Additional file 1: Table S1. of Sex-specific patterns in body mass and mating system in the Siberian flying squirrel

The best ranked models explaining body mass of male Siberian flying squirrels measured in summer and winter (upper and lower panel respectively). Columns show the variables included in each model (see main text for an explanation of the variable names), the degrees of freedom of each model, the Akaike value corrected for small sample size (AICc) and the difference in AIC between best ranked and the target model (∆AICc) as well as the AIC weight of each model. List is restricted to 10 best ranked models. Table S2. The best ranked models explaining body mass of female Siberian flying squirrels measured in summer and winter (upper and lower panel respectively). Columns show the variables included in each model (see main text for an explanation of the variable names), the degrees of freedom of each model, the Akaike value corrected for small sample size (AICc) and the difference in AIC between best ranked and the target model (∆AICc) as well as the AIC weight of each model. List is restricted to 10 best ranked models. Figure S1. Male and female body mass (least square means and standard errors) for each month from the winter model (1 January to 3 March) and for the summer model (6 June to 11 November). Only observations where the exact age was known have been used for this supporting analysis (see methods). For females, June was omitted because they may still be pregnant in June. Lines above the bars join months for which body mass was significantly different after post-hoc testing (adjusted for multiple testing using the Tukey method). For females, there were no significant differences in body mass between the months of the winter season and between the months of the summer season. (DOCX 127 kb

Spruce cone crop data

Data describes estimates of Norway spruce cone crop (unit: cones per tree, calculated from trees in research forests) in three different areas, Ullava, Oravainen and Maalahti, surrounding the red squirrel study area in Kauhava, Finland

Nest-box occupancy data for flying squirrels

Data describes occupancy (1=precence, 0=absence) of flying squirrels in nest boxes. BCODE= name of nest box. ID = a unique combination of box name and census year. Ural owl and goshawk columns describe modelled predation risk from these predators at the nest box site, see article for methods. h1...h27 refer to different land use classes and their combinations as in Table 1 of the research article. _200m and _1km means area (square meters) of that habitat within 200 meters and 1km from nest box, respectively. s (for example h17_200ms) refers to standarized amount of that habitat, see methods

Predation risk landscape modifies flying and red squirrel nest site occupancy independently of habitat amount

<div><p>Habitat choice often entails trade-offs between food availability and predation risk. Understanding the distribution of individuals in space thus requires that both habitat characteristics and predation risk are considered simultaneously. Here, we studied the nest box use of two arboreal squirrels who share preferred habitat with their main predators. Nocturnal Ural owls (<i>Strix uralensis</i>) decreased occurrence of night-active flying squirrels (<i>Pteromys volans</i>) and diurnal goshawks (<i>Accipiter gentilis</i>) that of day-active red squirrels (<i>Sciurus vulgaris</i>). Unexpectedly, the amount of preferred habitat had no effect on nest box use, but, surprisingly, both squirrel species seemed to benefit from close proximity to agricultural fields and red squirrels to urban areas. We found no evidence of trade-off between settling in a high-quality habitat and avoiding predators. However, the amount of poor-quality young pine forests was lower in occupied sites where goshawks were present, possibly indicating habitat specific predation on red squirrels. The results suggest that erecting nest boxes for Ural owls should be avoided in the vicinity of flying squirrel territories in order to conserve the near threatened flying squirrels. Our results also suggest that flying squirrels do not always need continuous old forests, and hence the currently insufficient conservation practices could be improved with reasonable increases in the areas left untouched around their nests. The results of this study demonstrate the importance of taking into account both habitat requirements and predation risk as well as their interactive effects when modeling the occupancy of threatened animal species and planning their conservation.</p></div

Nest box occupancy data for red squirrels

Data describes nest box occupancy of red squirrels. 1= presence, 0=absence. BCODE= name of the box. ID= unique combination of box name and census year. Goshawk and Ural owl columns describe modelled predation risk from these predators at the nest box site, see methods in research article. h1...h27 refer to land use classes as in Table 1 of the article. _300 and _2500 m refer to the area of each land use class within 300 meters and 2.5 kilometers from the nest box in square meters. Ending 's' (h8_300ms) refers to the standardized area. TimePeriod describes the slightly different detection probability before and since 2006

Young pine forest has a negative effect on nest box occupancy by arboreal squirrels.

<p>The effect of standardized amount of young pine forest (A) within buffers of 200 m and 1 km on flying squirrel occurrence in nest boxes, and (B) within buffers of 300 m and 2.5 km on red squirrel occurrence in nest boxes.</p

Summary of flying squirrel models.

<p>Summary of flying squirrel models.</p

Land use classes, their combinations and abbreviations.

<p>Land use classes, their combinations and abbreviations.</p

Increasing area of field first increases and eventually decreases occurrence of squirrels.

<p>The effect of standardized amount of agricultural field (A) within buffers of 200 m and 1 km on flying squirrel occurrence in nest boxes, and (B) within buffers of 300 m and 2.5 km on red squirrel occurrence in nest boxes.</p

The presence of main avian predator decreases nest-box occupancy by flying and red squirrels.

<p>The effect of (A) Ural owl (kernel height) on occurrence of flying squirrels and (B) goshawk (kernel height) on occurrence of red squirrels in nest boxes based on models at small and large spatial scale.</p