Would you choose to eat in a restaurant based solely on the cool jazz wafting out the windows and the hip name over the doorway? Or would you instead make a reservation based on reviews, a friend’s recommendation, or the size of the crowd inside?
Most of us defer to the experience of others. After all, great food and service topped off with a pleasing ambiance generates buzz, which in the end saves us a lot of time, money, and disappointment. It turns out that birds filter their choices the same way – not of restaurants, of course, but of breeding territories.
Scientists used to think that birds were primarily concerned with vegetation structure when choosing a nest site. It is, after all, essential to have adequate food and shelter for the rearing of nestlings. However, recent research shows that social information is just as important – if not more important – in the selection of nest sites. Birds have short lifetimes in which to rear as many young as possible. They don’t have time to sample every “restaurant.”
Matthew Betts, from Oregon State University, and his colleagues studied the importance of socially transmitted information on nest-site selection in black-throated blue warblers in the White Mountains of New Hampshire. They looked at whether the warblers investigated vegetation structure (food and shelter), the position of other warblers, or the actions (especially singing) of other warblers when choosing their nest sites.
Betts’s team speculated that if social information were the primary nest-site selection factor, they could replicate that social information through song playbacks or bird decoys, thereby inducing nesting in sites that otherwise had inadequate vegetation structure.
They found that, at the end of the breeding season, both male and female warblers visited sites with playbacks or decoys more often than sites without those social cues. At the start of the next breeding season, males were more likely to settle in sites where they had observed social cues the previous year, while still taking vegetation cues into consideration. And while both experienced and firstyear breeder males settled at social-cue sites, for the most part, only first-year breeder males chose to settle in unsuitable habitats, even when higher quality habitats were available to them. In other words, the youngest males, with the least life experience, were more likely to imitate the behavior of others, rather than relying on life experience.
And as for the females? Well, it appears they let their suitors make the nest-site reservations, choosing sites with inappropriate vegetation structure provided the male was there first.
Betts and his team showed that, far from being a time-consuming research task, nest-site selection can be fast and easy. Song at the end of the breeding season is often a reliable proxy for reproductive success, both because birds will sing to their nestlings and also because poor nest sites are usually abandoned, thus silent. By listening to the songs of successful birds, others can quickly discern the suitability of a nesting site and earmark it for occupation the following spring.
Betts notes that this skill may prove advantageous in the face of rapid climate and habitat change. “If a bird can fly over a broad area and, just by listening to songs, identify ten good places to nest, there’s a real value to that.”