I was able to get out today, further afield and watched a number of migratory Oriental Reed Warblers (Acrocephalus orientalis), common at this wetland site. Many birds were actively feeding ‘together’ today as there were swarms of midges (green coloured non-biting midges that look mosquito-like in the family Chironomidae).
Besides the Oriental Reed Warblers, other birds feeding on the Chironomidae include Pied Trillers (Lalage nigra), Common Ioras (Aegithina tiphia horizoptera), Yellow-vented Bulbuls (Pycnonotus goiavier analis), Paddyfield Pipits (Anthus rufulus malayensis), flocks of Daurian Starling/Purple-backed Starlings (Agropsar sturninus), Sand Martins, Barn Swallows (Hirundo rustica) and Pacific Swallows (Hirundo tahitica javanica).
Some birds were taking the Chironomidae as winged prey, especially the Swallows but the Oriental Reed Warblers were predominately gleaning them from foliage and stems of plants; often reaching upwards or downwards. The activity was fast and they allowed me to watch closely; akin to birds feeding on alate ants or termites. Prey was taken from a height of 1 to 2 meters, as the bird worked its way up and down the bushes. Rarely prey was snatched from the air (Post 2).
None of the Chironomidaewere branch swiped, as they are rather small prey. I once spotted a daddy long legs spider (Pholcidae, cellar spider) taken (above). In the past I have seen Oriental Reed Warblers consume, by gleaning from foliage, three different types of winged Hymenoptera, one of which looked like a Wasp.
The birds were also fairly vocal, once active feeding had subsided (~9.30am). Calls during migration have been well described by Wells 2007 (using his work here). Above is a waveform and sonogram of 4 types of calls I heard; the differences can be better appreciated in the upper waveform. An extended calling (in the same order) of the 4 types of calls are in the SoundCloud link: https://soundcloud.com/amar-singh-hss/oriental-reed-warbler-acrocephalus-orientalis-calls
Calls are generally loud and easily audible; these were recorded with a shotgun mike and camera and then edited. Calls in group 1 are a single discreet ‘tak’; occasionally these may be repeated as 2 calls rapidly together. Calls in group 1 are of a lower amplitude in the waveform but surprisingly of the same frequency as group 1 in the waveform. They sound like the churring “trrrrk” calls. Group 4 has the rolling “trrrak” calls. Group 3 sound like “kirr” (see HBW 2018).
Amar-Singh HSS (Dato’ Dr)
Ipoh, Perak, Malaysia
Location: Malim Nawar Wetlands, Perak, Malaysia
Habitat: Extensive ex-tin mining area with pond/lakes, wetlands, fish farming
Date: 2nd January 2019
Equipment: Nikon D500 SLR with Tamron SP 150-600mm f/5-6.3 Di VC USD, handheld