Carnivore restoration has gained worldwide attention for bolstering not only recovering endangered species, but restoring ecosystem-level processes such as predation to potentially recover ecosystem function. Reintroduction of gray wolves (Canis lupus) to Yellowstone National Park (YNP) has been amongst the more successful and innovative ‘natural’ experiments. Juvenile recruitment of pups is perhaps the key demographic rate driving wolf population dynamics, yet is rarely directly studied, or based on minimum pup counts that assume 100% detection. We know social factors such as group size and composition affect adult wolf survival, yet there are few studies on their effects on pup survival. Wolf packs are highly visible in many areas of YNP, yet estimating detection and survival for juvenile wolves remains challenging due to imperfect detection of pups due to accessibility, visibility, and landscape conditions. Our goal was to harness a large dataset to estimate the effects of imperfect pup detection in YNP, and to estimate pup survival and effects of social factors on survival. We used 7,879 observations of pups from 4-5 wolf packs/year across a 22-year period (1996-2017) to estimate annual pup survival in YNP. Observations occurred between den emergence in early May and December to minimize misidentification of juveniles.
Results/Conclusions
Annual observations of juveniles ranged from 85 to 703, and averaged 358.1 per year. We surveyed an average of 4.57 packs per year and integrated this data into a hierarchical Bayesian N-mixture modeling framework that accounted for between-pack heterogeneity in detection rates, temporal variation, and social factors. Our results indicate detection was indeed << 1.0, p=0.23/sighting, and very heterogenous between packs. Failing to account for imperfect detection significantly biased juvenile survival rates. Our hierarchical model indicated that juvenile survival from den emergence in early May to December 31 to be ~ 0.50 across years and packs. Detection is an important factor to consider when estimating juvenile survival, and raw pup counts should be discounted. Preliminary results show that pup survival was positively associated with both larger pack sizes, and, more diverse age-structure amongst the pack that supported indirect effects of sociality on demography in this highly social species.