Bring on the Ticks!
The Mad Island bird banding research team is not only interested in the arrival of the Neotropical migratory birds this Spring, but also the tiny parasites and pathogens that the birds may inadvertently be bringing with them. For the second year, the banding crew will not only be banding and releasing each bird captured in a mist net, but also checking birds for ticks and obtaining a blood sample from birds. This will provide data to assess the degree to which migratory birds are importing exotic ticks and tick-borne pathogens from Mexico, Central America, and South America to the United States.
Ticks exist as three active stages called larvae, nymphs, and adults. Each stage requires a single blood meal from a host, during which it will attach to a host and feed continuously for 3-7 days. When the tick is fully engorged, it will drop off the host onto the forest floor or grassy vegetation and molt to the next life stage; this process can take many weeks or months. After that, the tick will emerge and seek another host upon which it can blood-feed.
Ticks don't crawl around too much on their own, and most of a tick's movement is due to the movement of the host to which they are attached. Migratory birds can certainly cover a long distance during the short period of time that a tick is attached, and studies have shown that birds may be important factors in sculpting the distribution of tick and tick-borne disease risk.
Our data from last year indicate that ticks infest about 4% of the migrants that arrive to Mad Island. Key locations where ticks occur are include around the eyes, bill, and inside the ear—these are all locations where its difficult for a bird to preen! We've documented at least 6 different tick species attached to birds, of which only 1 species (Amblyomma maculatum, the Gulf Coast tick) is known to be established in the United States. The other 5 species are established in Latin America. Furthermore, a small number of the exotic ticks arriving with the birds are infected with pathogens that can cause disease in humans.
Most likely, these exotic ticks and pathogens cannot establish here because the climate is too cold or dry, or the right species of hosts for blood feeding are not around. For example, many of the exotic ticks utilize birds as larvae or nymphs, but require anteaters or sloths when they are adults! However, our research team is interested in the scenarios by which these ticks may establish and spread, possibly presenting new public health challenges.
In addition to checking birds for ticks, we'll also be searching for ticks on the vegetation at Mad Island using the drag cloth sampling technique. A drag cloth is a light-colored corduroy cloth that is dragged through the vegetation in an attempt to collect ticks that might be awaiting a host to pass by. Ticks can easily be spotted on the cloth, and removed for investigation.
Stay tuned for future blog entries, where we'll include not only a count of birds we capture, but also ticks we collect! More about the Mad Island project.
This post was written by:
Sarah A. Hamer, MS PhD DVM
Department of Veterinary Integrative Biosciences and
Interdisciplinary Program in Ecology and Evolutionary Biology
Texas A&M University
Research Website: http://vetmed.tamu.edu/faculty/hamer-lab