Feather wear and moult in Waders: part 3 - Juvenile to 1st winter

A long time ago now I did a couple of blogs on moult in waders. Part 1 dealt with the basics of wear and moult, and looked at this process in an adult Curlew Sandpiper.

Part 2 looked at juveniles. It included the comment: " By this time, the bird is ready to undergo its first moult - into '1st winter plumage'. But that will have to wait for another post!" Well, it's been a long wait, but I realize that I did do some more pictures showing the progression from juvenile to first winter plumage which I never published, so here they are - not the complete set...watch this space (but don't hold your breath!)











Animated version here.

Up to this point the bird is still in complete juvenile plumage; the differences in appearance can be explained by the gradual wearing away of pale feather edges, which makes the bird's overall appearance plainer and darker.















In this series of pictures, two processes are going on. Wear is still occurring to the old juvenile feathers, making them duller and the patterning on them less distinct. At the same time, these old feathers are gradually being moulted or replaced by new, fresh non-breeding plumage feathers. On Curlew Sandpiper, these are generally plain and grey.The head and body feathers (including the mantle, scapulars and underparts) are completely replaced, and a variable number of wing feathers are as well.

Some of the changes are rather subtle, and might be more easily seen in the animated version here.

By November, first-winter birds look very similar to adults in non-breeding plumage (I haven't completed the sequence yet!), but they can usually be aged by the presence of a few old juvenile feathers (coverts) which retain their distinctive pattern, albeit much faded. Even where juvenile feathers lack distinctive patterning, they can often be differentiated from adult non-breeding feathers by their more ragged, heavily worn appearance. Moult proceeds assymetrically, so it's always advisable to get a good look at both sides of a bird as often, the 'give-away' juvenile feather may only be present on one wing.

Feather wear and moult in Waders: Part 2: Juveniles

Generally, adult waders leave the breeding grounds earlier than juveniles, which presumably need to spend longer growing and developing peak condition for the southward migration.

This means, rather amazingly, that the juveniles have to navigate their way southwards without the benefit of guidance from birds that have travelled the route before.

In Malaysia, in my limited experience, the first juveniles turn up three weeks to a month after the first returning adults.

In a study I did 2 years ago, Lesser Sand Plovers were the first juveniles to arrive - around the end of August, followed by Greater Sand Plovers in the first week of September. These two species breed quite well south of the majority of northern breeders, a factor which may have something to do with their earlier arrival. Curlew Sandpiper, Ruddy Turnstone and Common Sandpiper juveniles arrived in the third week of September, and and juveniles of most other species by the last week of that month.

How does one go about telling juvenile waders from adults? It is easier with some species than others. Generally, the larger plovers, curlews and snipe are rather tricky, whereas smaller sandpipers, shanks, and godwits should be quite obvious given good views. For details on how to tell the difference between juveniles and adults, you need to get a decent field guide to birds of the region. I find Robson's Birds of South-east Asia one of the most accurate, though the large selection of birds illustrated can be confusing to the beginner.

In many species, juveniles have more highly-patterned upperpart feathers than adults. The scapulars are smaller than adults, which can make the wing coverts more visible.



Continuing with the theme of Curlew Sandpipers (see Part 1 here), fresh juveniles often have a gorgeous pale peach or buffish wash to their breast and upperpart feathers. Note also the distinctive dark 'arrowheads' on the larger upperpart feathers - the scapulars, tertials and greater coverts. These will become darker and more obvious as wear takes place. Juvenile Red-necked Stints have similarly-patterned scapulars (hint - scapular pattern is one of the key things to look for when trying to identify waders!)


The initial effects of wear can quickly make a big change to the appearance of juvenile Curlew Sandpipers. The peach-buff colour quickly wears away, making the bird look much more grey. The dark parts generally become darker and the pale areas lose their colour, becoming either grey or whitish.


As abrasion continues, pale feather fringes wear away, and the colour of the bird darkens, making it more nondescript. By this time, the bird is ready to undergo its first moult - into '1st winter plumage'. But that will have to wait for another post!

Click here for the animated version!




You can see a similar process at work with these juvenile Lesser Sand Plovers. Both pictures were taken at the same place on the same day, 8th Sept 2006 - see here for the proof! The lower bird is much more worn than the upper one, and in fact it may have started its moult into 1st winter plumage (the crown?).

This variability can be confusing, but understanding the process of feather wear and how it affects the bird's appearance is an important key to making sense of it all. For a helpful explanation of moult in waders (though with a British bias), see this article by Keith Vinicombe.

Feather wear and moult in Waders

It won't be long before we start seeing the first returning waders coming south from their breeding grounds in Northern Asia, so I've been putting together a few graphics to explain a bit about feather wear and moult, which can cause confusing variation to the budding wader watcher!


Feather Wear

Feathers are damaged by a variety of natural factors - water, wind, sunlight, time - to name a few. Waders, which live in the exposed environment of coastal mudflats and sandy shores, and undertake long-distance migrations, are particularly likely to experience feather damage.

Naturally-occurring damage to feathers is known as 'wear' or 'abrasion'.

Parts of the feather which have no pigmentation (white) or light colouring are weaker than parts with dark pigment, so they usually wear away first (you can see the same effect with old flags - the white parts disintegrate before the coloured parts).

The dark areas of the feather may initially grow darker as pale areas are lost, but eventually grow paler, as a result of bleaching.

As feather wear affects almost all exposed parts of the bird, it has a major effect on the appearance of a bird's plumage.

Here's a scapular from a juvenile Red-necked Stint. Click on the image to see how wear affects its appearance.



The white tip wears away first, followed by the pale feather edges. The feather shaft is much stronger than the 'vanes', so eventually protrudes from the rest of the feather like a spike.

Here's a Wood Sandpiper's tertial. Click on the image to see how wear affects its appearance.


In this case, the white areas are in 'notches' along the feather fringe. As they wear away, the feather becomes indented. A bird in fresh plumage will appear speckled, while a worn bird looks much plainer and darker.



Here are photographs of two Wood Sandpipers at the same location, taken just 9 days apart - on 20th August and 29th August 2007. The upper bird is in extremely worn breeding plumage, so looks quite brown and plain. The lower bird has mostly moulted into fresh non-breeding plumage, and so shows lots of whitish speckles on the plumage.

Moult

Because feathers naturally wear away with time, and also for other reasons, birds periodically replace their feathers. This process goes on throughout the year, but is primarily concentrated in two seasons - pre-breeding and post-breeding.

For a fully mature adult bird, the pre-breeding moult occurs early in the year, before or during northward migration. This moult results in 'breeding plumage.' Here's a Curlew Sandpiper in fresh breeding plumage.



Notice that this moult involves a change of body feathers only, plus, eventually, the tertials and a few coverts. Therefore the majority of wing feathers are quite worn, contrasting with the fresh, pale-fringed body feathers.


Though there is some further replacement of feathers, such as the tertials, inner greater and median coverts and around the chin, most of the change of appearance here is caused by feather wear. As the pale feather fringes wear away, more of the richly coloured feather bases are exposed, causing the development of brighter overall colouration.



Again, relatively little feather replacement has occurred; most of the changes are due to feather wear. This bird is now in peak plumage ready for breeding.


Post-breeding head moult has begun, and a few non-breeding feathers can be seen growing around the breast, while the rest of the plumage is showing the effects of bleaching and extreme wear.

Post-breeding moult occurs pretty rapidly as birds migrate southwards. Here only a few flank and belly feathers, mantle and scapulars, a tertial and the primaries remain of the old feathers. Note the pale fringes of the freshly-replaced feathers.


The post-breeding moult involves the replacement of body, wing and tail feathers, so the primaries are now new. Notice how the condition of the tertials affects the apparent primary projection. Wear continues on feathers moulted earlier (the fringes on the head feathers have now largely worn away). The bird's plumage is now perfectly suited to the muddy colouration of its non-breeding habitat. Eventually this plumage gives way to fresh breeding plumage and the cycle continues.

To see the whole process, please go to this link.