Young male blue tits are not as successful at fathering offspring outside of their breeding pair, not due to lack of experience, but because they are outcompeted by older males. This was reported by researchers Bart Kempenaers and colleagues from the Max Planck Institute for Biological Intelligence in Germany in a study published in the open-access journal PLOS Biology on April 16. Many birds form breeding pairs, and researchers wanted to understand how younger males fare in fathering offspring outside of these pairs.breeding pairs but will also mate and produce offspring outside of that pairing — known as “extra-pair” paternity. Inexperienced males in their first year of breeding are less likely to father extra-pair offspring than adult males, but it is unclear whether their poor performance is because of competition with older males, or because of a lack of skills or experience.
Between 2007 and 2021, researchers studied the breeding behavior of a wild population of blue tits (Cyanistes caeruleus) living in nest boxes in a German forest, using radio-frequency identification technology, behavioral observations, and DNA testing. Then, in 2022, the researchers moved almost all the adult males from the population. They then compared the breeding success of young males in this changed population with data from the previous 15 years. The results showed that in the absence of competition from adult males, 33% of young males fathered at least one extra-pair offspring, compared to just 13% on average in years when adult males were present. The breeding success of young males in this altered population matched that of adult males in normal conditions.
These findings indicate that the reason young males fail to father extra-pair offspring is due to competition with adult males, rather than a lack of experience or maturity.First-year males are often outcompeted by older males for a variety of reasons, such as being more successful in fights over females, investing more energy in extra-pair mating, or being found more attractive by females, according to the authors.
The study suggests that the lower extra-pair mating success of first-year males is largely due to competition with older males. This age effect is influenced by the social environment, at least in the case of the blue tit.
Journal Reference:
Emmi Schlicht, Carol Gilsenan, Peter Santema, Agnes TürThe research study titled “Removal of older males increases extra-pair siring success of yearling males” by K. Andrea Wittenzellner and Bart Kempenaers was published in PLOS Biology in 2024. The study can be accessed via DOI: 10.1371/journal.pbio.3002584.