Wednesday, June 10, 2015

The Boat-tailed Grackle

While working at Stone Zoo near Boston in the World Bird Sanctuary’s bird show we come into a lot of contact with wild birds. 

A Boat-tailed Grackle soaring over the Stone Zoo amphitheater (photo: Mike Cerutti)

Our stage is almost surrounded by trees.  This makes for good shade and a pleasing look, but those trees are home to the native birds in the area.  One of the most common birds we see around our theatre is the Boat-tailed Grackle. 

Even though this is my fourth year doing the show here near Boston, this year it occurred to me that I don't know very much about these Grackles. 

These are massive tailed, large songbirds that are mostly a glossy black.  During the breeding season the females turn more brownish while keeping a glossy black head.  The males develop a blue shimmer to their glossy black heads during the same time. 

Male Boat-tailed Grackle (photo: wikipedia)

They have an interesting mating system called a "harem defense polygamy."  This means that many females will all make nests very close to each other and the males will fight over all the nests….this helps defend against predators.  The winning male has the right to mate with all of the females and defend the territory.  However, DNA testing has proven that some of the females will breed with other males away from the harem with a separate male and return to lay the eggs.  The same DNA tests show that on average, only about 1/4 of the offspring actually belong to the male that defends the territory.

Female Boat-tailed Grackle (photo: wikipedia)

Grackles will eat just about anything they can find, including worms, grasses, seeds, bugs, small amphibians, garbage, fruits, and more.  They usually forage on the ground for their meals.  They are one of the few species that will eat Japanese Beetles—a real plus for a bird species that is sometimes considered a “pest.”

Boat-tailed Grackles live on the Atlantic Coast and Gulf Coast of North America.  The wild population is estimated at around 2 million individuals.  Urban development of their territory does not seem to affect these birds.  These birds are adaptable enough to thrive around humans, zoo animals, and all of our hawks, eagles, and owls.

So, if you live along the Atlantic Coast, Florida, or the Gulf Coast, and you see a big glossy black bird with a really long tail, chances are that you are seeing a Boat-tailed Grackle.  If the bird in question has a fairly normal sized tail, it may be a Common Grackle.  Since these birds’ territories overlap, the tail is the key identifier for most people.

Submitted by Mike Cerutti, World Bird Sanctuary Naturalist/Trainer

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