Résumé
Choosing an appropriate partner is a critical decision for many animal
species. However, many mechanisms involved in mate choice are still poorly
understood. Do both males and females choose their sexual partners, do
both sexes use the same criteria for choosing, and do their own phenotype
influence the choices they make, are questions that need further
investigation. Over two successive experiments conducted in captivity with
hand-reared blue tits (Cyanistes caeruleus), we manipulated the color of
the chest plumage, a secondary sexual trait that reflects an
individual's condition, to create two different color morphs (one
pale and one colored). We then tested whether both sexes express a
preference, whether they are attracted to the same morphs, and if the
subjects' own chest color influences the preference they show. Our
data reveal that both sexes are choosy, with females tending to be
slightly choosier than males. We also show that both sexes preferentially
select individuals with a pale chest plumage over colorful individuals,
and this was again more pronounced in females. Finally, paler individuals
tend to be selected by birds that are themselves pale, even if this
phenotype matching was not very robust. Such a preference for paler
individuals is intriguing since mates are predicted to associate with
individuals displaying higher, not lower, value of quality signals. It
could result from adaptive mechanisms related to avoidance of
aggressiveness in confined environment, avoidance of conflicting sexual
signals within individuals, or from cultural mechanisms leading to
preference for individuals that match its own phenotype.