Least Flycatcher: Intimate Neighbors

_{This YouTube video was produced by the American Bird Conservancy.}

The Least Flycatcher (Empidonax minimus) is a small but fierce bird of North American forests, known for its fearlessness in confronting birds much larger than itself, including formidable foes like Blue Jays and even hawks. They often share habitat and compete with American Redstarts, a fly-catching warbler, which they exclude from the best habitat through repeated chases and attacks. Of course, Least Flycatchers defend their territories from their neighbors as well.

However, despite their intense territoriality, these flycatchers are widely known to form dense clusters of breeding territories, even in areas with plenty of suitable habitat. Interestingly, the males closest to the center of a cluster are the healthiest, and the first to find mates. Conversely, birds that don’t join a cluster usually do not mate at all that season! While other factors may contribute to this pattern, the main influence seems to be that it facilitates birds mating with their neighbors in addition to their social mate.

Least Flycatchers are socially monogamous, pairing with a single bird during the breeding season with whom they defend a territory and raise young. But these birds are also quite promiscuous. More often than not, the nest of a mated pair will have at least one nestling sired by another male. “Spreading the love” in this way benefits both males and females — females end up with more genetic diversity in their nests, while males don’t have all their eggs in one “basket,” in case a nest fails. This breeding system, where territories are clustered together, females seek matings outside of the pair, and paired males compete for each other’s mates, has been described as a “hidden lek.” In some ways, this system is quite similar to the communal display areas, or leks, where birds like Lesser Prairie-Chicken and Greater Sage-Grouse defend small arenas to display for females.

One big difference between a classic lek and the so-called “hidden lek” of Least Flycatchers is that both the male and female in a pair are looking to mate with other birds without their own mate knowing about it. Also, the displays are a bit less dramatic. Rather than elaborate plumages, dances, and bizarre methods of sound production, these drab males instead opt to sing the same monotonous two-note song several thousand times an hour.

Also known as: Chebecker, Mosquero Mínimo (Spanish), Mosquerito Chebec (Spanish), Papamoscas Chico (Spanish)

Learn more at https://abcbirds.org/birds/least-flycatcher/