Re: FW: [canberrabirds] Pelican feeding on Gambusia holbrooki

[Con Boekel <>]

Hi Geoffrey

Gambusia do fascinate me. The species difference between water that has Gambusia and water that does not can be quite large. I am pleased that the JWNR crew have created shallow ephemeral scrapes. Even if they are colonized by Gambusia during floods, the Gambusia die when the scrapes dry up. At other times, in the absence of Gambusia, the temporary water often seems to teem with aquatic life. I believe that this is particularly important for the smaller species of frogs. Well done, those managers!

It is interesting watch the various species of avian fish hunters pursuing Gambusia at Kelly's. The Pelican seems to be almost absurd in the size discrepancy between predator and prey. Apparently the beak capacity of the Australian Pelican, at around 13 litres, is the largest for any species in the world. The Pelicans lunge forward and grab 13 litres of water. They then strain the water out of their beaks before swallowing whatever fish was in the 13 litres of water. The straining process requires a fair bit of energy and they only seem to do it when they know they have a fish - even if only a tiny Gambusia. If there is no fish, they do not strain the water, but simply open their beaks to let all the water out, ready for another lunge.

On another matter, your short Morseby fish and bird lists seem to reinforce the biogeographical connectedness between Aus and PNG.

regards

Con

On 2/2/2018 12:28 PM, Geoffrey Dabb wrote:

Con is clearly a student of Gambusia, an interest I share, possibly the result of a shared tropical years.  In Port Moresby, I think in the late 60s, I had a large aquarium tank I kept stocked with local freshwater fish.  These were obtained by having the warders pull a net through billabongs of the Laloki River that lay within the precincts of Bomana Corrective Institution.  Gambusia were plentiful.  Other exotics include Three-spot Gourami and Tilapia that had bred down in size to less than 10cm (they were much larger in the Sepik).  Being mouth-breeders, they were surrounded by a cloud of tiny fry if caught when a light was turned on at night.  In a few minutes all would have popped back into the distended mouth.  Native fish included Rainbow Fish and Purple-spotted Gudgeon.

 

Common birds of Port Moresby gardens in the 60s and 70s:

 

Figbird (yellow-bellied)

Cuckoo-shrikes (Black-faced and White-bellied)

Fawn-breasted Bowerbird

Rainbow Lorikeet

White-breasted Woodswallow

Friarbird P novaeguinae

Rufous-banded Honeyeater

Black-backed Butcherbird

Singing Starling

Brush Cuckoo

Varied Triller

Sunbird N jugularis

Mannikins (Chestnut-breasted and Grey-headed)

 

 

From: Con Boekel [m("boekel.com.au","con");">]
Sent: Thursday, 1 February 2018 5:09 PM
To: canberrabirds chatline
Subject: [canberrabirds] Pelican feeding on Gambusia holbrooki

 

Mosquito fish Gambusia holbrooki  are an introduced species. Although small, they are rated as a threatening process because of their predatory behaviour. The female may grow up to 40mm.

This morning at Kelly's a Pelican was actively fishing for around half an hour in very shallow water. For much of the time it could only fully inflate its lower beak with water by twisting its head sideways. At times it was possible to photograph the species of fish being caught when the Pelican threw them upwards and towards the throat to swallow them. The only species that were identified were Gambusia. It is reasonably unlikely that the Pelican caught loach, carp or redfin during the half hour. The Gambusia did not look very filling!

At times the Pelican captured plant detritus along with the fish. It was not possible to work out how the bird separated the plants from the fish before swallowing the latter.

The attached image has suffered as a result of the post-processing required to reduce the size to meet COG size limits.

regards

Con

https://www.environment.act.gov.au/__data/assets/pdf_file/0005/576644/mosquitofishinfosheet.pdf