Sequential twig selection and biomass consumption of willows by moose calves in winter: a test of optimal patch use theory

A better understanding of how moose Alces alces select and browse plants may allow ecologists to make better predictions about how herbivores and plants interact, herbivore food acquisition, and how organisms may shape their own forage supply. This in turn, can lead to a better understanding of animal responses to plant nutrients and defences, and how and why animals move across landscapes, select certain habitats, reproduce, interact with predators and competitors, and survive. Here, we used sequential feeding trials conducted in north-central British Columbia with 4 hand-reared, 9-month-old, orphaned moose calves to study winter shoot selection from ramets cut from native willows Salix scouleriana. Our generalized linear models indicated that, when browsing, moose calves generally followed principles of optimal patch use theory and initially selected smaller, less fibrous shoots at the beginning of feeding trials, then switched to larger shoots as smaller, more nutritious shoots were depleted. On average, moose calves removed 20% of the shoot biomass from each ramet trialled and cropped shoots at an average of 5.03mm in diameter. Bite diameters taken by calves were larger when a greater proportion of shoots from ramets had been selected from ramets that had been browsed in previous years and in later feeding trials. Despite some study limitations, our findings provide these and other fine-scaled details contextualized within a backdrop of prior research regarding browse selection by young moose that may help to elucidate connections between browsing behaviours and estimates of intake rate. These findings may help to inform future studies in which forage ecologists are seeking to understand optimal foraging and browse patch depletion dynamics in moose and other species.

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