Why was he murdered? The first report of the motive for conspecific killing in a flock of captive tree sparrows (Passer montanus) through direct video surveillance

In animal societies, conspecific killing is the most extreme way in which individuals resolve conflicts and is rarely reported in the literature. The reasons for such behavior are unclear because the majority of reports present only circumstantial evidence. Herein, we report the first-ever direct observation of conspecific killing in a flock of captive Eurasian tree sparrows (Passer montanus) and our tests of three hypotheses to explain the causes of this behavior in this species: mate guarding, securance of dominance rank, and nest-site competition. Video footage was sampled every 24 h according to the reproductive stages of the attacker's mate, and the recorded aggressive behaviors between the attacker and the victim were analyzed. The attacking behavior of the attacker increased during its mate's fertile period and decreased during the non-fertile period. The male tree sparrows generally fought to guard their mate against other males. This study indicates that mate-guarding behavior during the female fertile period leads to fatal fighting between conspecific males. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo220607et03a and http://www.momo-p.com/showdetail-e.php?movieid=momo220607et05a.

Automated summary

This study reports the first-ever direct observation of conspecific killing in captive Eurasian tree sparrows and tests hypotheses to explain the causes of this behavior. The results indicate that conspecific killings occur during fights between male tree sparrows to protect their mates.