Mist-nets and a molt-limit

One of the main components of our field research on St. George Island is mist-netting. These nets are designed to passively capture birds that are passing through an area, which we then extract, band, and examine in hand. The aluminum band is placed on the bird's leg and has a unique number on it which serves as a sort of social security number. Studying birds in the hand allows us to better age and sex the bird, as well as check their physical condition.

Below is a photograph of one of our net lanes on St. George Island.  If you look closely you can see a line of nets set up in the open path. We have ten nets set up, varying in length from 6 meters to 12 meters. The nets are designed to be invisible to birds.

Monitoring the nets every 10 minutes, we extract any birds and bring them back to our banding station, which is a portable table surrounded by lounge chairs. It typically takes us two to three minutes to process the bird before it is released back into the wild.

Below is a photograph of a male Summer Tanager that we caught on April 22nd. An adult male Summer Tanager is all red, but if you look carefully you will see that the flight feathers of this bird are still green. This tells us that it is a second-year bird, which means it was born last summer. The green feathers are retained juvenal feathers that the bird had when it first fledged. This contrast between old and new feathers is called a molt-limit, and is one of the vital clues we can look at to help age a bird.

Summer Tanagers are neotropical migrants that breed throughout the southern United States. They winter in forested areas of Central America, and on their Spring flight northward cross over the Gulf of Mexico. Close examination of this bird told us that it had burned most of its energy reserves during its crossing.