Songbirds taught themselves language-like repertoires for territory and mates
Oscine songbirds in suborder Passeri number about four thousand species beside roughly one thousand Tyranni across much of the world. Complex, often learned songs advertise identity, territory, and sexual intent, while scrubbirds and lyrebirds mark the oldest living songbird lineages still singing on Earth today.
Of the roughly 5,000 perching bird species, about 4,000 are songbirds, the suborder Passeri, also called oscines from the Latin for singing bird. Most of the rest are Tyranni, about 1,000 species concentrated in the Neotropics, whose vocal organ has simpler muscles, so their often elaborate calls sound more mechanical. A third branch, New Zealand's Acanthisitti, survives as just two species. Songbirds arose about 50 million years ago, and one of the oldest fossils is Resoviaornis from the Early Oligocene of Poland.
Their family tree points to Australia. Sibley and Ahlquist split songbirds into an Australo-Papuan group and a Eurasian one, but molecular work showed the first was not a true lineage. Passerida, with 3,885 species in 2015, and Corvides, with 812, are sister clades, and 15 further families branching off near the base are almost all Australasian. The oldest living lineage is the lyrebirds and scrubbirds, two species each; the rufous scrubbird now survives only above 600 metres in the Gondwana rainforests of Queensland and New South Wales.
Song mainly announces who and where a bird is and whether it is ready to mate, unlike short calls used for alarm or keeping flocks together. In some populations females favour males with bigger repertoires, and males sometimes sing instead of fighting rivals. Other birds sing too, but a cuckoo's repetition is nothing like a nightingale's or marsh warbler's variety, and even harsh-voiced crows share a soft twitter between mates.
A 2013 study complicated the link between song and brains, finding that spatial learning tends to fall as song repertoire rises.
Source: Songbird
