Local mortality events in migrating sandpipers (Calidris) at a staging site in southern Brazil

In this paper we report two mortality events affecting three sandpiper species, Red Knot Calidris canutus, White-rumped Sandpiper C. fuscicollis and Sanderling C. alba, during northward migration through southern Brazil. Relative to local abundances of the three species studied, Red Knots were by far the most affected, with first year males and lighter birds suffering the highest proportion of mortality. A total of 54 birds (40 Red Knots, 11 White-rumped Sandpipers and three Sanderlings) were recovered for toxicological, parasitological and bacteriological tests. Tests for Pasteurella sp. and algal toxins were mostly negative, although the effects of other toxins, including domoic poisoning, could not be ruled out. Dissections disclosed the presence of acanthocephalan Profilicollis sp. and trematode (Cyclocoelidae) parasites. Microbial evaluations resulted in the isolation of bacteria (genera: Aeromonas, Pseudomonas, Shewanella,  Enterococcus, Escherichia, Proteus, Citrobacter) in a subset of the dead birds, with highest prevalence in knots. These parasites and infections may have increased susceptibility to, or been exacerbated by, the fatal disease or poisoning, but were not likely the cause of death. Although we were not able to determine the definitive cause of death, studying these local mortalities allowed us to report the presence of helminths and bacteria carried by shorebirds and to  investigate several possible causes of mortality.