Nestling Musings: Do Australian Bushbirds Commit Siblicide?

Little Wattlebird adult & young

UPDATED 31/10/2016
We've played host to a family of Little Wattlebirds in our Sunshine Coast garden. Some interesting observations indicate nestling behaviour I had not thought likely, including possible siblicide (the killing or displacement of siblings in the nest), and how well the young bird manages to conceal itself after leaving the nest.

Little Wattlebird

The pair of wattlebirds built their nest in a hanging basket on our back porch. This was outside a bathroom window and on the main thoroughfare to our home entrance. The birds seemed unperturbed, although we tried to minimise interference by walking around the nest.

Wattlebird eggs

Two eggs were duly laid. Fingers were crossed, because last year the wattlebirds built their nest in a nearby shrub, and the single fledgling disappeared, almost certainly being taken by a kookaburra. I believe one of the reasons for the decline in many bushbird species in suburban and semi-rural areas is the unfortunates habit of people to feed kookaburras and other predatory birds. The handouts may displace some native prey but undoubtedly this boosts populations of avian predators that target nestlings.

Twin wattlebird fledglings

Both eggs hatched, but about a week later, when the youngsters were beginning to look a little robust, one disappeared from the nest. It seemed unlikely to have been taken by a predator because the predator would likely have returned for the second, or taken both at the same time. A dead nestling of some species was found a few days later on the ground about 20m away, but this youngster may have fallen from an unrelated nest. Is it possible that the surviving wattlebird nestling evicted its sibling from the nest? Siblicide is well known among nestling birds, including kookaburras and several waterbirds, but I can't find references to it in relation to Australian passerines (perching bushbirds). Siblicide is evidently a natural way of ensuring that potentially scarce food resources are utilised most efficiently to ensure the survival of healthier nestlings.

Wattlebird nestling

In any event, the survivor continued to do well.  A few days after its sibling's demise, it climbed up to the hanging basket hook. I would put it back in the nest but it kept climbing back up. In this position it was clearly exposed and in danger of being nabbed. However, it flew on stubby wings across 10m of open lawn to land in the canopy of a rainforest tree.

Adult feeding Youngster in Garden

It was striking how over the ensuing days, as the bird gradually became more mobile, it would sit motionless and silent in well-camouflaged roosts in various parts of the garden, high up in the canopy. I had thought nestlings would be begging noisily to be fed and flapping about conspicuously. But usually the only way the young wattlebird could be located was by tracking down the soft calls emitted by the parents during feeding.

Carpet Python

Also in the garden, in another indication that Spring is here, a Carpet Python found its way into the house, entangling itself in wiring behind the computer hard drive.

Wonga Pigeon

A Wonga Pigeon has come into the feeder for the first time.

Yellow-faced Honeyeater

Yellow-faced Honeyeaters have been particularly numerous this year.

White-eared Monarch

White-eared Monarch and Fairy Gerygone were both singing vigorously in creekside dry rainforest near Cooroy: a further sign of Spring.

Eastern Grass Owl near Toorbul: Pic - Matt Harvey

Following our recent successful owling foray, I was alerted to the finding of a dead Eastern Grass Owl near Toorbul, on the southern fringe of the Sunshine Coast, by the road in unusual habitat. One side of the road was introduced Pinus radiata plantation and the other side was an open grazing paddock, with no grassland of any substance in the area. Was this bird in transit?

Sooty Owl in care: Pic - Matt Harvey

Meanwhile, a Sooty Owl was taken into care after being hit by a vehicle near Peachester, in the Sunshine Coast hinterland.

UPDATE ON LITTLE WATTLEBIRDS NESTING 31/10/2016

The young Little Wattlebird referred to was successfully raised. Its parents then built their second nest for the season in a different hanging basket, again on the porch. Again, two eggs hatched and again, one fledgling disappeared.

Brown Tree-Snake

We were on hand when the second fledgling was attacked one evening last week by a Brown Tree-Snake. We rescued the bird, removing the snake to a spot in the garden 30 metres away. Within an hour it was back. We rescued the bird a second time, this time removing the snake to the bottom of the property, 150m away. It nonetheless returned the next night, this time succeeding in killing the nestling.