Swainson’s Thrush Overwintering at CROW

provided by Clinic for the Rehabilitation of Wildlife

A Swainson’s thrush recovers at CROW after becoming injured during migration.

Flocks of geese organized in V-formations soaring across the sky is typically the imagery that comes to mind when thinking about migration. There are more than three hundred migratory bird species that cross North America twice a year. Migration is genetically predisposed and is necessary for relocation of certain birds during particularly tough seasons. Natural ecosystems are also beneficiaries of migratory travels. During migration, birds will cover a significant area of land on their route South or North. They play an important role in long-distance seed dispersal. With billions of birds making seasonal migrations every year, millions of seeds are transported and dispersed promoting habitat connectivity, especially in fragmented areas. When long-range birds migrate, they can travel as far as 16,000 miles to reach their destination. Even traveling at 30 miles per hour for eight hours a day, it takes some individuals over 60 days to reach their migration destination.

As late fall approaches, northern breeding locations become scarce of resources. Shorter days, limited sunlight, temperature drop, and dwindling food sources are indicators to migratory birds that it is time to fly south for the winter. Long-distance or “high mileage” migratory birds travel on flyways, much like highways, that cross North America. The flyways extend vertically separating into four different paths; the main flyways are the Pacific, Central, Mississippi, and Atlantic. Florida is one of the frequent stopover points along the Atlantic flyway.

It makes perfect sense why a Northern bird would migrate South during wintertime, but one might wonder why a migratory bird spending its nonbreeding season in the tropics would ever go back North. Well, birds migrate South because there is an abundance of resources and when spring returns, migratory birds leave their winter homes to fly northwards where they will breed, nest, raise babies, and take advantage of the regrowth that brings a plethora of food sources. Birds typically return to the same nesting area every year to raise their young.

With this amount of traveling and no access to a map or GPS, it is certainly puzzling how they could find their way to the same destination each year. Astoundingly, birds use compass information from the sun and stars to map their route. Through sensing the earth’s magnetic fields, migratory birds will travel the same course year after year with little to no differentiation.

It is common for a migratory bird to suffer injury or even death along their journey. Migration periods pose threats all birds, like the Swainson’s thrush, in the form of window strikes, cell tower and tall building collisions. On November 15, the Clinic for the Rehabilitation of Wildlife (CROW) admitted a Swainson’s thrush after it had experienced unknown trauma. Upon examination, the patient had swelling around the eyes and dried blood on the lower left eyelid- possible indications of a collision.

The following days showed improvement for the patient. The Swainson’s thrush even passed its flight test; however, it was noted that the patient’s flight was still a bit uncoordinated. Not feeling confident in a full recovery, the CROW rehabilitation staff kept the patient in care. During the additional days in care, the patient had missed migration.

Releasing the patient so it could join the continued migration could do more harm than good considering its physical limitations of a wing droop and uncoordinated flight. Releasing after the migration period ends could displace the patient and render it incapable of catching up with a flock. The best option for the Swainson’s thrush is overwintering until flocks of thrushes travel back north through the Atlantic flyway. Overwintering provides the opportunity for the patient to properly heal in the safety of CROW’s care and be released at the proper time to rejoin a migratory flock heading north.

This Swainson’s thrush is lucky that its injury occurred in a southern location where it can heal away from the harshness of winter. The Swainson’s thrush breeds in the mountainous North and West. Their travels are widespread covering almost the entire United States, northern Mexico, and the Caribbean with their migration route. They will settle in their nonbreeding areas in southern Mexico and Central America. Situations that require a bird to be overwintered in northern territory would force the bird to be housed inside throughout its stay.

At CROW, the recovering Swainson’s thrush can move between the indoors and outdoors. This provides opportunity for the patient to regain strength, mobility, and practice flight coordination in a larger enclosure. When temperatures drop below a certain temperature, the patient is brought indoors to rest and relax.

THIS WEEK AT CROW (12/23-12/29):
There were 65 new patients admitted to CROW’s Wildlife Hospital including five red-shouldered hawks, three eastern screech owls, three brown pelicans, two common loons, a common snapping turtle and a Cooper’s hawk. Recent Releases include four double-crested cormorants, three laughing gulls, a little blue heron and a burrowing owl. Check out a full list of CROW’s current patients and recent releases!

Wildlife doesn’t have health insurance! Your donations help cover the costs of medical and rehabilitative care for over 5,000 patients admitted to CROW’s Wildlife Hospital each year!

Want to learn more about wildlife rehabilitation? Stop by CROW’s Visitor Education Center at 3883 Sanibel Captiva Road.

About Clinic for the Rehabilitation of Wildlife (CROW)
Established in 1968, the Clinic for the Rehabilitation of Wildlife (CROW) is a teaching hospital saving the sick, injured and orphaned native and migratory wildlife of Southwest Florida and beyond.  Through state-of-the-art veterinary care, public education programs and an engaging visitor center, CROW works to improve the health of the environment, humans and our animals through wildlife medicine. For more information, or to plan your visit, go to www.crowclinic.org. If you find an animal that is in need of help, call (239) 472-3644 ext. #222.

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