Abstract
Typically, large ungulates show a single seasonal peak of heart rate, a proxy of energy expenditure, in early summer. Different to other large ungulates, wild boar females had peak heart rates early in the year (at ~ April, 1), which likely indicates high costs of reproduction. This peak was followed by a trough over summer and a secondary summit in autumn/early winter, which coincided with the mast seeding of oak trees and the mating season. Wild boars counteracted the effects of cold temperatures by decreasing subcutaneous body temperature by peripheral vasoconstriction. They also passively gained solar radiation energy by basking in the sun. However, the shape of the seasonal rhythm in HR indicates that it was apparently not primarily caused by thermoregulatory costs but by the costs of reproduction. Wild boar farrow early in the year, visible in high HRs and sudden changes in intraperitoneal body temperature of females. Arguably, a prerequisite for this early reproduction as well as for high energy metabolism over winter is the broad variety of food consumed by this species, i.e., the omnivorous lifestyle. Extremely warm and dry summers, as experienced during the study years (2017, 2018), may increasingly become a bottleneck for food intake of wild boar.
Highlights
Large ungulates show a single seasonal peak of heart rate, a proxy of energy expenditure, in early summer
Mean hourly heart rates (HR) was significantly affected by all variables investigated (Fig. 1, Table 1)
Female wild boars showed two peaks of HR, the highest peak around 1 April and a second peak around 1 December, while a trough occurred during the summer months, June–August (Fig. 1a)
Summary
Large ungulates show a single seasonal peak of heart rate, a proxy of energy expenditure, in early summer. Different to other large ungulates, wild boar females had peak heart rates early in the year (at ~ April, 1), which likely indicates high costs of reproduction. This peak was followed by a trough over summer and a secondary summit in autumn/early winter, which coincided with the mast seeding of oak trees and the mating season. “Climate plays an important part in determining the average numbers of a species, and periodical seasons of extreme cold or draught, I believe it to be the most effective of all checks”. While the seasonal reproductive cycle in these short-day breeders is principally governed by photoperiod and melatonin[12,18] environmental conditions such as climate and food supply have a modulating effect on wild boar reproduction
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