Results
Between 2010 and 2019 a total of 9,981 mountain hare observations were obtained at 678 camera trap locations (Figure 1 and Suppl 4). Only two observations were recorded in 2010, which we discarded due to the small sample size. Of the remaining observations, 7,454 were recorded in “spring” and 2,525 were recorded in “autumn”. The number of camera traps deployed across Norway increased throughout the study period, leading to an increase in the number of observations obtained in each year (see Suppl 3 for location of traps that recorded observations in each year). Camera traps that recorded mountain hare observations were located between altitudes of 0 and 841 m.a.s.l., latitudes were between 58° N and 69° N, and climate zone PCA values were between -2.68 (coastal climate) and 2.86 (continental climate).
The results from our multinomial logistic regression model indicate that all three explanatory covariates, altitude, latitude, and climate zone, correlated with moult timing in spring and autumn. We found strong evidence for hares keeping their winter white coats for a longer duration at increased altitude and latitude (Figures 2.a and b.). The probability of being white increased with altitude in spring (β2,white = 1.492, 95% credible interval (CI) = 1.309 to 1.673; Figure 2.a) and in autumn (β2,white = 0.870, 95% CI = 0.639 to 1.117; Figure 2.a). Similarly, the probability of being white increased with latitude in spring (β3,white = 2.472, 95% CI = 2.265 to 2.672; Figure 2.b) and in autumn (β3,white = 0.642, 95% CI = 0.443 to 0.844; Figure 2.b). Climate zone had the smallest effect size in both spring and autumn. The probability of being white decreased with an increasingly inland climate (increasing PCS values) in both spring (β4,white = - 0.335, 95% CI -0.510 to - 0.163; Figure 2.c) and autumn (β4,white = - 0.287, 95% CI - 0.525 to - 0.053; Figure 2.c).
The ordinal day where the probability of being white is 50 % occurred 27 days earlier in spring and 23 days later in autumn for hares at sea level compared to 700 m a.s.l. (Figure 2 a). At 59° N the ordinal day where the probability of being white is 50% occurred 27 days earlier in spring and from brown to white 14 days later in autumn compared to hares at 65° N (Figure 2.b). Hares living in inland climates moulted 9 days earlier in spring and 11 days later in autumn (Figure 2. c).
Mountain hare moult timing varied across mainland Norway (Figure 3). Starting in mid-winter moving into spring, there was a travelling wave of moulting moving from lower to higher altitudes and latitudes (Suppl 10). The opposite effect was observed in autumn. The altitudinal and latitudinal moult timing gradients show that hares that inhabit mountainous areas and the north of Norway kept their winter white coats for longer than their conspecifics that inhabit low altitude and latitude areas. The model output, which represents all of Norway, indicates that mountain hares in coastal areas moult later in spring and earlier in autumn (Figure 2.c.). The prediction maps show that hares in southern Norway’s coastal areas Norway moult earlier in spring and later in autumn (Figure 3.a and 3.f.), indicating that the effect of latitude is stronger than the effect of climate zone. This is consistent with the climate zone effect sizes being smaller than those of altitude and latitude. Predictions for areas outside of camera trap locations (Figure 1) should be interpreted with care as these results are extrapolated.