A new study of wild mountain chickadees suggests that cognitive ability may influence not only survival, but also reproductive success.
Mountain chickadees are small, socially monogamous birds that live year-round in the mountains of western North America. During autumn and winter, they hide thousands of food items across their territories and later rely on spatial learning and memory to recover them. Previous research has shown that birds with better spatial cognition are more likely to survive harsh winters and tend to live longer.
The researchers wanted to find out whether the same cognitive abilities might also affect sexual selection. In particular, they examined whether males with better spatial memory were more likely to father offspring outside their established social pair.
Although mountain chickadees usually form long-term breeding pairs, social monogamy does not necessarily mean genetic monogamy. Females may mate with neighboring males, producing “extra-pair young” that are raised in the nest by the female and her social partner.
The study was conducted in a wild population in California’s northern Sierra Nevada. The researchers monitored hundreds of nest boxes and collected data during the 2018, 2020 and 2021 breeding seasons. They genetically analysed parents and nestlings to determine paternity.
To measure spatial cognition, the team used arrays of eight RFID-equipped “smart” feeders. Each tagged bird was assigned one feeder that would open and provide a sunflower seed. Visits to the seven incorrect feeders were recorded as location errors. Birds that learned the correct location more quickly and made fewer mistakes were considered to have better spatial learning and memory.
Extra-pair paternity turned out to be common. Of the 732 offspring included in the analysis, 222 — about 30% — had been fathered by a male other than the social male at the nest. At least one extra-pair chick was found in approximately 70% of the 127 nests studied. The extra-pair fathers were generally neighboring males, often living around 100 metres from the female’s nest.
Most importantly, cognitive performance predicted how many extra-pair offspring a male fathered. Males that made fewer errors during the feeder task produced significantly more extra-pair young than males with poorer spatial performance.
Among males that fathered at least one extra-pair chick, the statistical model estimated that the strongest performers could father approximately six or seven extra-pair offspring in a year. Males with the weakest cognitive performance were predicted to father only one or two. This pattern was not explained by age: older males were not simply outperforming younger males in either cognition or extra-pair reproductive success.
The researchers also directly compared extra-pair fathers with the social males whose nests contained their offspring. Extra-pair males generally performed better in the spatial cognition tests than the males raising the chicks. Males with better cognitive performance also tended to produce heavier nestlings in their own nests, which may be important because nestling mass is associated with later survival.
The findings support the idea that cognition can become a target of sexual selection. Because variation in spatial cognition appears to be partly heritable in this chickadee population, females mating with cognitively stronger males may potentially pass beneficial traits to their offspring.
One possible explanation is the “good genes” hypothesis: females may gain indirect genetic benefits by producing some offspring with males whose abilities improve survival. A chickadee with a better memory may be more efficient at recovering stored food, more likely to survive the winter and more likely to reproduce over several breeding seasons.
However, the study does not prove that female chickadees directly observe or consciously evaluate a male’s memory. Spatial cognition may be connected to other traits that females can assess more easily, such as physical condition, territory use, dominance, foraging efficiency or vocal behaviour. Better-performing males may also be more successful at locating females or arranging extra-pair encounters.
The results are nevertheless notable because evidence connecting cognitive performance with female mating decisions in wild animals remains relatively rare. Many earlier studies of cognition and mate choice were conducted under controlled laboratory conditions. This research instead combines automated cognitive testing, long-term field observations and genetic paternity analysis in a free-living bird population.
The study therefore suggests that intelligence-like traits can affect several components of evolutionary fitness at once. A strong spatial memory may help an individual survive, raise healthier offspring and father more young outside its social pair.
The paper, “Male chickadees with better spatial cognition sire more extra-pair young,” was published by eLife as a reviewed preprint. eLife’s assessment described the study as important and the supporting evidence as compelling, although the manuscript remains a preprint rather than a traditionally finalised journal article.