© 1994-2013 David L. Martin. All rights reserved.See complete copyright statement
Many species of birds make flight calls while they migrate during the night, and I have been recording these calls to follow the fall migration. This page presents some of the data I have obtained during the last six years.
The high-frequency calls (red-brown bars) are usually made by warblers and sparrows.
The mid-frequency calls (orange bars) are made by thrushes and a number of other birds such as Rose-breasted Grosbeak and Scarlet Tanager.
How the recordings are made:
Basically, I have put up a microphone pointed at the sky. The mic output is recorded with a Song Meter autonomous digital recorder.
I record the calls from civil-twilight after sunset to civil twilight before sunrise at sites in Albany County, New York. The first is in a partially developed suburban area in Slingerlands about 8 miles (13km) west of the Hudson River at an altitude of 320 feet (98m). The second is at the Emma Treadwell Thacher Nature Center at Thacher State Park. It is located 7 miles (11.3 km) directly west of and 1000 ft (305 m) higher than my site in Slingerlands. In 2014 I added the Albany Pine Bush Discovery Center. It is located 4.4 miles (7.1km) northwest of the Slingerlands site at an altitide of 350 ft (107 m).
The bird calls are extracted from the sound file by using two free software programs, Tseep-x and Thrush-x, which were obtained from Oldbird.org. Tseep-x extracts short high frequency calls (6,000 - 10,000 Hz) which are produced by warblers and sparrows. Thrush-x extracts mid frequency calls (2,800 - 5000 Hz) which are produced by thrushes, rose-breasted grosbeak and other species. Each of these programs produces many false positives (which result mainly from insect and amphibian calls). I separate the bird calls from the false positives by using GlassOFire (free from Oldbird.org). To identify species, I examine each call's sonogram by using audio editing software (principally Raven Pro), and I listen to some of the calls.