American crows are highly social and display some of the most complex and insightful behavior in the Animal Kingdom. Members of the Corvid Family, which also include jays and ravens, American crows are cosmopolitan. They can be found everywhere from rural to urban environments. Many species of crows are well-known for their tool use and, more importantly, their tool-making skills, which puts them at the same, if not a higher, intellectual capacity as dolphins and primates. Crows are also interesting and important animals to study because of their complex social structures and their connections to public health.
Roosts describe both the locations and the large social groups of crows that gather in the evening. These communal groups can be made of hundreds, sometimes thousands of birds from different families and different regions. Pre-roosts often occur, where smaller groups of crows will join each other and then fly together to the roost location. How crows choose roosting sites and exactly why they roost is not well-known, but there are a few theories. One model suggests that during roosting crows transfer important information to one another, while others speculate that roosting reduces the threat of predation. What is interesting to us is how the urban environment might impact their roosting behavior - how often they roost, where and why, may differ in an urban setting considering that at least one factor, predation risk, is usually lower in urban areas simply because there are fewer hawks and other birds of prey.
Crows tend to build their nests very high up in evergreen trees to avoid predation on the eggs. It is hard for terrestrial animals to climb up and be able to balance themselves on the top limbs of a thin-branched tree. Crows start building nests in late winter, usually around February, often building "false" nests in different locations before finally settling on one site to build their real nest. We think they do this perhaps to confuse predators, or to test out different sites before choosing the best one, or to ensure building the strongest nest with the best materials they can find.
With the recent appearance of West Nile virus in the Western hemisphere, the crow is useful in that it serves as a sentinel species. Crows seem to be more susceptible to the virus than other bird species. One of the first indications that the virus has spread to an area is that the crow population is adversely affected. While the virus cannot be transmitted directly from crows to humans, it can be transmitted by the mosquitos that bite infected crows and then bite humans.
The research we conduct on Cape Cod and at BC involves catching crows in Australian crow traps, a large wooden, rectangular structure that allows crows to safely fly in, even rest on perches, but it is impossible for them to fly back out when the trap is set. While crows are omniverous, we usually bait the traps with shelled peanuts because most birds do not figure out that the edible part is the peanut inside and not the shell, while crows understand this keenly. Peanuts in the shell are the perfect bait because when a site is pre-baited (pre-baiting is leaving bait at a site that either does not yet have a trap or the trap is not armed), we can tell whether other animals have been to the site. Such is the case if the peanuts are all gone, including the shells. If crows have been to the site, the shells are left behind. Pre-baiting is an important part of animal capture because arming the trap and waiting to catch crows takes a lot of time and effort, and so we only want to arm the trap if we are fairly certain we will catch what we want to catch.
Once we do catch crows, we put color leg bands on them to identify individuals, and then we release them. Now the most interesting part of the research begins. Going out early in the morning when the crows are most active, we can see which individuals are paired, where they are nesting, what they are using to build nests, how often and what they feed nestlings, etc. At night we might be able to find a roosting site and observe what happens there among individual crows, from which we might distnguish a hierarchy. Once the crows are tagged, we can learn so much about crow sociobiology.
At BC we have been trying to catch crows for a few years now, and recently we noticed that crows have become quite scarce on campus and in nearby neighborhoods compared to previous years. We think this might be because of the pair of red-tailed hawks that appeared on campus in the spring of 2006. Hawks are one of the greatest threats to crows, and so the crows on campus may have been forced to clear out. However, we have not given up and will continue to keep an eye and an ear out for crows.