Sunday, November 23, 2008

Abscission


A strange bird appeared in the back yard yesterday--a new, and first American, species of Pitta?



No, it's a de-tailed Spotted Towhee, Pipilo maculatus. The bird has lot its entire rectricial array (the tail feathers--used for, among other things, aspects of flight). Most likely this resulted from an unsuccessful predatory attack. The predator ended up with a mouthful--or talonful--of feathers, and towhee fluttered away like a winged tennis ball.

I've seen the bird fly--typical short towhee flights, from shrub to shrub, ground to low branch, and it seems to get around okay over these small distances. Towhees aren't big fliers. They are usually on or near the ground, are non-migrant skulkers of edge habitats. They forage by scraping in litter, the back&forth towhee two-step.

One thing the bird can't do now is flash its tail in alarm. Sometimes when startled, towhees fan their rectrices, revealing white spots on the corners of the tail, usually the last things you see as the bird dives into the underbrush.

What happened? My guess is it was attacked by the Cooper's Hawk that has been in the neighbourhood recently. It was in our back yard, sunning in the Japanese maple, a few days ago. Cat is a possibility, but I haven't seen a cat out and about for months.

Spotted Towhee, complete version (i.e., with tail still attached).

I have found towhee tail feathers on the ground a number of times. Towhees may be relatively easy (almost sitting) targets for aerial predators . In a discussion of passerine tail feather loss in Tetrapod Zoology, comments were made on the potential ease at which this can happen in a number of species. One contributor, a bird-bander with nom-de-plume Corvid, mentioned several species that may be more prone to stress-induced tail loss. First in the list was Spotted Towhee. There was no verdict or consensus on whether or not this phenomenon is a sort of defensive autotomy, what happens in certain lizards, salamaders, etc., where the tail fractures and is left behind to puzzle a predator as the rest of the animal escapes.


Whatever happened, this bird has a tale to tell. It just doesn't have a tail.


2 comments:

themanicgardener said...

Keep this up and you'll turn me into a bird watcher.
--Kate

Hugh said...

Aha. My evil plan is working...