Brooks's Leaf Warbler Phylloscopus subviridis Scientific name definitions

“The whole of the Phylloscopi lose colour very much, but their voices and song do not change. Here I may remark that all of these little birds that I have seen in life, and I have seen a good many of them, have notably distinct voices. By the help of the ear it is utterly impossible to confound them.”—W. E. Brooks (1 Brooks, W. E. (1894). A few observations on some species of Phylloscopus. Ibis 36(2):261–268. Close : 264).

Brooks's Leaf Warbler is one of the smaller leaf warblers and is easily overlooked due to its tiny size and subtle plumage, meaning that it is most likely to attract a birder’s attention with its vocalizations and lively habit of regularly hover-gleaning. It is a poorly known, range-restricted species that breeds in a very limited part of the Western Himalayas Endemic Bird Area (EBA), being particularly associated with relatively dry temperate forests in the western part of the EBA, where its known breeding range is largely confined to northern Pakistan and eastern Afghanistan.

The species was described to science in 1872 from specimens collected in winter on the plains of northern India by William E. Brooks over the preceding six years (2 Brooks, W. E. (1872). On a new species of Reguloides. Proceedings of the Asiatic Society of Bengal 1872:148–150. Close ). Brooks, a civil engineer by profession, devoted his leisure time to observing and collecting birds while in Etawah, Uttar Pradesh. His auditory and visual acuity enabled him to distinguish species that confused even the most well-known ornithologists and authors, such as Allan O. Hume. Despite the lack of technological aids, his observations and voice descriptions, especially of the difficult Phylloscopus species on which he was a recognized authority, remain largely accurate even today. Four Phylloscopus and two Locustella species that are currently recognized are based on his observations of birds in life along with careful study of specimens. His writings are characterized by pieces of instructive advice reiterating the importance of field observations: “to know the birds, hear them as well as see them.”

Brooks's observations translated into the first published accounts of the warbler that now bears his name, accurately noting that it arrives on the northern Indian plains about a month later in winter than Hume's Warbler (Phylloscopus humei). Brooks found that his new species frequented lightly foliaged trees, such as the babool (Acacia sp.) that abounded on the banks of the Ganges at Etawah, and was a relatively scarce and silent bird compared to the much more numerous Hume's Warbler. Whereas other ornithologists apparently confounded some specimens, suggesting they were the young of Hume's Warbler, Brooks (3 Brooks, W. E. (1879). Further observations on Reguloides superciliosus and Reguloides humii, also on Reguloides subviridis and Calliope yeatmani, Tristram. Stray Feathers 7(6):475–478. Close : 478) recapitulated the two important features that distinguish it from similar species: “In describing Reguloides subviridis [= Phylloscopus subviridis], I laid great stress upon its peculiar note, and its very clear coronal streak. The coronal streak of R. humii [= Phylloscopus humei] is often invisible.”

To this day, the species is poorly known on its breeding grounds; there is just one, historical, account of its nest, and in consequence virtually nothing is known of its breeding biology. Owing to the species’ relative scarcity and the difficulty of identification from several co-occurring and more abundant, similar-looking congeners, its migratory routes and wintering range are also poorly documented. BirdLife International has currently assessed the species as Least Concern using IUCN Red List criteria, but there is a need to revaluate its conservation status, as it is likely to be negatively affected even by relatively small-scale habitat loss.