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

SIMPLE SUMMARY: The red squirrel is among the mammals that have adjusted well to urban habitats. We compared two populations inhabiting Warsaw: in a park (with plentiful supplemental feeding) and in a forest (with no feeding and restricted visitor access). In previous studies, we showed that squirrels in the park differed from forest squirrels in space use, food choice, activity patterns and interactions with people. Now, we predicted that the supplemental feeding of park squirrels would result in their higher body mass, better body condition, a higher share of breeding females and extended breeding season. Contrary to our assumptions, forest squirrels were heavier and had better body conditions. Yet, in both populations, better body conditions increased chances for breeding. There were more breeding females and more young squirrels in the park. Squirrels from both areas bred mostly in spring but also in winter. The lower body mass/condition of park squirrels may have been due to competition in a high-density population, or may suggest that with year-round access to food, accumulating fat was not crucial. The extended breeding season may have been thanks to good feeding conditions and/or mild winters in the city. Again, we showed the high plasticity of red squirrels living in human-transformed habitats. 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.