Nest-site interference competition with House Sparrows affects breeding success and parental care in Great Tits

Although interspecific competition is suggested to be one of the major forces dictating community structure, interspecific interference competition for nest sites in birds has been reported mainly from observational studies. Here, we asked whether interference by the larger House Sparrow (Passer domesticus) could reduce breeding success and parental behavior in the smaller Great Tit (Parus major) following clutch completion, by experimentally allowing House Sparrows to access half of the Great Tit nest boxes. Significantly more tit pairs failed to raise young in nest boxes that House Sparrows were able to enter during their breeding period compared to those that were not able to do so, because House Sparrows usurped 77.8% of the Great Tit nests. Great Tits also increased the duration of nest defense in the presence of House Sparrows. As the outcome of interference competition may lead to breeding failure, birds should necessarily evolve ways to avoid nest competitors either by selecting nests that restrict access to their larger competitors and/or by initiating breeding earlier. Conservation efforts should be directed toward attaching a metal restrictor plate around the entrance of nest boxes to prevent woodpeckers from enlarging the entrance and larger species from entering nests.