Anyone who’s visited Great Island and Jeremy Point will appreciate the difficulty of accessing the area, and the challenges of the terrain. Add in the exertion of hacking off wings with pruning shears, and you get a recipe for a rugged day in the field. The wings harvested will substantially boost the efforts to track these eiders back to their land of origin.
A few blog readers have raised good questions about the die-off investigation, and I wish to address these here. The first: why does it seem to be almost exclusively male eiders involved? Is it just that they are more noticeable with their black and white plumage? While the striking colors do tend to make the males more eye-catching, in fact, the die-off population shifts over the course of the Fall. In late August and September, we see a spike in mortality in females. By October, the males become more prominent. The reason may lie in the migratory ecology of the species. After breeding in the Spring, the males and females go their separate ways. Multiple females raise their collective young in groups calls creches, while males head off into the wilderness. Females and males both molt prior to their Fall migration, but the timing can be staggered, and they molt in different geographic locations. Given that, it’s no surprise that males and females turn up separately on Cape Cod beaches. Another question arose in light of attempts to determine the source of the Wellfleet Bay Virus (WFBV) which has killed at least some of the birds. Scientists investigating the virus have postulated that ticks may be involved in the virus’ spread. But how, asked some of you, would ocean based ducks get infested with ticks? Well, even a sea duck comes ashore to lay eggs (the females, anyway), and research across seabird groups has shown that ticks are common on breeding islands, some specific to a particular host species, and others able to feed on multiple bird species. Some of the ticks will feed on a nesting host, then drop off onto the ground and survive through an entire year without feeding until the birds return to breed again the next season. And viruses have been shown to be viable within ticks for two full years. Whether the females might contract the disease from ticks, and then pass the ticks themselves to males during breeding, or whether the virus is spread from bird to bird in some alternate manner is entirely unknown now, but is most certainly an area of active research. As dead eider season winds to a close, we recognize the hard work of everyone involved in this investigation, but cannot resist a particular SEANET shout-out to Dick, undaunted out there on MA_21. Thank you, Dick; you’re awesome!