In terms of wildlife, the western burrowing owl is a tolerant neighbor to humans. When new houses and roads are built next to the tunnels they call home, these owls put up with the noise and continue to prey on the insects and rodents they eat. But the owls are increasingly on a collision course with humanity.
Developers are always looking for more land to build on, and in places like Southern California, that means moving into the owls’ habitats. To date, most builders have driven owls away by collapsing their burrows, forcing them to find a new place nearby. Still, in highly urbanized environments, the birds often have nowhere to go, putting the future of the species in jeopardy.
As a result, conservationists working with developers are increasingly collecting and transplanting the owls to distant new areas that conservationists believe will meet their needs. However, the evidence that this technique works has been thin. New research published Thursday in the journal Animal Conservation shows that it can be very effective if the birds are tricked into believing that there are already other burrowing owls near the sites where they were transplanted.
The lead author of the new report, Ronald Swaisgood of the San Diego Zoo Wildlife Alliance, knew that developers were reserving land for displaced birds, but noted that there was little follow-up on how the owls were doing.
“Nobody had any idea if these mitigation measures even worked,” he said.
dr. Swaisgood was aware that the birds in California were eligible for classification as endangered and was eager to intervene. He and other conservationists felt that nothing would stop real estate development, including new solar farms. Given the complex situation, he and his team teamed up with the U.S. Fish and Wildlife Service to conduct an experiment with owls found on land that would be bulldozed in the greater San Diego area.
To understand whether the owl transplants were effective, the researchers placed special doors in the colonies’ burrows that allowed the owls to leave but not return. Once the owls were out, all 44 were collected and moved to a new location that already had burrows for them. To help cope with these displaced owls, they were kept in acclimation enclosures for 30 days before being released. Of this group, half were exposed to a little cheating.
The researchers knew from previous work with other species, such as black rhinoceroses, vultures and kangaroo rats, that animals are more likely to settle down if they are taught that conspecifics are nearby.
With this in mind, the team splashed non-toxic white latex paint on the rocks around burrows in the new site that looked like bird droppings on half of the birds. They did this because burrowing owls tend to defecate near burrow entrances, and this technique makes the sites look inhabited. To further support this illusion, an outdoor loudspeaker was set up in these locations to periodically emit burrowing owls the week before the animals were released from their acclimation enclosures, and during the following week.
All this ecological duplicity has paid off. The 22 birds transferred to white paint and call sites quickly settled in, while the other 22 owls all wandered, often making perilous journeys of more than five miles before finding suitable habitat.
The findings are received enthusiastically by other ecologists.
The idea of transplants has long posed a dilemma for ecology experts, said Dan Blumstein, a professor at the University of California, Los Angeles, who was not involved in the study.
“There’s been the assumption that if endangered animals are just moved elsewhere, they’ll be fine, but that’s clearly not always true,” he said. “Experiments like this are essential in figuring out what works and what doesn’t.”
dr. Blumstein and Dr. Swaisgood both hope that transplants from other species will be studied in a similar way to ensure that scientists’ good intentions don’t lead to unnecessary hardship for species already on the brink.