SANTA CRUZ — In the past few years in the city of Santa Cruz, between August and February, massive murders (flocks) of crows span the skies and caw from the trees, whether on their way to hunt for food during the day or on their way back to their roosts in the evening.
“During the fall and winter, crows are less territorial and form large, raucous flocks that roost together at night,” said Alex Rinkert, a Santa Cruz-based avian researcher and biological consultant. “They are often encountered in flocks during the day as well at this time of year compared to the breeding season, when they are more territorial.”
Longtime city residents may have noticed the population of crows swelling over the past few decades as the non-native birds have discovered an endless feast of trash and food scraps to feast on, according to Rinkert.
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“The crow population in Santa Cruz has increased dramatically in the last 30 years, and has shown no sign of plateauing,” he said. “Prior to this expansion, crows were very rarely encountered in Santa Cruz. The crow population in Santa Cruz today is hundreds of times larger than it was historically. Anthropogenic food subsidies in the form of open garbage containers, pet food bowls, and direct feeding by people are contributing to this population explosion.”
The crows of Santa Cruz, which now number in the thousands, display behaviors not found found in other areas, and have adapted to the coastal city in ways that are still a mystery to researchers.
“Their breeding season begins in February when adults collect twigs and greenery for their nest, and ends in mid-June when the last nests fledge,” said Rinkert. “During the breeding season, they are highly territorial but in the fall and winter they are much more gregarious and form large flocks that descend on neighborhoods and roost sites in the evening. Crows, along with other corvid species, have complex social behaviors that scientists are still working to understand.”
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Being a non-native species in Santa Cruz, the growing murders of crows have a negative impact on native animals that already face so many threats in the urban environment.
“As a predator, they have a profound impact on native animal populations,” Rinkert said. “People are most familiar with their predilection for garbage, but they also actively hunt and catch a wide variety of native animals. Not only are they detrimental as a predator, but they also harass hawks and owls, sometimes relentlessly, which may make it harder for those species to exist in urban areas.”
The crows don’t have a natural check in the local ecosystem and because of that, the population will continue to grow ever larger into the foreseeable future.
“Raptors, mammals, and vehicles may pick one off once in a while, but these mortalities have virtually no effect on the population,” Rinkert said. “At some point there will be more crows than there are food resources and breeding territories which will slow population growth, but I think that is still in the distant future.”
Source: www.mercurynews.com