A total of 57 hedgehogs were tracked over four winters between 2010 and 2014, comprising 34 rehabilitated (21 males, 6 females and 7 unknown) and 23 wild hedgehogs (13 females and 10 males) (Table 1). Two tags fell off soon after attachment giving 55 individuals tracked. The age profiles of hedgehogs differed between wild and rehabilitated hedgehogs, with the majority (74%) of wild hedgehogs comprising adults, whereas the majority (91%) of the rehabilitated hedgehogs were young of the year.
Hedgehogs were radio-tracked on average 133.76 ± 5.7 days (n = 55), with wild hedgehogs being tracked for significantly longer (n = 23; mean = 158.7 ± 6.89) than rehabilitated hedgehogs (n = 31; mean = 115.84 ± 7.04) (t test: t = 4.392, df = 51.50, p value < 0.001), due to the rehabilitated individuals being released throughout the winter period, compared to the wild individuals that entered the study in late autumn or early winter.
A total of 36 (63%) hedgehogs were alive at the time of tag removal and were deemed to have survived the winter. Seven (12%) individuals were known to have died during the study, comprising four wild individuals and three rehabilitated. Cause of death was attributed to road traffic accidents (n = 3, 43%), predation by badgers (n = 3, 43%) and one hedgehog (14%) was likely to have died from starvation due to a lack of fat reserves as identified at necropsy. All rehabilitated hedgehogs that died were predated by badgers. The fate of 14 (3 wild and 11 rehabilitated) hedgehogs (25%) could not be determined due to combination of tag loss/failure or the hedgehog not being recaptured. Therefore, the survival rate of hedgehogs whose fate was known was 83% (n = 42).
Kaplan-Meier survival analysis showed that hedgehog survival over winter was 0.961 ± SE 0.028 after 100 days, falling to 0.257 ± SE 0.791 after 200 days (Fig. 1). However, only 10 individuals were tracked over 181 days, reducing sample size, which resulted in lower survival probabilities towards the end of the study. There was a significant difference in overwinter survival between wild and rehabilitated hedgehogs (log rank test: chi-squared = 5.6, d.f. = 1, p = 0.017) (Fig. 2). However, the two survival curves only diverged after 150 days, in response to very few rehabilitated hedgehogs being tracked for more than 150 days. Therefore, a survival analysis on the first 150 days that each hedgehog was involved in the study was conducted that found there was no significant difference between wild and rehabilitated hedgehog survival (log rank test: chi-squared = 0.4, d.f. = 1, p = 0.542) (Fig. 3). Due to a lack of significance in survival between the first 150 days after release between wild and rehabilitated hedgehogs, the survival data across both treatments was pooled to enable a comparison between seasons. There was a significant difference in hedgehog overwinter survival rate by season, with survival rates being lowest in spring, compared to autumn and winter (log-rank test: chi-squared = 18.5, d.f. = 2, p < 0.0001) (Fig. 4).
Gender and age differences in over winter behaviour of wild hedgehogs
There were no significant differences (p > 0.05) in any of the variables (‘start weight’; ‘last weight’; ‘weight change’; ‘daily weight change’; ‘percentage weight change’ ‘nesting rate’; and ‘number of days tracked’) between wild male (n = 10) and female (n = 13) hedgehogs (Table 2). Adult wild hedgehogs (n = 17) were significantly heavier than young of the year (n = 6) at the start and end of the study, respectively (Table 2). However, there was no significant difference between adults and young of the year regarding weight change over winter, daily weight change or in the number of nests used per 100 days (Table 2). Therefore, hedgehogs of all ages and genders were pooled for comparisons in over winter behaviour between wild and rehabilitated conspecifics.
Comparison of wild and rehabilitated hedgehogs over winter behaviour and weight change
The average weight of rehabilitated hedgehogs upon release was 631.74 g ± 13.57 with a range between 391 g and 851 g. The average weight loss for hedgehogs over winter was 110.32 g ± 22.08 which equated to an average loss rate of 0.72 g/day ±0.19 (n = 39). There was no significant difference in weight loss or daily weight loss between wild and rehabilitated hedgehogs over winter (wild weight loss = −124.74 g ± 26.82 (n = 19), rehabilitated weight loss = −96.61 g ± 35.12 (n = 20), Mann-Whitney U test: W = 180 p = 0.792; wild daily weight loss = −0.79 g/day ± 0.17, rehabilitated daily weight loss = −0.65 g/day ± 0.35, Mann-Whitney U test: W = 211, p = 0.569). Average percentage of body weight loss across all hedgehogs over winter was 14.11% ± 3.08, with maximum percentage weight loss being 44.01%. There was no significant difference in percentage weight loss between wild (13.35% ± 2.88 (n = 19)) and rehabilitated (14.84 ± 5.44 (n = 20)) hedgehogs during the study (Mann-Whitney U test: W = 227, p = 0.309).
In total, 92 winter nests were utilised by 40 hedgehogs, with between 1 and 7 nests used per hedgehog. An average of 1.74 ± 0.20 nests was used every 100 days by hedgehogs over the study period. There was no significant difference in the rate of nest use between wild (n = 23; mean = 1.98 ± 0.32) or rehabilitated hedgehogs (n = 17; mean = 1.42 ± 0.2) (Mann-Whitney U test: W = 229.5, p = 0.359). The distance between successive nest sites ranged from 2 to 323 m for wild hedgehogs, and 6–245 m for rehabilitated hedgehogs. There was no difference in the mean distance between successive nests per hedgehog between wild (n = 17, 106 ± 16 m) and rehabilitated hedgehogs (n = 7, 82 ± 41 m) (t test: t = −0.55, df = 8, p = 0.598).