Dispersal plays a fundamental role in shaping communities. Bryophyte dispersal via air is often highly localized, and dispersal limitation has been demonstrated. Plants can greatly benefit from directed dispersal facilitated by an animal vector, but this process has been given little attention in bryophytes. Studies of animal dispersal of bryophytes are few, and have focused on dispersal of asexual propagules. Long distance dispersal by passerine birds has been speculated, but has not been explicitly addressed. Given the close association of birds with mosses during nesting and foraging, birds may frequently come into contact with bryophyte spores, many of which may adhere to the surface of bird feet and feathers.
We hypothesized that bird surfaces would regularly harbor bryophyte spores, and that spore load would differ with bird size, species, and foraging behavior. In order to address these hypotheses, passerine birds were captured via mist nets in the Wind River Experimental Forest in Gifford Pinchot National Forest, WA. Birds were topically sampled the legs, feet, and rectrices using cotton swabs. The number of spores from each sample were determined via microscopy and the abundance and comparisons between behavioral groups and species made.
Results/Conclusions
In total, 1,512 bryophyte spores were recovered from 224 captured birds, representing 27 different passerine species. Tarsal length was found to positively correlated with spore number (p<0.01) Foraging strategy differences in spore load were observed, with bark foragers (p=0.01) and foliage gleaners (p=0.04) carrying more spores than ground and aerial foragers. Birds species groups differed in their propensity to carry spores, with total spore load being higher in chickadees (p=0.01) and lower in hummingbirds (p<0.01) than other species groups. Thrushes carried significantly more spores on their tail feathers than other species (p=0.02).
We provide the first evidence of avian-mediated dispersal of bryophytes by passerines. Given the influential role of birds on the dispersal of tracheophytes, this newly described relationship has the potential to fundamentally improve our understanding of how bryophyte communities are formed and maintained. Avian behavior may impact the ecological community composition of bryoflora at both local and regional scales. By understanding this relationship we may enhance our ability to better project the development of epiphytic community recolonization in managed forested landscapes, as well as provide an independent system in which we can test dispersal theories developed in seed plant communities.