A great question was sent into the 10,000 Birds Clinic today that has triggered off a train of thoughts and that led inevitably to this post. The questioner, Kathy, sent in three photos of a rather scruffy bird she’d found by her Toronto home which she thought she could identify but wasn’t 100% sure. Somewhat like an American Robin but ‘lazy’ and spotty, what exactly is this unusual bird, she asked?

Juvenile American Robin. Photos copyright Kathy Bosquet.

Have a look at the photos above and that’s actually a pretty good description of a juvenile American Robin - which is the bird that Kathy was asking about. I’m sure there are going to be quite a few new or occasional birders wondering exactly the same thing at the moment - because as early summer progresses our gardens, yards, parks etc will (hopefully) increasingly be filled with this year’s avian teenagers, young birds old enough to have fledged (ie left the nest) and which are prepared to make a half-hearted effort to look after themselves, but are not yet old enough to have moulted into a more adult-like plumage and look after themselves properly. And - metaphorically - many of them don’t seem to take too much trouble getting dressed in the morning! (The tone of this post may seem a little age-ist, but I’m looking back at myself fondly rather than disparagingly around me I promise.)

Most juvenile birds have similarly “scruffy” appearances to this one - incidentally, technically a juvenile is any bird that is still in it’s first plumage (the one it leaves the nest in) and an immature is any bird that’s not yet an adult regardless of its plumage or age, so juveniles are immatures, but not necessarily vice-versa. This is because juvenile birds need to grow the feathers very quickly so that they can get away from the nest into the safety of thick cover as quickly as possible - nests may seem a cosy place to hang out, but to a predator a nest full of helpless birds is little more than an invite to a free dinner! The trade-off for this rapid growth is that a bird’s first feathers are not as strong or hard-wearing as the ones they’ll grow as they age, and they tend to be moulted and replaced after just a few months: hence juvenile birds often seem to look ‘fluffy’ or in a continual state of scruffiness.

But even if the feathers aren’t as strong why should young birds look so different from the adults they grow into? There are apparently a number of reasons why young birds in general have different plumages to adult birds. Obviously one is that a plumage made up of spots and broken patterns is harder to see in the shady undergrowth or tree canopy that many young birds hide away in than solid colours and bright patterns. In other words cryptic patterning helps to camouflage the young, often still flightless fledgling when it’s at its most vulnerable and can’t so easily escape predators by flying away (this is the time of year, of course, when urban cats can wreak such havoc on bird populations by picking on flightless juveniles so please keep an eye on your pets). Many female birds have similarly drab, muted plumages for more or less the same reason of course: it makes them far harder to see when they’re egg-laying and sitting on the nest, a time when they’re particularly vulnerable too.

Another reason is that a distinctively juvenile plumage clearly establishes the young bird as a non-adult and apparently stops them being attacked by adult males whose sex hormones are still raging and who might see there own offspring as potential rivals. Birders commonly throw their hands up in despair at the many plumages that, for example, gulls go through as they age but studies clearly show that in the charged atmosphere of a tightly-packed breeding colony youngsters need to look very different to their own parents to avoid being driven from the nest before they’re capable of surviving on their own. Knowing that, the next time you scratch your head over the identification of a young larid maybe you might have a little more sympathy eh?

Juvenile Black-headed Gull, Chew Valley Lake, June 2008.

Juvenile plumages are quickly replaced/partially replaced in many species, and within a short time (usually by the end of the summer) most birds become more recognisably adult-like. This is certainly the case with the American Robin which will much more closely resemble an adult female before it migrates south - have a look at the American Robin in the photo below, which was taken in Philadelphia in late-September. Whilst still slightly spotted on the mantle, most birders would be able to identify this bird without too much trouble (and without looking too closely might not realise that it wasn’t an adult at all)…

One very interesting aspect of an American Robin’s spotty juvenile plumage is that it is common to all thrushes and their allies in the huge family Turdidae. I’ve posted before about how American Robins are in fact thrushes very closely related to the European Blackbird or the Asian Dusky Thrush rather than to “robins” (The REAL red, red Robin) - but robins, robin-chats, wheatears, and flycatchers in the family Muscicapidae all have juvenile plumages that are spotted and essentially “thrush-like” too, indicating that - once upon a time - the two families most likely had common ancestors and are very closely related.

Juvenile Cape Robin-chat, June, and Adult, January, Nairobi, Kenya.

Taxonomists currently place Turdids and Muscicapids next to each other in the avian “family tree” and over the years groups of birds within each family have been moved to the other and back again: further studies (probably primarily genetic) will undoubtedly throw up other questions and answers relevant to family linkages - and (if we understand them) we here at 10,000 Birds will be here to write about them, so check back!