Raw data for: No reproductive benefits of dear enemy recognition in a territorial songbird

Territorial animals often learn to distinguish their neighbors from unfamiliar conspecifics. This cognitive ability facilitates the dear enemy effect, where individuals respond less aggressively to neighbors than to other individuals, and is hypothesized to be adaptive by reducing unnecessary aggressive interactions with individuals that are not a threat to territory ownership. A key prediction of this hypothesis, that individuals with better ability to learn to recognize neighbors should have higher fitness, has never been tested. We used a series of song playbacks to measure the change in response of male great tits on their breeding territories to a simulated establishment of a neighbor on an adjacent territory. Males reduced their approach to the speaker and sang fewer songs on later repetitions of the playback trials, consistent with a dear enemy effect through habituation learning. However, not all males discriminated between the neighbor and stranger playbacks at the end of the series of trials, and there was evidence that individuals consistently differed from one another in performing this discrimination. We monitored nests and analyzed offspring paternity to determine male reproductive success. Unexpectedly, individuals that learned to recognize their neighbors did not have higher reproductive success, and in fact one measure, total offspring biomass, was lower for learners. Although the general capability to recognize neighbors is most likely adaptive, we speculate that individuals who decrease their responsiveness to familiar neighbors too quickly may be at a disadvantage, perhaps leading to selection for slower dear enemy recognition learning.