HERMIT THRUSHES FOLLOW MAGNETIC NORTH TO CANADA

Hermit Thrushes are the only species of the five Catharus family thrushes (brown-backed thrushes, Hermit, Veery, Swainson’s, Gray-cheeked, Bicknell’s) that winters in the US. Their taxonomic cousins migrate on to Central and South America.
Hermit Thrushes are hardier and more cold tolerant than their taxonomic cousins. They can also accommodate more berries and fruits in their diet. They can adapt to a wider range of habitat. Making them one of the most widely distributed North American migratory birds that nest in forests.

Their shorter migration gives them advantages. For one, it is relatively easier to navigate. They have a magnetic compass that they can use to calibrate their north route with daily sunsets. Nightly they slightly adjust their headings relative to the change in sunset direction as the sun sets successively farther northward as latitude increases.

Recent research of this remarkable ability to detect and use the earth’s magnetic field for navigation suggests that birds may visualize the Earth’s magnetic field lines. “Seeing” the field lines seems to be possible through subtle, quantum effects in the birds’ eyes, using short-lived molecular fragments called radical pairs. These radical pairs are formed photochemically in the eyes. It seems that the pairs form a map of the magnetic field. Since we can’t do this ourselves, scientist suggest it is a “dim shape or smudge” that shifts as the birds position changes relative to the inclination of the magnetic field lines. 

Using the shorter distance and accuracy of navigation to their advantage, Hermit Thrushes are first to arrive on the breeding grounds and the last to leave. This makes it possible to have more broods, 2 or 3, than their brown-backed cousins,
All combined, these traits make Hermit Thrushes the only forest thrush whose population has increased or remained stable over the past 20 years.