Preferences of avian seed-hoarders in advance of potential American chestnut reintroduction

Abstract

Nut-bearing trees such as oaks (Quercus genus) and American chestnut (Castanea dentata, hereafter: chestnut) rely on scatter-hoarding animals for seed dispersal. With the pursuit of blight-resistant chestnuts for eventual reintroduction into eastern hardwood forests of the United States, it becomes important to understand how foraging preferences of avian seed-hoarders will influence chestnut dispersal in oak-dominated forests. Using six seed selection trials over three years and two “seasons” (early fall and late fall), we assess the relative seed preferences – when gathering seeds for hoarding or consumption – of five species of avian seed dispersers in southeast Ohio. In each trial, we presented an equal number of chestnuts and two species of common acorns, black (Q. velutina) and white oak (Q. alba), to wild birds on feeding platforms monitored by cameras. We used Bayesian discrete choice models to determine preferences of each species, and estimate the influence of natural variation in background mast availability (i.e., different years and seasons). Blue Jays (Cyanocitta cristata) showed a consistent preference for the seeds of black oak over chestnut over white oak, and the strength of preference for black oak increased in late season when acorns were scarce. Other species showed variable preferences, with White-breasted Nuthatch (Sitta carolinensis) the only species to prefer chestnuts over both acorns, though sample size was small (n = 26 selections). Our results suggest chestnuts are used by a host of avian seed-hoarders that may facilitate dispersal of chestnut, particularly in years of black oak mast failure.