Histogram case study: variation in molting strategy of flight feathers and body feathers in North American Anseriformes
Hi all! I’m in Maryland right now and when I walk along the Chesapeake Bay, I notice that the Mallard ducks seem to be going into eclipse plumage. Information online on exactly when this eclipse plumage happens wasn’t super specific, so I used the histogram method outlined in my previous post to see when Found Feathers observations of waterfowl feathers had been made in the North American region.
This first graph made some sense, but I was thinking that there might have been a peak in July and not June since I’ve only just started seeing body feathers personally. So I filtered for "Feather Placement: Body” and lo and behold:
A late-summer peak beginning in July! And a second (or first?) peak in late winter/early spring, perhaps in preparation for the breeding season.
This made me wonder about the flight feathers, since I have heard that waterfowl drop them all at once, and in fact the eclipse plumage happens as a defensive measure during this time of vulnerability. So I filtered for primary and secondary wing feathers, respectively:
So these seem to peak in June, right before the body feathers are shed. Also note that they really do get dropped in a very narrow, very similar time frame. Interesting to see that in the same bird, there are different strategies for molting different kinds of feathers.
Side note: you can go a little more granular and look at week-of-year histograms, which reveal some differences between the primary/secondary molt timing not seen in the month-of year graphs (see below). However, with the very small n-count I think that the month-of-year view is probably more appropriate/useful.
What this view does tell you, though, is that you need to be out on the 24th week of the year to see the most waterfowl feathers in North America!
That was the week of June 12. Darn! I’ll have to plan ahead for next year :)
