Migratory Songbirds as Potential Ectozoochorous Protist Dispersal Vectors

Protist biogeography, speciation, and systematics continue to generate debate and inquiry because protist distributions and dispersal remain poorly resolved. Identifying potential vectors and basibionts for epibiont protists would contribute to our limited understanding of their ecology. Migratory animals seasonally link disparate landscapes, incidentally transporting other organisms in the process. Waterbirds are known microbe dispersers, but evidence for other avian groups is limited-such as taxa that often migrate longer distances. We asked whether terrestrial songbirds (Passeriformes) host diatoms (Bacillariophyta) by sampling tail plumage of four thrush species (Hermit Thrush Catharus guttatus, Swainson's Thrush C. ustulatus, Wood Thrush Hylocichla mustelina, American Robin Turdus migratorius) spanning multiple migration strategies. Unexpectedly, we found diatoms in all seven samples (n = 4 tail snips, n = 3 tail swabs), yielding 224 individuals of 25 genera and 9 orders: primarily benthic, freshwater, raphe-bearing genera (e.g., Encyonopsis, Navicula, Nitzschia). Several diatoms contained chloroplasts prior to digestion and slide mounting, consistent with potential viability. These natural history observations suggest that songbirds are overlooked carriers of hitchhiking diatoms, implying an undescribed but potentially important avian-algal relationship.