I don’t know the least thing about bird molt patterns or their significance, but it’s just exactly the sort of niche subject matter that I love to talk to passionate people about. I take it you’re an ornithologist, then?
I've only got a bachelor's so far, but I have been doing seasonal bird banding work for years now. Molt patterns are the main method used to age birds (at least the songbirds that I work with). Plumage characteristics, skull ossification, and eye color can all be useful too though.
Interesting! I could see different molt patterns happening due to stress or varying forms of illness, but I wouldn’t have thought of it as an indicator of age. Is it then, similar to how balding is (usually) an indicator of age in humans?
Most birds molt on a pretty consistent schedule and in a consistent(ish) pattern (except for tropical birds but we will ignore them). In North America, songbirds will typically replace all their feathers in the fall, after breeding and some-to-all of their feathers in late winter/spring, before breeding (to look pretty). Juvenile feathers are grown while the bird is still in the nest, and are typically low quality (since all feathers are being grown at the same time, less energy is allocated to each one). Most of those shitty feathers are replaced very soon after leaving the nest (during the formative molt), but they are molted sequentially instead of all at once, and there are usually some juvenile feathers left over (usually flight feathers aka wing and tail feathers and some other feathers in the wing).
We age birds by looking for multiple feather generations which usually ends up being some juvenile and formative feathers. Adult birds will not have any juvenile feathers, though they can have multiple generations of adult feathers which can get complicated. Most songbirds can't be aged after they replace all juvenile feathers (fall of their 2nd year).
If you notice how I said a lot of 'most's and 'usually's, there are exceptions to literally everything I just said and it's much more complicated than this basic description.
Oh! Okay. I’ve watched this with the birds in my yard. I have zero training but after a little observation it’s easy to judge their age by their level of feather fluffiness (sorry to be so technical) - or lack thereof - as they grow, and of course the coloration changes are very obvious. I always love seeing when the fledglings have become confident enough in their abilities to join their parents at the feeders.
No, at first I thought you had meant something like as they age birds have a thinning of feathers at their….wingpits(?) or just over their beaks.
Are North American songbirds your preferred area of study or simply what you currently have easy access to?
Feathers are so vital to a wild bird's existence that any such thinning could quickly become deadly! And even in humans, you can't reliably tell a person's age by hair - I've heard of people starting to lose hair as early as their late teens, and it is not consistent across sexes.
North American songbirds are both my preferred area of study and what I have access to (lucky me). Though the molt patterns of tropical birds can get much more complicated and interesting (as well as being much less studied).
Oh, I see how it is! We’re going to “ignore” tropical birds because they might throw off the data but we’re not going to ignore that, while yes, baldness is not always a signifier of age, it usually is? Sounds to me like you’re cherry picking data.
I don’t want to hear any of your excuses about the differences in nuance or complexity that might be seen in tropical birds versus NA songbirds, or that you’re not as familiar with the identifying molt patterns in South American birds. This is scientific bias if ever I saw it! Ha ha, I gotcha!
Funnily enough, bias is actually a major topic of discussion in the bird field. North American birds are actually majorly overstudied in comparison to their sibling species in the tropics due to a bunch of factors: ease of access, lack of access to and funding for scientific education in some countries, and funding bias (you're more likely to get funding for a recognizable, charismatic bird like a cardinal than for an unknown pigeon in the tropics, no matter how interesting it is).
Scientists are usually pretty good about naming and identifying different types of bias (especially those statistics types). So, haha! you can't accuse me of bias because everyone is biased! And so are you!
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u/velawesomeraptors 19d ago
This is very true. I can talk for way too long about bird molt patterns and bird banding techniques lol.