Birds of Prey

Snail Kite (Rostrhamus sociabilis)

Lake Tohopekaliga, Kissimmee

This snail kite was captured on Lake Tohopekaliga in Osceola County, FL. They have been federally endangered since 1967 which the leading cause for their decline is contributed to developmental pressures and loss of wetlands primarily from agricultural use. Although the population has increased since then they are not safe yet, hence why they are still listed as endangered. Wetland delineation continues to decrease in size and development in Florida is never-ending. To make matters worse, their primary food source, the Florida applesnail (Pomacea paludosa), is disappearing at a rapid rate due to anthropogenic structures that alter water levels. With their primary food source vanishing they were literally starving to death until an exotic species, the island applesnail (Pomacea maculata), was introduced from people releasing them into the wild—disclaimer, do not release your pets into the wild even though it likely saved this bird from extinction. These snails are able to persist because they are tolerable to unpredictable alterations in water levels, especially drought. They are larger than our native counterpart and the snail kites struggled with handling these species, but overall they are adapting to cope with the difference in size.

A potential new threat may find its way to the snail kite through a term we call biomagnification- the concentration of toxins in an organism as a result of its ingesting other plants or animals in which the toxins are more widely disbursed. There is a relatively new discovery of a harmful cyanobacteria (blue-green algae) that persists on hydrilla—an invasive aquatic plant. Most birds that consume this cyanobacteria eventually develop a fatal disease known as avian vacular myelinopathy (AVM) which leads to microscopic brain lesions. Birds that are affected show symptoms of odd behavior where they appear lethargic or are unable to fly or forage properly—most noticeable in American coots and ducks that readily forage on hydrilla when present. These sick birds attract the attention of larger birds of prey such as bald eagles who opportunistically snatch an easy target.

So you may ask, how does this affect our snail kites? In order to answer this question effectively you have to understand the biology of snail kites. They are “specialist,” which exclusively forages on applesnails. Maybe you are already starting to catch on, but applesnails are voracious herbivores which can eat just about any aquatic plant, but where hydrilla is present it usually is in large quantities making it readily available for them to consume. Now that you know what biomagnification means you can relate it to the snail kite: harmful cyanobacteria is present on hydrilla, the applesnails eat the hydrilla, and finally, the snail kite eats the applesnails.

Although AVM has not been detected in snail kites it has killed thousands of waterbirds and other birds of prey including bald eagles, hawks, and owls through the process of biomagnification. It is difficult to detect this disease considering the afflicted bird must be necropsied within 24hrs before the lesions decay. Whether the snail kites have developed some kind of immunity towards this harmful cyanobacteria or it simply has not been detected is yet to be discovered. The fact is that Lake Toho host’s one of the largest breeding populations of snail kites in the state of Florida and if they are being affected by this disease we must make changes hastily. This would likely mean intensive management to eradicate hydrilla which can be costly considering how much hydrilla exists in this environment. Nevertheless, research must be carried out and we need to make an inference before it is too late.

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From Wildlife