviour between habitat types and between adult males and females.

Space use and dispersal of red squirrels in fragmented habitats

Eurasian red squirrels Sciurus vulgaris in fragmented woodlands had a similar spacing pattern as in large woodlands: females had intrasexual exclusive core-areas, while core-areas of males overlapped extensively with core-areas of other males and with core-areas of females. However, in fragmented woodlands, home ranges (site B) and core-areas (both study sites) were smaller than in large deciduous woodlands. Hence, space use and home range size in habitat fragments are strongly influenced by size and structure of the woodlots and, in case of small woodland patches, by the presence of connecting treerows. Juveniles had very small home ranges prior to dispersal, but home range size increased after the dispersal period

EFFECTS OF FOOD AVAILABILITY AND DENSITY ON RED SQUIRREL (SCIURUS VULGARIS) REPRODUCTION

Density-dependent reproductive rate may be the result of all individuals in a population suffering reduced fecundity when density increases (Lack 1954), or it may be the result of a lower proportion of individuals living in favorable places at high density (Andrewartha and Birch 1954). We used a key-factor analysis to investigate whether re- productive rate in two red squirrel (Sciurus vulgaris) populations was density dependent. Four k values were determined, indicating offspring mortality caused by: adult females not entering oestrus (k,), oestrous females not giving birth (k2), lactating females failing to wean offspring (k3), and mortality in litters of successful females (k4). We also investigated the effect of food availability on the different k values and tested predictions of the two contrasting hypotheses (Lack vs. Andrewartha and Birch) by examining the mechanisms of density dependence. The reproductive performance of female squirrels was monitored over 18 breeding sea- sons in a coniferous forest and over 16 breeding seasons in a deciduous forest. In the coniferous forest, annual variation in pine seed abundance only affected k4, which was only weakly related to total mortality of offspring (K). In the deciduous woodland, however, the key factors k2 and k3, which were strongly related with total K, were inversely correlated with food abundance. In the coniferous forest, only k2 was female density dependent, and breeding failure before parturition occurred primarily among floaters, which were more numerous at high density. In the deciduous forest, annual and seasonal variation in the number of floaters caused density dependence in fecundity (k,). Increased breeding failure of lactating females (k3) with high female density was positively correlated with the number of floaters and with the proportion of females occupying poor quality home ranges. We concluded that density-dependent reproduction in red squirrels can be caused by two mech- anisms: a direct density effect of more floaters at high female density, and an effect of habitat heterogeneity, with more females occupying poor territories at high densities, re- sulting in low breeding success. That reduced fecundity or breeding failure at high densities occurred mainly in female squirrels not occupying good territories, and that annual and seasonal variation in litter size of successful females was not density dependent, supported the predictions of the Andrewartha and Birch (1954) hypothesis.

Lifetime Reproductive Success and Its Correlates in Female Eurasian Red Squirrels

Individual variation in lifetime reproductive success (number of weaned offspring in a lifetime) of female red squimels was studied in two populations in North Belgium for 8 yr. Fitness, the number of reproducing offspring, was calculated combining expected survival to reproductive age of dispersing young and reproductive performance of local recruits. Of 66 resident females, 20 (30%) never produced young. 89% of territorial females had offspring, while all non-territorial females failed to reproduce. Lifetime reproductive success of mothers (females that produced at least one weaned young) averaged 5.04 young (range 1-11), fitness averaged 2.07 (range 0.26-4.44). Both measures of reproductive success were strongly correlated (R 2 =0.73). Variation in fitness and lifetime reproductive success was mainly the consequence of variation in the number of litters produced. Variation in body condition, foot length (size) and territory quality explained 50% of variation in the number of litters. Variation in the number of young/litter, age at first breeding and year of birth were not significantly correlated with variation in lifetime reproductive success. We conclude that large, heavy females that established home ranges in food-rich areas live longer and produce more young than lighter, shorter-lived females living in poorer territories. and discuss the occurrence of chance-events affecting reproductive output in young and old squirrels

Interspecific effects of grey squirrels (Sciurus carolinensis) on the space use and population demography of red squirrels (Sciurus vulgaris) in conifer plantations

Interspecific competition between red squirrels and grey squirrels was investigated by comparing the population demography, spacing behavior and habitat use of red squirrels in two large conifer plantations in northern England: one site had only red squirrels (the ‘red-only’ site), in the other both red and grey squirrels occurred (the ‘red–grey’ site). Despite more abundant food at the red–grey site, red squirrel densities (0.26 ha−1 at the red–grey site, 0.29 ha−1 at the red-only site), adult survival rates and the breeding rates of females were similar at both study sites. Grey squirrels at the red–grey site occurred at higher densities (0.92–1.1 ha−1) than did the reds and tended to have higher breeding rates. In the presence of grey squirrels, the recruitment pattern of red squirrels changed and there was little recruitment of subadults. The juvenile recruitment rate in the red–grey site (13%) was much lower than in the red-only site (50%). Grey squirrels, in contrast, had higher juvenile recruitment rates at the red–grey site (41%). The core areas of the home ranges of red squirrels in the red–grey site were more strongly overlapped by grey squirrels than by conspecifics. Red squirrels did not select the habitat with the best tree seed crop (Scots pine) but preferred dense Sitka spruce plantations; they appeared to avoid the Scots pine area with its high grey squirrel density. Data on foot length and body condition indicated decreased body growth in young red squirrels when grey squirrels were present. Our data suggest that adult red squirrels suffered little from interspecific competition with grey squirrels and that the key factor is decreased juvenile recruitment in red squirrels.

The Effects of Habitat Fragmentation on Demography and on the Loss of Genetic Variation in the Red Squirrel

A major problem in conservation biology is the extent to which the loss of genetic variability in isolated populations reduces their chance of survival. We present data in which the loss of genetic diversity in small and isolated populations can be directly related to population dynamics. Genetic similarity in red squirrels is inversely correlated with population size. The loss of genetic variation and the lower population densities in isolated populations are both the result of reduced immigration. Our data suggest that population processes rather than genetic problems are the real threat to small squirrel populations.

Immigration pattern and success in red squirrels

SummaryWe studied the characteristics of immigrants and the effects of immigration on reproductive activity and spacing behaviour in red squirrels living in high-quality woodlands. Male immigration peaked in spring, female immigration in autumn. There was no sex bias in dispersal distance of local recruits or in the proportion of male/female immigrants, but more subadults than adults immigrated on the study plots. Hence, hypotheses explaining sex-biased dispersal were irrelevant in explaining immigration patterns in our study populations. Immigrant females were not in breeding condition, nor had they produced a litter prior to immigration. Hence breeding dispersal did not occur. Red squirrels are promiscuous, and females defend intrasexual territories while males have overlapping home ranges with a dominance hierarchy (Wauters et al. 1990; Wauters and Dhondt 1992). Site fidelity is very important to reproductive success and most parents still have a high residual reproductive value after having produced a litter. Under such circumstances, the resident fitness hypothesis (RFH; Anderson 1989) predicts that parents can benefit by forcing emigration of offspring if the latter are likely to find nearby vacancies. The settlement pattern of successful immigrants, which had a higher probability of becoming established when they had high body mass and when they were settling in plots with reduced intrasexual competition, agreed with the RFH and with the proximate dispersal mechanism suggested by Gliwicz (1992), that dispersal tendency in both sexes depends on the degree of intrasexual competition under local conditions. The fact that close inbreeding was never observed could indicate that random immigration of both sexes, within the social environment of a partly territorial, relatively long-lived species, has evolved not only to reduce competition for resources between parents and offspring but also as an inbreeding avoidance mechanism.

Do female roe deer in good condition produce more sons than daughters

In polygynous roe deer Capreolus capreolus, males are only slightly heavier than females and the overall sex ratio at birth is close to unity. We studied offspring sex ratio and litter size (range 1–4, n = 74) of culled females, in utero, which provided an opportunity to examine responses of sex ratio to maternal condition. Male embryos were heavier than their sisters, and male fawns (9 months old) heavier than female fawns, suggesting a higher growth rate in males. There was no evidence for differential mortality between the sexes from birth to 9 months old. Heavier adult females produced larger embryos than lighter, or primiparous females. The overall sex ratio of embryos did not differ from unity, but adult does had more male embryos (55%) than primiparous does (32%), and the proportion of male embryos in a litter increased with the mothers body mass. Litter size also tended to increase with maternal age and body mass. We argue that this pattern reflects adaptive variation in offspring sex ratio.

Interspecific competition between native Eurasian red squirrels and alien grey squirrels: does resource partitioning occur?

Abstract. In heterogeneous environments, differential niche selection by two competing species will result in niche partitioning so that individuals of each species can maximise their fitness under different sets of environmental variables. Thus, niche partitioning is considered essential to allow co-existence of ecologically related species. To assess whether niche partitioning was occurring between native red squirrels and alien grey squirrels living together in a 13-ha high-quality mixed deciduous woodland in north Italy, we investigated temporal and spatial patterns in their activity and foraging behaviour between 1996 and 1998. We used live trapping and radio-tracking to study numbers, distribution and behaviour of squirrels. Daily and seasonal temporal activity patterns, and activity on the ground and in the trees, were similar in the two species. However, grey squirrels were more tree specialists and had a narrower tree-species niche width than red squirrels, in particular making greater use of oak. Other studies of red and grey squirrels in allopatry show that the two species differ in the extent they utilise oak. Overall, tree-species niche overlap was about 70%. Grey squirrels had larger home ranges than red squirrels. Home ranges and core areas of both species were larger in males than females. Also, intraspecific home range and core-area overlap patterns were similar to those found in allopatric populations of these species. Overall, there was no evidence that the use of space of one species was affected by the other. Our results show that there was no niche partitioning of activity or foraging behaviour in time or space during the study. This suggests that, at moderate grey-squirrel densities, red squirrels are unable to avoid competition with grey squirrels, and that competition for food and/or space will occur when these resources become limiting.

Body mass at weaning and juvenile recruitment in the red squirrel

This paper describes the factors affecting local recruitment of juvenile red squirrels, Sciurus vulgaris L., in a coniferous and a deciduous woodland. It also investigates which factors affect body mass at weaning (10-12 weeks old). In a 4-year study, of 85 weaned juveniles from 53 different nests, heavy young were more likely to be recruited in the study areas than lighter young. More young born early in a breeding season were recruited than young from later nests, but there was no difference in recruitment rate between juveniles from spring and summer litters. Differential local recruitment by body mass at weaning occurred from weaning to 6 months after birth (when the period of natal dispersal and heavy early mortality is finished)