Age- and sex-related morphological and physiological differences influence escape capacity in House Sparrows (Passer domesticus)

Sexual dimorphism and age-related differences are sources that contribute to morphologic and physiologic variation within animal populations. Measurement of animal performance may indicate whether this variation is functionally relevant. Our study aimed to experimentally test this statement in a captive population of House Sparrows (Passer domesticus (L., 1758)) by examining age- and sex-related differences in escape response and its relationship to several morphological (tarsus, wing, tail lengths, and body mass) and physiological traits (cell-mediated immunity, natural antibodies, complement activity, hematocrit, and stress response). Escape response from a predator is considered a good variable to measure animal performance, because natural selection clearly favours individuals that avoid predators successfully. Our experimental design also aimed to standardize possible confounding factors affecting escape behaviour under natural conditions. We exposed sparrows to short episodes of high predation risk by simulating the attack of a predator and assumed that the capture order of individuals was related to their escape capacity. The optimal strategy was the immediate escape response for all individuals. We found that first-year males were the best escapers. In support of the hypothesis, juvenile males gathered a better optimum of several morphological and physiological characters that related to capture order. Le dimorphisme sexuel et les differences reliees a l'age sont des sources qui contribuent a la variation morphologique et physiologique au sein des populations animales. La mesure de la performance animale peut indiquer si cette variation est fonctionnellement pertinente. Notre etude vise a teste experimentalement cet enoncee dans une population en captivite de moineaux domestiques (Passer domesticus (L., 1758)) en examinant les differences sexuelles et reliees a l'age dans la reaction de fuite et ses relations a plusieurs traits morphologiques (longueurs du tarse, de l'aile et de la queue, masse corporelle) et physiologiques (immunite cellulaire, anticorps naturels, activite du systeme complementaire, heematocrite, reponse au stress). La reaction de fuite en presence d'un predateur est consideree comme un bonne variable pour mesurer la performance animale, parce que la selection naturelle favorise nettement les individus qui reussissent a eeviter leurs predateurs. Notre plan d'experience cherche aussi a standardiser les facteurs confondants qui affectent le comportement de fuite dans les conditions naturelles. Nous avons expose des moineaux a de courts episodes de risque eleve; de predation en simulant l'attaque d'un predateur et avons presume que l'ordre de capture des individus est relie a leur capacite; de fuite. La strategie optimale chez tous les individus etait la reaction immediate de fuite. Ce sont les males dans leur premiere annee qui fuient avec le plus de succes. Les jeunes males possedent aussi de facon optimale un meilleur ensemble de plusieurs caracte;ristiques morphologiques et physiologiques relieees a l'ordre de capture, ce qui appuie l'hypothese. [Traduit par la Redaction]
Introduction Because natural selection favours individuals that avoid predators successfully, predation is considered one of the most important selection pressures in shaping prey behaviour. In fact, numerous studies demonstrated that [...]