The juvenile Long-billed Spiderhunter Arachnothera robusta is inadequately described. Cheke, et al (2001) state that descriptions are “unknown”. Wells (2007) states that juveniles are “inadequately described” and suggests that the juvenile is “expected to lack dark mottling on cap and upperparts, but this needs to be checked”. Cheke and Mann (2020) say that the “juvenile is inadequately described, probably lacks dark crown markings and also, apparently, dark streaking”.
A review of images in the Macaulay Library (2025) for Long-billed Spiderhunter with filters for ‘juvenile’ or ‘immature’ showed only a single image with a limited view of the juvenile. An online search for juvenile Long-billed Spiderhunter images did not bear fruit.
On 06 January 2025 at a site in Ipoh, Perak, Malaysia I observed an adult and a juvenile (self-feeding) Long-billed Spiderhunter. They were feeding on the nectar of Sanchezia nobilis (an exotic introduced from Ecuador/Peru). Plates 1-3 show a comparison of the self-feeding juvenile (left) and the adult (unknown sex). I have attempted to use postures that were similar in both birds for comparison. Lighting was almost identical for both birds and image processing kept to the minimum.
Plate 1.
Plate 2
Plate 3
Key observations on the plumage of the juvenile Long-billed Spiderhunter include:
1. The juvenile’s upperparts are a darker olive-green compared to the adult, especially in the head, face and neck; making the demarcation at the malar region less clear.
2. The juvenile’s underparts are a lighter, less rich yellow compared to the adult.
3. The dark cap mottling (scaling) is present but does not extend as far back as in the adult, and is less contrasting against the darker head plumage.
4. The dark shaft-lines (streaking) on the throat and upper breast are developing, as in the adult; but not as clear due to moulting.
5. The outer tail feather (undersurface) appear tipped white as in adults.
6. Bare parts: Juvenile bill and iris colours similar to adults, although the iris appeared slightly lighter. The juvenile’s feet were fleshy-grey compared to the horn-black of adults.
I am uncertain as to how old this self-feeding fledged juvenile is but at this stage of growth it has already developed dark crown markings and breast streaks. What we require now are descriptions of chicks and dependent fledged juveniles.
References
1. Cheke, R.A., Mann, C.F. & Allen, R. (2001). Sunbirds: A Guide to the Sunbirds, Flowerpeckers, Spiderhunters and Sugarbirds of the World. Helm Identification Guides
2. Cheke, R. and C. Mann. (2020). Long-billed Spiderhunter (Arachnothera robusta), version 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.
3. Macaulay Library. (2025). Long-billed Spiderhunter Arachnothera robusta. Cornell Lab of Ornithology. [online]. Accessed on 06 January 2025.
4. Wells, D.R. (2007). The Birds of the Thai-Malay Peninsula: Vol. 2 (Passerines). London: Christopher Helm.
