His body was found at 14:08 on the 13th of May 2021. Multiple wounds on his neck and head clearly indicated the cause of death.
Even though the perpetrator was gone by then, he was soon revealed. He didn’t know that the scene was recorded by a surveillance camera. The killer was one of the other tree sparrow males living in the aviary. The aggressor attacked the victim at 12:22 and kept on pecking on him for three minutes, until he was dead. The old saying proved true and the killer returned to the scene of the crime and attacked the corpse twice more before it was found.
So, the culprit and the murder weapon were quickly found. But one question reminded: What was the motive for the attack? Three reasons seemed the most likely: competition for the nest site, defending a mate or fighting for dominance. The researchers looked for the answer in the long-term recordings of the group. Attacks on the victim were already happening weeks before the killing. They were most common during the periods when the killer’s mate was fertile (during egg laying and late breeding stage), but much less frequent in other stages of the breeding period, including nest building.
The case report concluded “conspecific killing was most likely associated with mate guarding against potential rivals” and “the fatal attack leading to conspecific killing is fueled by a high level of aggression in the attacker, and this aggression remains even after the victim’s death”. In a sense, it seems that it was a crime of passion.
While in this case I wonder if the killing could have been avoided if the killer and the victim were not trapped in an aviary, adult birds killing each other have also been reported in the wild, for example in other sparrows.
Evolutionary theory predicts that conflicts between males over females should mostly be resolved by displays (e.g. songs) or threatening behaviour, more than by intensive physical fights. Fights can lead to death both directly and also indirectly via injuries, which can easily become infected in the wild.
However, if there is little chance for getting a mate in the future, it might be worth risking one’s life now and fight. In mammals, competition between males for the chance to reproduce seems to be the main reason for adults of the same species to kill each other. However, it seems to be relatively rare in birds and in many cases the evidence is only circumstantial and the motive unclear.
Current technology, like video monitoring and camera traps, may help shed light on many animal behaviours, even most brutal ones, both in captivity and in the wild.
Polską wersję tego wpisu możesz znaleźć tutaj.
Photo by Takashi Yanagisawa via Pixabay