Thursday, April 1, 2010

Why are buzzards circling Centennial?

Guest post by Dr. Bob Antibus, professor of biology

Growing up in northeastern Ohio I came to associate the start of spring with the arrival of buzzards back to rocky ledges near the small town of Hinckley. Folks around Hinckley celebrate their annual return with “Buzzard Day” - the first Sunday after the birds return on March 15. This event is celebrated with plenty of pancakes, maple syrup and music.

In recent years I have been asked often about the apparent rise in frequency of buzzards in trees along the Little Riley Creek and on the rotunda of Centennial Hall. In point of fact the birds of interest are not buzzards but turkey vultures. Turkey vultures (Carthartes aura) get their common name from the featherless reddish head and neck which resemble true turkeys.

One of the fascinating aspects of turkey vulture biology is their roosting behavior. Nonbreeding birds assemble in “roosts” or social gatherings. During the winter in southern states these roosts may consist of thousands of birds, but during summer months in the north they typically host a dozen to a few hundred birds. They prefer to roost in trees along streams or in high places like rocky ledges in places with a mix of forest and open fields.

One can see why when Centennial Hall was built it became an ideal spot.

A recent study in Iowa suggests roosts might provide several advantages including: allowing birds to better control body temperature, protection from predators or social communication for food location. If you watch a roost you will sometimes see birds standing awkwardly with spread wings. Biologists think the birds are drying their wings or warming up and call this a “horaltic pose.”

Surviving in nature is all about conserving energy (a lesson humans could learn). Turkey vultures do this by letting their bodies cool down at night. But to fly they must warm up. This explains why they often perch in high places that face east. They catch the early morning sun, again think about this when you see them basking on Centennial Hall.

My favorite aspect of turkey vultures is their flying or more precisely their gliding skills. Being large heavy birds they like to glide into flight rather than lift off. If you have ever seen a turkey vulture fly up from a road kill you know they are clumsy on the ground, especially if they have just eaten a heavy meal.

Hence these birds use their large wings to soar long distances on air currents. I try to get students in my climate change class to observe these birds in the early fall. In fall and spring when we have cool nights the rising morning sun quickly heats open fields and parking lots. This heating leads to columns of surfaced-warmed air rising. Airplane pilots know about these so- called thermals and so do turkey vultures.

They launch from high places in the morning, locate thermals and slowly circle up to much higher elevations. From such high vantage points they spread out in search of food, mostly dead animals. Contrary to my favorite movie westerns, vultures don’t circle dying animals.

In general it appears that turkey vulture populations are on the rise in North America, however some other species in this family are endangered in other parts of the world. If you wish to learn more about these interesting birds I suggest the website of the nature writer Marcia Bonta.

1 comment:

  1. Be assured that Bluffton University's two Hinckley natives are DELIGHTED by our friends taking perch on top of Centennial Hall...especially when it becomes part of the birds' daily ritual during the summer!