Wednesday, September 18, 2013

Migration Molt

The birds have been lying low lately…hiding out.

There are dramatic changes occurring in the woods right now and we're not invited to watch.  Down low in the understory, the birds are transforming into a less colorful presentation of themselves. 

It happens every year, shortly after the young have fledged.  Birds start to replace their bright breeding color feathers with fresh new ones, only now in more subdued shades.  Starting in late July and continuing into the fall migration, birds retreat to the thickets to make their migration transformations in private. 

When they come out there is a noticeable difference. These American Goldfinch are making the change now.

The Hermit Thrush normally has a  tail a third the length of his body.  Losing his tail in a molt would make him look more like this juvenile.  He could be at a disadvantage then, if he had to escape a raptor...I'm sure he senses that, too.   Catching his food  has to be more difficult with his limited flying prowess also, so lying low is his strategy. 
Hermit Thrush, May 2013

Feeling vulnerable while short-on- feathers, birds in general choose to remain hidden in late summer.  Being inconspicuous helps them survive this necessary transition. 

Cautious and careful, this Hermit Thrush flew away as soon as he saw me.

Birds don’t lose all their feathers at once; it’s a gradual process.  Feathers get worn, torn, lost and sun bleached. Summer and winter replacement cycles are necessary and predictable. 

Being largely uninvited to view the adults in transition, the young, on the other hand, have something to show off...their new colors. 

This 1st year Northern Cardinal was changing from a multi-colored fledging into a bright red adult and seemed proud to show it off.   The Northern Cardinal is a year-round resident in Wisconsin and a welcome sight when everything else here is black and white.  

REMINDER: Click any picture to enlarge.

The male Indigo Buntings will lose a bit of luster soon, also.  This one is still quite blue, but he will become blotchy blue-brown as the season progresses…he’ll be in Central America by then. 

One bird that doesn’t change much from season to season is the Black-and-white Warbler.  Its black and white stripes are replaced with black and white stripes, so the transition is hardly noticeable.  For a bird whose nature is to forage up and down tree trunks of a similar stripe, he possesses the perfect camouflage.  

Finally, for a bird with common in his name, the Common Yellowthroat doesn’t deserve such disrespect. This one is a 1st year juvenile just now developing the black mask he will wear throughout his life. It's true, he is common in one sense...he's widespread over North America.  He's not often spotted in the wild, though.  In that way he is similar to a bird in molt...secretive all the time. 


Credit: Cornell Lab of Ornithology, All About Birds
Credit: Sibley Guide to Birds