Mountain chiffchaff Caucasus, but interbreeding occurs rarely, if ever. The mountain chiffchaff differs from "tristis" in vocalisations, external morphology and mtDNA sequences. Its two subspecies appear to be distinct vocally, and also show some difference in mtDNA sequences. Mountain chiffchaff The mountain chiffchaff or eastern chiffchaff ("Phylloscopus sindianus") is a species of leaf warbler found in the Caucasus ("P. s. lorenzii") and Himalayas ("P. s. sindianus"), and is an altitudinal migrant, moving to lower levels in winter. The nominate subspecies is similar to the Siberian chiffchaff, but with a finer darker bill, browner upperparts and buff flanks; its song is almost identical
The Life of Birds matter had been covered before by Attenborough within "Life on Earth", in an episode entitled "Lords of the Air", but now he was free to expand on it. However, by his own confession, despite being especially fascinated by one family, the birds of paradise, Attenborough was not an expert in ornithology. Nevertheless, the notion of an entire series devoted to the creatures excited him, as he would be able to not only communicate his findings to the viewing audience, but further his own knowledge as well. From the outset, the production team were determined that the sound of birds calling