Eyeing the camera, originally uploaded by Gavatron.
Griff, on the cusp between 11 and 12 weeks.
Content © Gavan P.L. Watson, Some Rights Reserved.
Archive: February, 2009
February 12, 2009
Double-crested Cormorants self medicate by swallowing stones
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.
February 8, 2009
Spring feels around the corner: things are moulting away…
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
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.
February 6, 2009
Knowing me, knowing you
If you’ve ever spent time watching House Sparrows (Passer domesticus), you might have noticed just how, well, squabbly they can be. Just today, I was out walking the dog, and a group of three came screaming (in flight and in sound) out from a pruned cedar shrub, flew across the sidewalk and screamed back into another shrub. They’re social little birds and use that sociality to their advantage–often relying on others to find food to eat. Fights between birds erupt over a number of different reasons (just like us, really) and food is often a source of conflict.
A recently-published paper in the journal Animal Behaviour1 reports the results of a study that looked at the effect of how being related to another House Sparrow might effect reactions over food.
The study suggests that the more closely related an individual House Sparrow was to another, the less likely there would be conflict (called “Aggressive Joining”) over food. If there was conflict with a close relative over food, less food would be taken from that relative.
Interestingly, there was a sex difference reported that was possibly attributed to the fact that female House Sparrows spread out over a greater distance from their original flock. If a male was to take food without conflict from another bird, it was always from a non-relative bird. Females, however, showed no discrimination when they were taking food (without conflict) from others. Since it is females that spread out, they’re less likely to have close relatives in their new flocks–hence they show no preference for taking food from close relatives or non-relatives.
Perhaps most interestingly, but not surprising, was the acknowledgement that House Sparrow have to be able to recognize and know close relatives:
Since we found differences between several aspects of scrounging behaviour towards close kin and nonkin birds, sparrows are likely to be able to distinguish between genetically closely related and unrelated flockmates.
Since House Sparrows neither breed co-operatively or form family groups, their ability to recognize close relatives is seen as significant.
So, now, while you’re sitting on a patio this summer and see House Sparrows at your feet, spend some time watching them and their reactions over food. You might be able to decide if they’re close relatives or simply strangers.
- Source Details: Zoltán Tótha, Veronika Bókonya, Ádám Z. Lendvaib, Krisztián Szabóc, Zsolt Pénzesc,and András Liker (2009). Effects of relatedness on social-foraging tactic use in house sparrows. Animal Behaviour, 77(2), 337. [↩]
Last sighting
