Implications of the forage maturation hypothesis for activity of partially migratory male and female deer

Abstract

Citation: Debeffe, L., I. M. Rivrud, Ø. Brekkum, E. L. Meisingset, and A. Mysterud. 2017. Implications of the forage maturation hypothesis for activity of partially migratory male and female deer. Ecosphere 8(12):e02050. 10. 1002/ecs2.2050 Abstract. Partial migration is common in a large variety of taxa in seasonally variable environments.Understanding the mechanisms underlying migration is important, as migration affects individual fitness. Migratory herbivores benefit from delayed forage maturation and hence higher food quality during migration and at their summer range, termed the forage maturation hypothesis (FMH). The link between diet quality and rumination time allows migrants eating a higher quality diet to spend less time on rumination, and they can thus allocate more time to additional feeding. However, such an argument implicitly assumes that deer are energy maximizers, while studies have reported also time minimization strategies under risk of predation. Male and female distributions are limited by different factors linked to both body size differences and reproductive strategies, but there is no study investigating differences in activity pattern according to the individual migratory patterns for male and female deer. We here unify the FMH with the hypotheses predicting sex-specific time allocation strategies. To test predictions of sex-specific activity of resident and migratory red deer (Cervus elaphus), we analyzed activity data of 286 individuals that were fitted with GPS collars from a population in western Norway. While migrants were more active during the migration itself, we found no differences in activity pattern between migrant and resident deer during the main growth season, neither in terms of proportion of daily time active nor in terms of daily mean movement speed, thus rejecting that deer were energy maximizers. Overall, we found that females were more active during the main growth season even after controlling for body size differences. These patterns are consistent with patterns predicted from sexual segregation theory linked to the reproductive strategy hypothesis. Our study highlights how the understanding of migration can be advanced by considering it in the context of different reproductive strategies of males and females.

Sex-specific differences in spring and autumn migration in a northern large herbivore

“…In contrast, females migrated at higher speed, especially during spring and when leaving their seasonal range early, possibly to reach their summer range before upcoming parturition. At the daily scale, females were more active than males during both spring and autumn migrations, which is consistent with the higher female activity previously reported during the main growth season 25 . The use of stopover sites also differed between sexes, with a decreasing probability of using stopovers with later departure timing in males, while a weaker effect was found in female with the reverse trend, also suggesting different constraints and responses.…”

“…Sixty-two percent of the collars included a dual-axis acceleration sensor that counts both horizontal and vertical individual neck movements, allowing to discriminate active (i.e., all behaviour confounded) and inactive time. The proportion of daily time active was calculated as the number of activity values set as active (ie., above a threshold value) during a day divided by the total number of values obtained on that day 25 . Days with less than five activity values were discarded.…”

“…In addition, the rutting season overlaps with the autumn migration season in many species, and onset of male migration in autumn is less linked to environmental stimuli compared to female autumn migration in red deer ( Cervus elaphus ) 24 . However, migration is rarely framed highlighting the different seasonal limitations on fitness of male compared to female ungulates 25 , and we lack an understanding of how different processes affect migration characteristics in spring versus autumn comparatively in male and female ungulates. In polygynous mammals, different factors limit male and female fitness 26,27 .…”

Fallow deer foraging alone does not preserve the vegetation of traditionally sheep‐grazed calcareous grasslands

“…Our findings are in line with the forage maturation hypothesis, which could often be supported in studies on cervids (Debeffe et al, 2017; Riesch et al, 2019). This hypothesis states that deer strongly prefer early phenological stages for foraging because of better digestibility and higher nutritious value.…”

Grazing by wild red deer: Management options for the conservation of semi‐natural open habitats

“…This temporal association was corroborated by significant positive linear relationships between daily forage removal in grasslands and productivity and CP, respectively (Tables S6 and S7). The forage maturation hypothesis, widely supported in cervids (Debeffe, Rivrud, Brekkum, Meisingset, & Mysterud, 2017;Fryxell, 1991;Mysterud, Vike, Meisingset, & Rivrud, 2017), can explain this seasonal pattern: red deer strongly select for vegetation in an early phenological stage because it offers easily digestible and highly nutritious forage. From a conservation point of view, high forage removal in grasslands during spring and early summer is essential to prevent the accumulation of unpalatable dead plant material (Crofts & Jefferson, 1999) that grazing animals would reject in the later season and that could introduce changes in the plant community conflicting with conservation aims.…”