Large scale variation in birth timing and synchrony of a large herbivore along the latitudinal and altitudinal gradients

1. Hopkins’ Bioclimatic Law predicts geographic patterns in phenological timing by establishing a correspondence between latitudinal and altitudinal gradients. First proposed for key phenological events of plants, such as leaf sprouting or flowering dates, this law has rarely been used to assess the geographical equivalence of key life history traits of mammals.

2. We hypothesize that (H1) parturition dates of European roe deer (Capreolus capreolus) are delayed and more synchronized at higher latitudes and altitudes, (H2) parturition timing varies along latitudinal and altitudinal gradients in a way that matches the Hopkins’ Bioclimatic Law, and (H3) females adjust parturition timing to match the period of high energy demand with peak resource availability.

3. We used parturition dates of 7,444 European roe deer from Switzerland to assess altitudinal variation in birth timing and synchrony from 288 to 2,366 m a.s.l. We then performed a literature survey to compare altitudinal resu...