On Turkey Vultures —flying bloodhounds—Are they more common due to global warming? Or is their increased presence simply, over development and over urbanization?
Early in April (2023) I observed a Turkey Vulture (Cathartes aura) here on LI, Suffolk County, New York. Recently I have seen at least one member of this species, regularly flying overhead, above the canopy of oaks and Pitch-pine in this north shore area. They are a rare sight here, often only appearing in a few numbers much later in the summer. I wondered what circumstances may have caused their attraction to this area, and why so early in Spring?
The species is easily identified. It is a big bird, bigger than a Red Tail hawk and smaller than an eagle, weighing between 4-5 pounds and with a wingspan on average of about 67 inches (1.8 meters). From the ground, its small head and wide black wings with silvery, elongate, patches on the undersides are distinctive. Unlike hawks and eagles, its wings are held upward at a slight angle above the horizontal (dihedral). In flight they generally do not flap their wings, but prefer to soar, often slightly “rocking” left and right as they make graceful turns with wings fixed in a dihedral.
The Turkey Vulture is a scavenger “par excellence”. The species is unusual in that it locates its food by smell alone. Its very well developed olfactory sense is almost unique in the bird world. To facilitate this function, Turkey Vultures have large nostrils in the upper part of the beak which interconnect across the beak, (possibly to increase air flow). Their sense of smell is further enhanced in that their brain has an unusually large olfactory lobe to interpret and detect faint odors. It is claimed that they can scent decaying flesh from miles away.
Once while visiting a neighbor in rural St. John’s County, Florida, my host took me on a tour of his new property. We walked out onto his entrance road where the asphalt entrance drive encircled a 30 foot diameter, surface-water, recharge basin. Enclosed by a high brick wall, this ten feet deep feature was planted densely with Live Oak, Cabbage Palms and closely spaced understory plants. As we approached, I noted the distinct smell associated with the roadkill of a perhaps a raccoon, opossum or armadillo. Apparently to my host’s embarrassment one of these critters had entered the recharge basin, fallen into the water and died there. The vegetation was so dense there was no chance of observation of the source of the smell, either from the road or from above. But when I looked overhead there, circling directly above us were two Turkey Vultures, gliding in a tight circular pattern. I was amazed that they could find their food source so readily, even though their prey was completely hidden from view. Obviously they were using “sent location. My neighbor termed them just “flying bloodhounds”. It is reported that they are attracted to the smell of ethyl mercaptan, a gas given off in the early stages of organic decay. This chemical was routinely added to natural gas pipelines and propane tanks to aid in detection of gas leaks (of a gas with little odor). It was soon revealed that when leaks occurred the scent attracted numbers of vultures to the compromised containers.
Turkey Vultures are large birds which must stay aloft for long periods of time to find their prey. . But for a bird weighing about 4-5 pounds to do so would require great expenditures of muscular effort and enormous caloric input for this essential daily process, if the heavy bird had to flap its wings constantly to remain aloft. For all wild creatures to survive, they must master the the fine balance between the calories they consume (from their prey or food), and calories they expend to obtain and ingest that prey or food. To overcome these exigences of caloric economy, vultures have developed an highly efficient system of seeking out prey, by keeping their wings fixed in place and soaring over long periods of time and over wide distances to locate widely dispersed food sources (roadkill) with little or no effort on their part.
But to accomplish this feat, these large, heavy birds require unstable air conditions. That is, that the lower levels of the air must be warmer than the levels aloft. In these atmospheric conditions air rises in what are termed thermal currents, or simply “thermals”. Thermals are vertical currents of air which rise up over the sun-warmed earth of a plowed field, or that of an asphalt parking lot, or a complex of buildings with dark heat-absorbing roof materials-and other areas which absorb and reradiate solar or other forms of energy.
Vultures use thermals to get aloft and remain there. They can go aloft on one thermal current and then take a long gently sloping glide path down in elevation toward the earth, until they encounter another thermal which they use to carry them aloft again. In unstable air they can remain aloft almost all day and travel over long distances and never have to exert effort which would consume their bodies’ scarce stored calories.
Turkey Vultures are not found in places where “thermals” are uncommon. In the southern part of the USA, where the climate and latitude insure that the earth is heated effectively by the sun, (and they have tall trees for roosting) this species can survive all year long. In the northern states (excluding Alaska) they generally arrive only in the summer months, and in places where topography, as well as natural and man made structures generate adequate thermal currents upon which they depend for survival.
Thus, my question above is: Why have they shown up here on Long Island in the early Spring, a time of the year when the earth is still cool and damp and few thermals occur? But their observed regular presence indicates that for some reason local thermal currents have somehow reached a new level of occurrence sufficient for survival of Turkey Vultures. Are they the “canary in the mine” indicating a warming Earth?.
Can this be attributed to “global warming” as so many other natural phenomena currently are..or can there be other causes?
I suggest here that the argument for other possible causes or co-causes. Thermal activity can be increased as a result of deforestation. Woodlands, here in suburbia are under constant threat of “clearing” for construction. These small forest areas are “heat sinks” which remain cooler than their surroundings, and in general do not generate thermal currents readily.
Then too there is the inexorable suburban sprawl and expansion. Development of more and larger heat-absorbing and heat radiating shopping plazas with huge asphalt parking lots, couple that with more roads , more automotive traffic, more housing development with their dark colored asphalt roofs and heat spewing air conditioners and one can assume that these increase local atmospheric instability and more thermals and increasing areas for Turkey Vultures to exploit.
All these increase ground heat encourage air instability and create thermal current development early in the Spring. Perhaps these —as well as —global temperature changes are encouraging Turkey Vulture arrival earlier in the Spring season than normal.
PS. I have noticed a large number of Turkey Vultures congregating in and around the rapidly expanding complex at the Riverhead Shopping Malls. Turkey Vultures are common there even in the winter. Good thermals from the many buildings and shopping plazas. increased road traffic which may generate more road kill, are all positive developments for this vulture.
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