Body Condition and Breeding of Urban Red Squirrels: Comparison of Two Populations Affected by Different Levels of Urbanization

Abstract

The red squirrel is among the mammals that have adjusted well to urban habitats. Here, we focused on the two populations inhabiting Warsaw: in a park (with year-round supplemental feeding) and in an urban forest. We hypothesised that park squirrels would have higher body mass (and better body condition), being more stable over the year, and would have a higher breeding rate (i.e., the share of breeding females). Contrary to our hypothesis, forest squirrels were heavier and had better body condition than park squirrels. The body masses of squirrels from both areas were quite stable (with the highest values obtained in spring). Females in better body conditions were more likely to breed. More breeding females and sub-adults were trapped in the park. Regardless of the study site, the highest share of breeding females was in spring, but they also bred in winter and in the remaining seasons. The lower body mass/condition of park squirrels may be possibly explained by high intraspecific competition, or by stable food (and thermal as typical for the city) conditions, in which accumulating fat was not crucial. Mild winter conditions may have also enabled squirrels to breed early. This study showed the high plasticity of red squirrels living in human-transformed habitats.

The impact of urbanisation on chipmunks, arboreal and flying squirrels: a global systematic review

“…A contrasting pattern was reported for body mass and body condition of Eurasian red squirrels in two urban areas: a park located in the city centre of Warsaw and an area described as an urban forest (Beliniak et al. 2022). Squirrels were heavier with better body conditions in the urban forest, although supplemental feeding was present only in the other study area.…”

“…Authors suggested that lower mass in the park could be due to the reduced necessity for individuals to accumulate fat where they have year‐round access to food or, since in urban park population density was greater, to increased intraspecific competition (Beliniak et al. 2022).…”

“…Comparing reproductive success (proportion breeding females, proportion young trapped or observed) on Eurasian red squirrels between urban park and urban forest in Warsaw (Poland), Beliniak et al. (2022) documented a positive effect of body condition on the probability to produce offspring in both study sites. In the urban park, there was a more extended breeding season, and again, more reproducing females and higher density than in the urban forest (Beliniak et al.…”

“…Squirrels were heavier with better body conditions in the urban forest, although supplemental feeding was present only in the other study area. Authors suggested that lower mass in the park could be due to the reduced necessity for individuals to accumulate fat where they have yearround access to food or, since in urban park population density was greater, to increased intraspecific competition (Beliniak et al 2022).…”

“…These papers suggested that, next to intrinsic factors (e.g. genotype, basal metabolic rate), not only urbanisation level but also habitat characteristics of the urbanised areas can influence variation in body mass in different tree squirrel and chipmunk species (Lyons et al 2017, Beliniak et al 2022, Wist et al 2022.…”