Grey-rumped Treeswift Hemiprocne longipennis are not uncommon birds in the forest around Ipoh, Perak, Malaysia. Looking back at my records (40) I usually see two to four birds at a time (mode observation). There have been notable exceptions, usually at the forest fringe.
On 4 November 2022 I came out of the forest to find a large mixed-feeding group of swifts, with more than 40 birds together. They comprised:
- Grey-rumped Treeswifts Hemiprocne longipennis 15 (some juveniles)
- Silver-rumped Needletail/Spinetails Rhaphidura leucopygialis 10
- Plume-toed Swiftlets Collocalia affinis 10
- Other unidentified Swifts 5-10
Today, 26 September 2024, I observed at least 20 Grey-rumped Treeswifts together in a tall bare tree at the edge of the forest (Plate 1 shows 18 birds; I observed at least two more further away in the air). They were there when I arrived at 0800hrs and still present when I returned at 1015hrs. They were using the tree as a perch to forage from. Plate 2 is a small composite of four birds.
Wells (1999) notes that Grey-rumped Treeswifts foraging groups may be from 5-50 birds. They are known to band together with other aerial feeders. Duckworth, et al. (1996) reported daily flocks of 15-30 birds at the Similajau National Park, Bintulu, Sarawak and even one report of a flock of 70 Grey-rumped Treeswifts. I do remember seeing more Treeswifts during my three years in Sarawak than I did in the peninsula.
Of interest is that while I was observing them, one female bird flew in to ‘shout’ at a male (Plate 3). I am uncertain if this was her partner or her juvenile. He responded by leaving immediately. I have seen similar social behaviour with the Pacific Swallow Hirundo tahitica.
References
1. Duckworth, J. W., R. J. Wilkinson, R. J. Tizard, R. N. Kelsh, S. A. Irvin, M. I. Evans, and T. D. Orrell. (1996). Bird records from Similajau National Park, Sarawak. Forktail 12:159–196.
2. Wells, D.R. (1999). The birds of the Thai-Malay Peninsula: Vol. 1 (Non-Passerines). Christopher Helm, London.
