Eyeing the camera, originally uploaded by Gavatron.
Griff, on the cusp between 11 and 12 weeks.
Eyeing the camera, originally uploaded by Gavatron.
Griff, on the cusp between 11 and 12 weeks.
A just-published paper suggests that Double-crested Cormorants (Phalacrocorax auritus) in the Great Lakes may swallow stones to reduce the number of parasitic nematodes–and in so doing, are self-medicating. Many birds ingest stones to help with the digestion of physically hard objects, but fish, the primary meal of the DCC are soft-bodied and don’t need the kind of mechanical assistance. So why are DCCs found with ingested stones?
Researchers found that:
At a Lake Ontario site, females more often had small stones in their stomachs and were less parasitized by nematodes than were males, and males with small stones had fewer nematodes than males without small stones. We did not find similar patterns in small stone presence or parasitism at a Lake Erie site; however, Lake Erie birds had fewer parasites and lower proportions of birds with small stones.
Which, in turn lead to the conclusion that since the birds that had stones were less likely to have nematodes, then the stones are the bird-equivalent of some anti-worm medication. Smart birds.
Small rant:
Interestingly, the Lake Ontario site was located at Presqu’ile Provincial Park and the Lake Erie site was located at Middle Island, Ontario. These are two sites where DCC culls have taken place in the recent past, with websites reporting a May 2008 cull on Middle Island that matches with the date in the paper’s method section. I can’t find any mention in the paper to the “source” of the birds or how the birds were “collected”.
Some may say there is no space for politics in scientific research and regardless about your feelings about recent DCC culls, I think that because the article makes no specific mention of how and where the researchers got their DCC gastrointestinal tracts, it does nothing but reduce the transparancy and therefore, the quality of the work.
The past two days in Toronto have been warmer than normal, leading to a large snow melt and the promise of spring (and I know it’s a tease, but it’s a nice break from what has felt like an especially cold winter). With spring comes the return of migratory birds, so this research seems relevant.
First, some background. Feathers, unlike our bones, lack an ability for self-repair. They can be attacked by feather-loving bacteria1 and suffer from UVB damage (and sunblock doesn’t really help out). So birds moult, or replace feathers, up to twice a year. According to my Sibley Guide to Bird Life and Behaviour, most North American birds replace feathers in a complete moult in the late summer or early fall. Some birds undergo a second moult in the spring, before the breeding season.
Birders out there have experienced these two moults when faced with confusing fall warblers: males no longer are in their colourful, easy-to-identify plumage (which appeared during the spring moult) and we humans suffer under the burden of having to learn, what could easily be described in some cases, as a whole new bird.
Why there is a difference in moults is the subject of this research by Thomas P. Weber, Johan Borgudd, Anders Hedenstram, Kent Persson & Garan Sandberg. Comparing the mechanical strength of flight feathers from two species of similar birds that have different moulting strategies, researchers found that the bird species that moults twice2 have comparatively weaker (more prone to fatigue) feathers than the species that moults once. Since the authors suggest that “the species with feathers that fatigue faster moults twice annually and not once” it would seem the willow warblers moult out of a form of necessity: they would suffer from the consequences of weakened feathers as they migrated to or from their breeding territory.
Now, if this feather weakness is a similar case for birds of the Americas that moult twice, it’s interesting to note that Wood Warblers (Family Parulidae) also change the colour of their plumage with the two moults. Because of this breeding plumage / winter plumage dichotomy, it would seem that feather weakness isn’t the only reason why a bird would moult twice. The interesting question would be if the adaptation to two moults a year “allowed” wood warblers to have a colourful breeding plumage–the ability for males to “change” their appearance for the breeding season and visually demonstrate just how fit they are.