Single fellas who aren’t tied down to any ladies or territories play a small but important role in maintaining threatened bird populations. There are only 2,000 New Zealand hihi birds left, making them particularly vulnerable to both natural disasters and diseases. By sneaking around with females and siring chicks in secret, bachelor birds are actually helping to maintain genetic diversity, according to new work published online in Evolutionary Applications last week.
The hihi, Notiomystis cincta, is so evolutionarily unique that it’s the only member of its family (and that’s not just because it's the only bird species in the world that mates face-to-face). With loss of habitat and introduced predators like rats, the species is only found on New Zealand’s Little Barrier Island. The hihi has been reintroduced to different islands and reserves on the mainland, but even these populations are precariously small. Just one severe event could probably wipe out the whole species.
But now, a team led by Patricia Brekke from the Zoological Society of London has found some hope in an unlikely hero: philandering males. Also called floaters, these wandering bachelors travel between different regions in search of food and mates. Floaters typically boast a lower breeding success rate than males coupled with females, but they also don’t have to invest energy in defending a breeding territory or looking after baby chicks. That’s not a bad strategy for smaller, younger males lacking experience in holding territories or for males of fives years and older who don’t have the energy to defend their space. Sometimes, floaters coerce females into mating with them. Not only do these so-called “extra-pair copulations” increase the number of breeding birds, they also decrease the levels of inbreeding – which can be a problem in pedigree populations.
While the homelessness of floaters makes them difficult to study, the team was able to collect blood samples from a reintroduced hihi population on Tiritiri Matangi Island. This allowed them to assign “true” parentage to offspring. Floater reproduction, they found, is common in this species.
“We have shown that in hihi, floaters are able to reproduce and pass on their genes from one generation to the next,” Brekke says in a statement. “Despite being difficult to study, as they have no fixed abode, we should pay more attention to these bachelor males as they can potentially have a big effect on genetic diversity and therefore the survival of species with very few individuals remaining. Not taking floating individuals into account can undermine our conservation efforts.”