23 June 2021

Feathers wear out so birds molt to replace them. Most species molt their flight feathers one pair at a time, losing a matching feather on each side, so they can continue to fly. Not so with swans, geese and whistling ducks. They replace all their feathers shortly after the breeding season in a single annual synchronous molt. During the molt they cannot fly.

Though it seems crazy to lose the ability to fly these large heavy birds are safe on water and unsafe in flight if missing a few feathers. It works for them to lose these flight feathers all at once.

Geese rarely display their stubby wings but you can tell when they’re molting by looking at their tails. Most of the year their flight feathers cover their rumps (left). When molting (right) you can see a white rump patch.

Right now in Pittsburgh Canada geese are in their flightless period that lasts six weeks from mid-June to August. You’ll see them flock in or near large bodies of water, feeding on land and walking to the water to swim to safety. You might even notice they are not at grassy feeding places, such as Flagstaff Hill, which don’t have bodies of water nearby. Such sites are unsafe when they cannot fly.

Have you seen any Canada geese flying lately? No. Because they can’t.

p.s. Goose mitigation plans do not harass geese during their flightless period. The best mitigation is done before they nest. For example, see the Allegheny Commons goose mitigation plan here.

(photos from Wikimedia Commons; click on the captions to see the originals)

14 April 2021

One of the joys of early spring is finding the first Louisiana waterthrush (Parkesia motacilla) of the year as it forages along a stream and sings its loud distinctive song. The bird is so loud that we hear him first then look for movement along the water’s edge. He stands out because he constantly bobs his tail. In fact he bobs the entire back end of his body!

Just half a minute of this video illustrates what I mean.

A few weeks later the spotted sandpiper (Actitis macularius) arrives to walk the water’s edge bobbing the entire back end of his body, too.

Same habitat, same movement. Is there some advantage in drawing attention to one’s back end? Why do these birds wag their tails? I found a partial answer at All About Birds:

… waterthrushes don’t actually wag the tail, they dip (or teeter) the entire rear of the body by moving their ankle joints. This motion is very much like the bobbing of Solitary and Spotted Sandpipers, which share their wetland habitats. It’s been suggested that this habit might either help them avoid scaring off their prey or possibly startle their prey into motion.

— All About Birds, overview of Louisiana Waterthrush

There’s plenty of time to watch them teeter in the weeks ahead. My first Louisiana waterthrush of 2021 was at Cedar Creek Park in Westmoreland County on 30 March. I expect the first spotted sandpiper next week.

Bonus! Here’s a closeup of a Louisiana waterthrush singing:

(photos from Wikimedia Commons; click on the caption to see the originals)

p.s. Others birds pump their tails including eastern phoebes, palm warblers, hermit thrushes, wagtails and pipits. It is not quite the same motion.