Rabbits are leaving their stately multi-family houses behind for their own studio apartments in the big city, according to a study published in the Journal of Zoology this week. Because of disease, habitat loss, and hunting, the nearly threatened European rabbits, Oryctolagus cuniculus, have been suffering decline in most rural areas throughout the central part of their native continent. Urban rabbit populations, on the other hand, are getting denser and denser.
An international team led by Madlen Ziege from the University of Frankfurt wanted to know if and how these new neighborhood living conditions affect rabbit social organization and burrow (or warren) structure. So they studied rabbit populations throughout urban, suburban, and rural sites in and around Frankfurt, Germany. They found a total of 191 warrens, and they estimated their sizes based on the number of burrow entrances. Then they rated each for its “urbanity,” Inkfish explains, based on three variables: the number of people living within a half kilometer of the burrow, the number of passersby (and their bikes and dogs) at dawn and dusk when rabbits are most active, and the amount of artificial substrates (like pavement or astroturf) covering the ground. To count how many rabbits live in each burrow, the team tagged some who were flushed out by trained ferrets, and they also staked out warren entrances to tally up the number of those coming and going.
Burrow densities, they found, increased as they moved along the rural to urban gradient. With this increase, they also saw a gradual shift from more complex, accumulated burrows towards smaller, more evenly and widely distributed ones. Additionally, the number of rabbits inhabiting the same burrow decreased with increasing urbanity.
Countryside rabbits lived in extended burrow systems with an average of 32 entrances; larger social groups help them stay protected from predators and conserve heat when it’s cold. The warrens of city rabbits had an average of seven entrances that were both smaller and closer together. And with warmer city climates and lower predation pressures, they could afford to live with fewer roommates.
It’s unclear whether urbanization first led to smaller group sizes and then burrow structures shifted as a result—or if it’s the other way around. In either case, “cities are providing a constant and high food supply through human waste and deliberate feeding, as well as access to vegetation cover, such as shrubs," Ziege tells New Scientist. The structural diversity of urban landscapes may be offering more resources than the open (though agriculturally transformed) rural areas back home.
"It seems they have better habitat quality in the city, so they have better survival rates and reproduce more often and for longer," Ziege tells BBC Earth. I wonder what their broker fees are like.
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