Primary bars – an unnoticed identification feature in sparrowhawks?

Accipiter identification is fun yet challenging, and oftentimes require a combination of features. In this article we discuss a potentially useful feature that seems to have been neglected so far.

Sparrowhawks, from the genus Accipiter, are notorious for their identification difficulty. In Singapore, the Japanese Sparrowhawk Accipiter gularis and Chinese Sparrowhawk A. soloensis are commonly observed during migration, while Besra A. virgatus, Shikra A. badius, and Eurasian Sparrowhawk A. nisus make rare appearances for the persevering few. The only resident Accipiter in Singapore is the Crested Goshawk A. trivirgatus. (Fun fact, the Crested Goshawk is placed in a separate genus Lophospiza by some as they are genomically separated from the rest of the Accipiters based on currently available evidence.) A combination of features is always needed in Accipiter identification including wing shape, body shape, and the number of “fingers” (the number of elongated primary feathers). The Crested Goshawk for one has distinctly rounder wings compared to all other Accipiters and is often seen in flight with their heavily feathered “fluffy” undertail exposed. The Chinese Sparrowhawk too is unique in having only four “fingers” with distinct black tips across all ages and a more tapered looking wing. The plumages of Accipiters can of course be identification useful features too, but are too often very similar across many species, especially in juveniles. For example, juvenile Japanese Sparrowhawks have fairly similar underparts to Besra and Shikra (and juveniles of the latter two are almost indistinguishable, unless the yellow eye ring and/or thick black tail bands – diagnostic for Besra at least based on currently understood identification features – are seen). Our individual species pages and visual raptor ID guide cover numerous identification features that can be useful in identifying the raptors in Singapore beyond just Accipiters. However, every now and then, difficult birds show up that push our boundaries and challenge our knowledge of raptor identification. One of the problems that often confuse people is moult – sometimes, Accipiters with moulting primary feathers appear and cause their apparent number of “fingers” to change, causing identification issues. Here’s an example of an Accipiter with six apparent “fingers”. Japanese Sparrowhawk that superficially looks like a Eurasian Sparrowhawk The only Accipiters in Singapore with six “fingers” are the Crested Goshawk and Eurasian Sparrowhawk, but the plumage on this bird is incorrect for a Crested Goshawk, which would never have barred plumage at any age. Its wings are not round enough either. The bird superficially resembles the very rare Eurasian Sparrowhawk, but the body is too small, tail is proportionally too short, and wings do not look massive enough. The photographed bird is instead the common Japanese Sparrowhawk with moulting primary feathers (p4, the 7th finger from the leading edge) that is causing the sixth “finger” (p5; the 6th finger from the leading edge) to look proportionally longer. A similar bird like that showed up last season as well, which caused a fair bit of identification controversy, and the Singapore Bird Records Committee voted that it was likely to be a Japanese Sparrowhawk as well. While researching the identification features of these sparrowhawks, we referred to a collection of reputable field guides and other documentations (e.g. Billerman et al., 2022; Eaton et al., 2021; Ferguson-Lees & Christie, 2001; Puan et al., 2020; Robson, 2014; Treesucon & Limparungpatthanakij, 2018; Wells, 1999 and more; as well as the few documentations online by trustworthy sources), and noticed a seemingly consistent feature that has not been mentioned in any literature before – the number of bars on the primaries of the fingers. The Japanese Sparrowhawk seems to have consistently more black bars, giving the primary wing tips a slightly denser appearance compared to Eurasian Sparrowhawk, and especially so to Besra/Shikras. To examine this hypothesis we examined ~25 online photographs of each of the four species with nice underpart profiles, and counted the number of black primary bars present on each bird. For Besra/Shikra, due to the extreme similarity of their immature plumage, we only selected photographs that were either from reputable observers, or where the diagnostic features (eye ring, tail band) were visible. Additionally, adult Shikras are easily distinguished based on a combination of other features, so we only included immatures for this work. For all species, photographs were only considered if they were taken in Thailand, Peninsula Malaysia and Singapore to avoid any effects of subspecific variation. Proportion of number of black bars on the primary feather p8 across the species we examined. Proportion of number of black bars on the primary feather p7 across the species we examined. Proportion of number of black bars on the primary feather p6 across the species we examined. Our quick survey shows that, indeed, the number of primary barring is a useful suggestive feature in at least distinguishing the Japanese Sparrowhawk...