First documented at DeGray Lake, Arkansas in 1994, the neurologic disease Avian Vacuolar Myelinopathy (AVM) has been implicated in numerous deaths among waterbirds and their avian predators. Currently, the disease has been confirmed in six species of waterfowl, two bird of prey species and one shorebird. A trend in deaths of the affected species has been noticed in the fall/winter seasons of various southeastern reservoirs. One particular reservoir on the Georgia – South Carolina Border has seen some of the greatest numbers of deaths across water bodies affected.
J. Strom Thurmond Lake (JSTL), a 28,000 hectare reservoir, has seen over seventy-five bald eagle deaths since 1998, many of them with confirmed or suspected AVM diagnoses. This lake is dominated by hydrilla (Hydrilla verticillata), an invasive aquatic plant known to harbor an epiphytic cyanobacterium linked to AVM. Unfortunately, hydrilla has also become a resource for many waterbird species in a reservoir with few native species to speak of.
Brigette Haram, a Ph.D. student from the Warnell School of Forestry and Natural Resources of the University of Georgia, is currently investigating the effect of hydrilla on avian distribution at J. Strom Thurmond Lake and the potential susceptibility for different species to AVM on this reservoir. A historically important bald eagle nesting area, this reservoir has shown a decline in successful nesting territories since the introduction of hydrilla in the late 1990’s. Preliminary data collected by Haram suggests the hydrilla infestation on this reservoir is creating an ecological trap for waterbirds and bald eagles that winter and breed there.
The research of Haram, accompanied by Dr. Susan Wilde, involves assessing hydrilla and waterbird distributions on Thurmond to determine if hydrilla infestations create ecological traps for birds using the lake, including bald eagles. Their data from 2012 and 2013 show American coots and other waterfowl congregate in areas with moderate to heavy hydrilla infestations. Aerial surveys have also shown higher bald eagle numbers in these areas and several eagle deaths were recorded near hydrilla sites. Survey data on Thurmond from 2012-2014 show a marked decline in bald eagle numbers from November – January of each year. Future research plans involve installing satellite tracking units on JSTL bald eagles at the start of the AVM season (October-November) to determine if the eagles leave the area, stay and survive, or perish on the lake. Dead eagles will be analyzed to determine if AVM is the cause of death and, therefore, if hydrilla plays a part in the ecological sink that appears to be occurring at the reservoir. This information will help resource managers implement hydrilla control strategies.
The team is also investigating American coot carcass scavenging to determine the range of species affected by AVM. Coots collected from a non-AVM site are used as bait under motion sensing cameras in areas on Thurmond where coots are found to congregate. Data from the first season (2013) documented raptors as well as mammals feeding on the bait. This study will continue, and has so far confirmed some species suspected to be at risk, and added some new species to the list. These findings will hopefully help steer future research on AVM and improve our understanding of the scope of species at risk.
Research in the Wilde lab at UGA is also working on isolating the AVM toxin from the hydrilla/cyanobacterial complex. The research team have made great progress and are preparing to start laboratory trials later this year to test purified extracts from AVM positive cyanos. Once isolated, the nature of the toxin and the mechanism by which it affects brain tissue of birds can be further studied.
Much of the work completed by Haram and others at the Wilde UGA lab has been funded by the Aquatic Plant Management Society and many of it’s regional chapter including the South Carolina Aquatic Plant Management Society.
If you would like to learn more about Haram’s work, AVM, or the work of others with the UGA Wilde Lab, visit their website
For more information on the Aquatic Plant Management Society, visit our website.
Stay tuned for more from the APMS Blog!The APMS Blog is prepared by Dr. Brett Hartis, NC State University