Welcome Swallow taking larval prey from under water.

The following documents Welcome Swallow feeding behaviour I witnessed in July 2012 at the Western Treatment Plant, Werribee (WTP), some 46 km south-west of Melbourne at 38º 02’ 30” S  144º 31’ 05” E. 

Further information came from Glenn Ehmke who saw Welcome Swallows feeding in the same fashion at Fisherman’s Jetty, Anderson’s Inlet Victoria, in July 2007. Anderson’s Inlet is on the coast of Bass Strait, some 120 km south-east of Melbourne at 38º 40’ 18” S  145º 47’ 55” E. Anderson’s Inlet is approximately 130 km east of the WTP, as the raven flies.

The Welcome Swallow Hirundo neoxena is an aerial passerine found across mainland Australia, in New Zealand and on the offshore islands of both countries (Christidis & Boles 2008). On 15^th July 2012 I recorded a group of 20 +/– Welcome Swallows taking larval prey from below the surface of a shallow, clear, brackish pool. None of the pictures taken at the time show any insect or larvae on the surface, or over the surface, of the water. This is believed to be the first documentation of a member of the hirundinidae family in Australia, and maybe elsewhere, capturing prey from below the surface of water.

I would be very interested to hear feedback or observations of other occurrences of sub-surface feeding behaviour by hirundinidae, from anywhere in the world.

The Welcome Swallow is predominantly an insectivorous aerial feeder that is also known, on occasion, to take prey while standing on the ground or from skimming prey from the surface of water. It is a well studied species with HANZAB Vol 7 (Higgins 2006) devoting 27 pages of text and four pages of references to the species. Despite the wealth of information within this and other literature I have been able to access, including an extensive internet search, there appears to be no previous documentation of any member of the hirundinidae family taking prey from beneath the surface of water. It is possible that swallows are already known to feed on sub-surface prey but it is not explicitly stated in readily available texts.

The one possible published exception is the report in Australian Field Ornithology by Lindsay (2012) where a Welcome Swallow was seen to fly from the direction of a eutrophic pool in a streambed while holding a small live fish in its bill, presumably taken from within the water of that pool. As the actual capture was not witnessed it is possible in this case that the fish had been at the surface of the water, or partly or wholly out of pool, when it was taken by the swallow.

It is also possible that some of the previous reports that state that hirundinidae skim prey from the surface of the water mean to include that they take prey from below the surface of the water but I cannot find a reference where this is explicitly stated.

The pool the swallows were feeding from at the WTP was ~ 10 cm to 20 cm deep and about 5 metres long by 2 metres wide. The water in the pool was clear and surrounded by low grasses and succulent herbs. The pool is ephemeral and entirely reliant on rainfall to fill it, including run-off from the nearby road.

Habitat at Western treatment Plant

The morning was partially overcast with a north-west wind blowing. The swallows were facing the wind and diving down and up over the pool, intent on their task, and presenting an opportunity to take photographs from a close range over a small area of water that restrained the very active birds within a relatively small hunting area.

Glenn says the birds at Anderson's Inlet were feeding at the Fishermans Jetty saltmarsh: “I couldn't say for sure what they were feeding on - or that they were actually capturing prey - but I suspect feeding on larvae under the surface is exactly what they were doing. Saltmarshes are renowned for being hugely productive habitats for insect larvae …”.

Habitat at Anderson's Inlet (Glenn Ehmke)

While facing into the breeze the swallows at the WTP hovered ~ 10 – 20 cm above the water and then appeared to strike headfirst at the surface. The closest description of their behaviour is in HANZAB, Vol 7 part B page 1525, where it states: “Sometimes forage by flying low into strong wind, snapping insects, then rising and turning back, then repeating process.” (Higgins 2006). Inspection of photos of the event shows that the bill, and sometimes the head as far as the eye socket, was penetrating the surface of the water and then emerging with an insect larvae. After each attack the head was shaken vigorously, presumably to remove water from the plumage and mouth, and the larvae was then swallowed. Not all attacks were successful. The whole feeding event was quite frenzied and was reminiscent of a flock of tern fishing.

Welcome Swallow with tip of bill in water

Here the head is submerged as far as the forward edge of the eye.  Western Treatment Plant

At Anderson's Inlet the head was again being submerged as far as the eye, possibly beyond (Glenn Ehmke)

In some cases it appeared that the larvae had been taken from just under the surface, 0 mm – 5 mm, because only the tip of the bill entered the water. In other cases, based on the average bill length of a Welcome Swallow being about 10.5 mm (Higgins 2006), they were catching the larvae to a depth of 20 +/- mm as the head was submerged as far as the eye.

At WTP. Here the full bill is submerged and a larvae was captured

Rising from the water the swallow shakes its head vigorously 

The larvae being caught at WTP appear to be about 10 mm long, based again on the average length of a Welcome Swallow bill. One of the more common insects at the plant is a damselfly and in the photos a “fluffy” head and multiple tail spikes can be seen on the prey item suggesting that it could be some sort of damselfly lavae. The prey being taken at Anderson’s Inlet was not seen.

Still shaking the head the prey can be seen in the beak.

Extreme crop of the head to show details of laval prey.

With insect larvae metamorphosing at a set time, it could result in Welcome Swallows gradually learning to take the prey at an ever reducing stage of metamorphose until the larvae were eventually being taken from below the water surface. Over a series of consecutive larval hatching seasons this would presumably not be a difficult learning experience when the numbers of both prey and predator are so common over a comparatively restricted area.

According to HANZAB, Welcome Swallows are migratory with Victorian birds moving north in April and May. Some Tasmanian birds also move north, leaving Tasmania in April on their way to wintering grounds in Victoria, which they then leave to return to Tasmania, beginning in September. As the feeding events reported above occurred in July in coastal Victoria the birds involved were either migrants from Tasmania or some local birds that did not migrate, or a combination of both. As I have not seen sub-surface feeding at WTP other than in July, and Glenn’s sighting was also in July, could it be that sub-surface feeding is a habit learned exclusively by Tasmanian birds and brought to their Victorian wintering grounds? Or is July the only month in which suitable larvae hatch in coastal Victoria? These are questions I cannot answer, and ones that will require more research by someone else.

It would be interested to hear if anyone has similar sightings this year, or in the past, especially from Tasmania or NSW.

Surface and aerial feeding over water, again including taking prey from the surface of water, is described in South Africa for members of the Hirundinidae, especially Grey-rumped Swallow (Psuedohirundo griseopyga), Sand Martin (Riparia riparia) and Brown-throated Martin (Riparia paludicola) (Ginn et al 1989, website 2012, Roberts 2012) but no mention is made of taking sub-surface prey.

A website article (biodiversityexplorer, 2012) states for Brown-throated Martin (Riparia paludicola) in South Africa “It forages in flocks over water bodies with other swallows and swifts, grabbing prey from the water surface.” Again no mention is made of taking of sub-surface prey. The Sibley eGuide to the Birds of North America (2012) notes for the majority of swallows in America “take prey over water”, but again does not mention the taking of sub-surface prey. Collins Bird Guide [Britain and Europe] (Mullarney et al 2001) states for Sand Martin (Riparia riparia) “Rather tied to water, often seen in numbers hunting insects in low flight over lakes and rivers”, but no mention is made of taking prey from beneath the surface.

References:

Christidis, L. & Boles, W.E. (2008) Systematics and Taxonomy of Australian Birds. CSIRO Publishing, Melbourne.

Dolby, Tim, Johns, Penny, & Symonds, Sally (Eds) (2009) Where to See Birds in Victoria, page 109. Allen & Unwin Jacana Books, Sydney.

Gibbon, G. (2012) Roberts VII Multimedia Birds of Southern Africa. Southern Africa Birding CC, South Africa.

Ginn, P.J., McIlleron, W.G. and Milstein, P.leS. (1989) The Complete Book of South African Birds. The Struik Group (Pty) Ltd, Cape Town.

Higgins, P.J., Peter, J.M, & Cowling, S.J. (Eds) (2006) Handbook of Australian, New Zealand & Antarctic Birds, Volume 7: Boatbill to Starlings. Oxford University Press, Melbourne.

Lindsay, K.J. (2012) A possible instance of piscivory in the Welcome Swallow Hirundo neoxena. Australian Field Ornithology 29 166 – 168.

Mullarney, K., Svensson, L., Zetterstrom, D., Grant, P.J. (2001) Collins Bird Guide. Harper Collins Publishers Ltd, London.

Riparia paludicola (Brown-throated martin)

http://www.biodiversityexplorer.org/birds/hirundinidae/riparia_paludicola.htm sighted by JS on 22/09/12.

The Sibley eGuide to the Birds of North America version 7.1, 2012. http://www.mydigitalearth.com/mde/Default.aspx?alias=www.mydigitalearth.com/mde/digital






All images and text are © Jenny Spry and Glenn Ehmke