SPRING 2001/VOLUME 15, NUMBER 2

Cornell Lab of Ornithology
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House Finch Disease Survey
Project FeederWatch

The House Finch Disease Survey provides a rare opportunity to track the impact of a bird disease
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It's not easy to find out how a disease affects the abundance of a wild bird population or how the behavior of birds can affect the speed with which a disease can spread. But the House Finch Disease Survey (HFDS) provides a rare opportunity to examine both aspects of a wildlife epidemic. This is why the National Science Foundation has funded an expansion of our work with House Finches. FeederWatchers have already seen the revised HFDS data forms, but there's much more to our expanded study.

The combined efforts of HFDS, Project FeederWatch, and Christmas Bird Count participants have enabled us to chart the pattern of spread of the eye disease and the changes in abundance of House Finches. Now we are trying to understand why the disease spread so rapidly and yet still persists years after the disease reaches a new area. That's why, if you walk into the Bird Population Studies section at the Lab of Ornithology, you might see wiggling white cloth bags hanging on hooks on the walls, each holding a newly captured House Finch waiting to be banded and measured, then released. It's also not uncommon to see a newly banded bird being released with a tiny radiotransmitter attached to its back.

It takes a large and varied group of people to conduct this work. In addition to principal investigator André Dhondt and his trusty assistant, Wesley Hochachka, the House Finch team includes veterinarians; microbiologists; mathematical modelers; former PigeonWatch project assistant Véronique Connolly, who manages the HFDS; and me, who performs the minor task of coordinating the field work and collecting much of the data for the team. Dhondt's first goal for me was straightforward yet daunting: catch dozens of House Finches in and around Ithaca, New York, and attach color bands to their legs; in some cases, I also attach small radiotransmitters to their backs. We're identifying individual House Finches so we can find out how far they travel, where they spend the night, and how much time they spend with the same group of House Finches. All of these factors can affect the rate at which a disease can spread from bird to bird. But how do you catch House Finches? We tried various techniques. Our first attemptsusing prebaited walk-in wire cages with a trap door that closes when a bird enters to get foodweren't very effective, even when we put the traps in trees or bushes near feeders. Then we tried mist nets, which worked well when combined with feeders.

The author uses radiotelemetry to follow a House Finch to its roost site in Ithaca, New York. One of the roost trees in the background on the left. photo by Sonia Altizer (2)

With sites scattered around the Lab of Ornithology and other parts of Ithaca, we captured and color-banded more than 300 House Finches this past winter. Our observations at the Lab feeders suggest that as many as 60 to 70 percent of the Lab's House Finches are now color-marked. Véronique has already fielded many calls from Ithaca residents who have reported seeing some of the banded finches at their own feeders, which is exactly what we were hoping for. Now that these birds are individually marked, we hope to track their whereabouts with reports from FeederWatchers.

The next phase of our project will certainly interest any Feeder-Watchers who have ever wondered whether the House Finch that comes to their feeders once a week is the same bird each time. To determine the winter range of House Finches, we use radio telemetry. I attach a tiny radio-transmitter with a backpacklike harness to some of the birds I capture. The radio and harness weigh less than one gram, and they attach in a manner that doesn't impede the bird's flight, feeding, or movements.

How do you track a wild bird? By following the signals emitted by a tiny radiotransmitter attached to its rump with a backpacklike harness. photo by Andrew Davis

This recaptured female House Finch has already been color-banded, which provides important information on its movements and feeding habits .

Each transmitter emits a continuous beeping radio signal at a unique frequency that we can hear and locate with special receivers from a half mile or more away. We track individual finches from one backyard feeder to the next. We can thus determine whose backyard a particular bird goes into and whether it returns to the same yard frequently. Because House Finches spend a great deal of time in suburban areas, people sometimes stop me and ask why I am wandering down the street holding a strange antenna above my head.

With radiotelemetry, I found spots where House Finches accumulate in large numbers, so I set up additional trapping sites. I calculated how far some of these birds range, which can be as much as one to two miles per day. In addition, I discovered at least three separate roosting sites in various places in Ithaca.

The winter roosting behavior of House Finches is interesting. To date, I have not seen any other species roosting with the House Finches, which is contrary to what we expected. And of the few roost sites I've come across so far, all of the trees are tall (more than 30 feet high), thick conifers, often in suburban backyards. The finches seem to use the same roosts night after night. The birds arrive at the roost about two hours before dusk and gather in tall deciduous trees near the roost tree. Their numbers increase from then until about half an hour before dusk. Then the flock appears to diminish as the birds each fly silently into the roost tree and disappear into the thickest part, usually near the top. Once they are in the roost tree, you would never know they were there. They don't move or make any noise once they've settled in for the night.

All of this field work is shedding light not only on the lives of House Finches but on the human denizens at the Lab of Ornithology as well. On occasion, I cause a stir when I bring mist-netted birds into the Lab. In fact, it's easy to schedule a Lab staff meeting. Just bring a live shrike into the Lab, and everyone comes running.