Effects of willow nutrition and morphology on calving success of moose

Abstract

Across much of North America, populations of moose (Alces alces) are declining because of disease, predation, climate change, and anthropogenic‐driven habitat loss. Contrary to this trend, populations of moose in Colorado, USA, have continued to grow. Studying successful (i.e., persistent or growing) populations of moose can facilitate continued conservation by identifying habitat features critical to persistence of moose. We hypothesized that moose using habitat with higher quality willow (Salix spp.) would have a higher probability of having a calf‐at‐heel (i.e., calving success). We evaluated moose calving success using repeated ground observations of collared individuals with calves in an occupancy model framework to account for detection probability. We then evaluated the impact of willow habitat quality and nutrition on moose calving success by studying 2 spatially segregated populations of moose in Colorado. Last, we evaluated correlations between willow characteristics (browse intensity, height, cover, leaf length, and species) and willow nutrition (dry matter digestibility [DMD]) to assess the utility of using those characteristics to assess willow nutrition. We found willow height and cover had a high probability of being positively associated with higher individual‐level calving success. Willow DMD, browse intensity, and leaf length were not predictive of individual moose calving success; however, the site with higher mean DMD consistently had higher mean estimates of calving success for the same year. Our results suggest surveying DMD is likely not a useful metric for assessing differences in calving success of individual moose but may be of use at population levels. Further, the assessment of willow morphology and density may be used to identify areas that support higher levels of moose calving success.

Efficacy of Killing Large Carnivores to Enhance Moose Harvests: New Insights from a Long-Term View

“…Nevertheless, forage-based methods, including those implemented in Alaska [18,[54][55][56][57] for estimating K (or some reproductive variables related to K) are available, but these are labor intensive; forage measurements also may lag declines of ungulate populations [5]. Moreover, browsing intensity by moose was not predictive of calving success [58]. and measures of willow quality can vary markedly in response to annual patterns of weather [10].…”

“…Moose would be expected to respond reproductively to such variation in forage quality only when populations were near K, and forage was limited. In addition, the relationship between ungulate density and forage productivity may not be linear, especially at low densities of ungulates [58,59], which reduces the reliability of measuring forage to understand population dynamics of moose. Further, moose sexually segregate in spring and winter [60][61][62], necessitating that ranges used primarily by females be sampled to assess population productivity, a critical factor that often is ignored [63].…”