Sunday, 6 October 2019

Pacific Gulls scavenging Swan eggs

While monitoring an Australian Pelican breeding colony on the Gippsland Lakes recently we observed a pair of Pacific Gulls taking eggs from a Black Swan nest next to the Pelican colony. A good number, perhaps 50-60, breeding Black Swans were sharing the small island with the Pelicans. One of the Pacific Gulls was also seen with a Pelican egg, however while the egg came from the breeding colony we did not see it taken.

The following notes from “The Shorebirds of Australia – The National Photographic Index of Australian Wildlife” describe the Pacific Gull well in the context of this post:

“…a massive bird, almost as big as a Southern Skua, whose piratical habits it shares. Although its main food is fish and shellfish, it preys on other nestling seabirds, especially during the breeding season. Like most gulls it also scavenges on offal and refuse left by humans.

Like the Herring Gull of the northern hemisphere, the Pacific Gull has a curious habit of dropping turbo shells and other molluscs and limpets from a height onto rocks in order to break them open.”

I noted that each time it was only one of the pair of Pacific Gulls taking an egg as each time the other bird looked on when it could easily have taken an egg itself. Each time an egg was taken the bird flew to a narrow sand spit running south from the breeding island where it dropped the eggs from a height to break them. One egg had to be picked up and dropped a second time to break it.

The pair then consumed the contents of the eggs, though not in peace as a White-bellied Sea-Eagle and later a Forest Raven came in to share the eggs.

It should be noted that the Gull was not taking eggs from a defended nest. Black Swans are formidable foes when protecting their nests and young. The Swan nest looked to be abandoned – possibly because it was too close to the breeding Pelicans. Unattended nests will soon be raided by scavengers in this way – a natural form of population control. Also, as mentioned in the note above, nestlings will be taken if the opportunity arises.

Please click on photos to enlarge.

The pair of Pacific Gulls at an abandoned Black Swan nest. Note the Pelicans and chicks in the background.

A Black Swan egg is seized from the nest. The other Gull looks on.
The Gull can easily hold the large Swan egg in its robust bill. The broken egg in this photo was the first egg we saw taken and broken by dropping onto the sand spit.

The Gull is gaining height before dropping the egg.

The Gulls consuming the first egg we saw taken. I doubt the stolen egg was taken from this Swan’s nest - it showed no sign of attacking the Gulls.  
The Gulls readily gave up the remains of the swan egg for a much larger scavenger, a White-bellied Sea-Eagle.
The Sea-Eagle readily consumed most of the remaining egg contents.

And to clean up the egg remains, a Forest Raven came in. 

There is often interesting activity to observe around breeding colonies, however great care is required to ensure the breeding birds are not disturbed. In this case, we were observing from a boat and a telephoto lens was used to capture the action. Also, the monitoring activities have the appropriate approvals.