By Jason Beale, Manager of the Abbott’s Mill Nature Center
Reproduction is a major theme for wildlife in the spring and the signs are everywhere if you take the time to look. It also helps to have knowledgeable neighbors to tip you off to interesting happenings. Paul Layton, a longtime Abbott’s Mill Nature Center volunteer, called me this morning to report nesting Black Vultures and breeding Eastern Spadefoots.
Eastern Spadefoots are toad-like amphibians are immediately recognizable by the yellowish lines along the back and distinct “cat’s eye” with a vertical or diamond-shaped pupil. They also possess a unique sickle-shaped “spade” on the inside of their hind feet. They use the spade to dig into the sandy substrates near ephemeral wetlands that comprise their habitats. This morning, they were singing in a flooded corner of a farm field and in a series of wooded vernal pools. The Eastern Spadefoot is an explosive breeder following periods of heavy rains from spring through fall. Due to the unpredictable nature of their breeding and their underground lifestyle, I consider any encounters very special.
Spadefoots mate using an embrace called inguinal amplexus, grasping the female behind the waist, but in front of the hind legs. While embraced, she lays eggs on submerged vegetation. The eggs hatch in a few days and the development of tadpoles is also rapid with metamorphosis occurring in just a few weeks. This is essential as breeding pools can dry up quickly.
Leaving the Spadefoots behind, Paul took me to an old barn on his property where he has suspected nesting of Black Vultures. They are “B-List” species for the 2nd Delaware Breeding Bird Atlas and any documentation of nesting activity is highly sought. As we approached the barn, a Vulture popped up out of the hole in the roof and flew to a nearby perch.
Taking advantage of the vacant nest, we headed in and discovered a single egg. Nest may be too strong a word as the eggs, usually two, are simply laid on the ground. However, Black Vultures can be fairly aggressive and make a variety of noises which are probably enough to ward of would-be nest robbers.
The large egg, almost 3″x2″, is incubated by both sexes for 32-39 days. The young leave the nest around 10-11 weeks, but are dependent on their parents for another two months.
Back at the Nature Center, I came across a female Brown-headed Cowbird laying an egg in a Barn Swallow nest. While this nest parasite (a bird that lays it’s egg in another bird’s nest) isn’t a favorite among many birders, it was another nest confirmation for the Breeding Bird Atlas.
For more info on amphibians and nesting birds, check out the following:
2nd Delaware Breeding Bird Atlas: http://www.fw.delaware.gov/BBA/Pages/BreedingBirdAtlas.aspx
White, J.F., Jr. and White, A.W. 2007. Amphibians and Reptiles of Delmarva. 2nd ed. Centreville, Maryland: Tidewater Publishers
Baicich, P.J. and Harrison, C.J.O. 1997. Nests, Eggs, and Nestlings. Princeton, New Jersey: Princeton University