Acoustic analysis shows Clark’s Nutcracker seasonal and spatial habitat use during post-fire recovery of two endangered pine species

Whitebark pine ( Pinus albicaulis ) and limber pine ( Pinus flexilis ) are endangered species in Alberta that rely on seed caching by Clark’s Nutcracker ( Nucifraga columbiana ) for regeneration. Our objective was to determine which factors affect Clark’s Nutcracker habitat use at the northern range limit of 5-needle pine co-occurrence, during fall foraging when seeds are cached, and during the following spring when seed caches are retrieved. This information is essential to inform recovery plans on potential for natural dispersal and regeneration on burns intended for 5-needle pine management. On a large, 2009 prescribed burn in Alberta (5600 ha), we used six automated acoustic recording devices from fall 2018 to spring 2020 to quantify Clark’s Nutcracker habitat use. We tested whether Clark’s Nutcracker habitat use differed between mast (2018) and non-mast years (2019), between whitebark and limber pine habitat, and burned versus unburned habitat. We used KALEIDOSCOPE PRO acoustic analysis software to quantify nutcracker calls from nearly 2000 hours of recordings with an advanced classifier. Model selection using Akaike’s information criterion suggests that nutcracker habitat use depended on masting, habitat type, burned habitat, distance from seed sources, and one or more interactions, in both fall and spring foraging periods. Results from our study show that in the fall when both pine species produce high numbers of cones in close proximity, Clark’s Nutcracker used whitebark pine habitat more, particularly unburned stands, suggesting more caching behavior. In the spring when seeds are retrieved, nutcracker habitat use was greater in the non-mast year, particularly in burned whitebark pine habitat. These habitat-use results suggest that in the 2018 mast year, both pine species benefitted from attracting seed dispersers, and further benefitted from lower habitat use the following spring, when caches are vulnerable to seed predation by nutcrackers. Whitebark pine attracted more nutcracker habitat use with fewer trees, and fewer cones per tree than limber pine. The 2009 prescribed burn created attractive habitat for Clark’s nutcracker 9–11 years post-fire, demonstrating that opportunities for seed dispersal occur during this period. Continued use of trees resistant to white pine blister rust ( Cronartium ribicola ) by dispersers is essential for natural regeneration to be effective in current recovery strategies, and to leverage existing plantings of white pine blister rust resistant seedling as they reach cone production age in the future.