Bird migration diversity throughout the year

Some species migrate south in late summer and fall. On a clear or partly cloudy night about a half an hour to an hour after sunset the Swanson’s thrush, a local nesting bird, will take flight going south. It will reach a height of up to 500 feet or more. The species flies south using the stars as a guide.

You can hear their whistle call in flight. On a cloudy night they may not fly at all. Birds come south from as far away as Alaska.

Hermit and varied thrush are vertical migrants coming down from the mountains to the lowlands. The hermit thrush may sometimes winter here but generally stays along the coastal forests of Oregon and California. They migrate by day.

Swallows migrate south when the flying insects become scarce. Tree swallows winter from the Salton Sea into Mexico and Central America. Violet-green and barn swallows go south into Mexico. On mild winters some may stay here.

About 30 years ago, when I was birding in the old settling ponds of Vancouver, Canada, there was a large flock of cliff swallows feeding on flying insects there. Tomato seeds pass through the city septic system and germinate in the sewage area. Because of the heat produced by decaying material, the tomatoes were blooming and doing well. Insects were lured by all of the flowers, providing food for the swallows.

Swifts, like Vaux’s, go south to Central America in winter. One of the most unusual observations I had was about 35 years ago in the spring at Omak, Washington. I was outside of town about 5 p.m., half an hour before sunset, when a large flock of several hundred of these birds were flying in a tight vortex about 500 feet off the ground. They did this for around 10 minutes when suddenly they all dropped in a group into a very large chimney of a schoolhouse. They apparently roosted in the chimney overnight before going north.

Male rufous hummingbirds fly north in March to set up mating territories. They are polygamous and have no interest in caring for offspring. As soon as breeding season ends in June they fly back to Mexico during the day.

Anna’s hummingbird is a permanent resident and stays all year feeding on insects in winter but comes to feeders for sugar water, which may help them survive cold spells.

A group of birds known as rails are weak flyers that migrate close to ground in both spring and fall. They migrate mostly at night and close to the ground to compensate. Some mortality occurs because they are hit by traffic at night. Their flying behavior makes them easy captures by raptors and gulls both in their nesting and wintering grounds.

Somewhat closely related to rails, coots and coot relatives are also poor flyers. If you have ever seen coots take off from water you know they need a running start. Bald eagles capture them both in the water and in flight.

Surprisingly, it has been discovered that smaller tiger sharks love to eat migrating birds in the Gulf of Mexico. This is quite common in both spring and fall when many songbird species migrate in this area. Apparently, the sharks pick off birds that are weak and have fallen in the winter trying to make the 500-mile crossing over water. This trait was discovered when biologists flushed the sharks stomach contents.

Off topic, but a tidbit: On some Pacific islands nesting albatross have problems when their young offspring first learn to fly. The parents abandon the young, leaving them learn to fly and go in the water. Large tiger shark wait just offshore to capture these young as they enter the water. They are weak inexperienced birds and do not know what a shark is, making them an easy target. Black-footed albatross are one of the more common prey items.