Friday, 12 January 2018

Australian Pelican juveniles – strange behaviour after feeding

Recently I was told about the strange behaviour of some juvenile Pelicans after they have been fed. Immediately after the feeding ends many young birds appear to convulse or collapse and then partially recover, only to then go on an uncoordinated rampage where they attack and peck nearby birds or vegetation and sometimes they even peck themselves.

This behaviour is thought to be due to oxygen deficiency as the feeding entails the young bird thrusting its bill and head so far down the throat of the parent bird that its breathing is restricted or perhaps even cut off completely. As some feeding sessions can go on for up to three minutes it is not surprising young birds are starved of oxygen resulting in temporary impairment of their brain and motor control function.

Deb Sullivan, BirdLife Australia, is working on several projects that involve monitoring water birds on the Gippsland Lakes including the assessment of the breeding success and recruitment of colonial nesting species. Since the Pelican rookery is unique and permanent on the Gippsland Lakes the Pelican was chosen as one of the colonial nesting species to monitor.

Regarding the unusual feeding behaviour of Pelicans, here is a quote from Deb describing some of her observations of juveniles feeding:

I observed and timed feeding behaviours over a number of 5 hr sessions at the rookery.  When un-interrupted, the feeding sessions can extend as long as 3 mins. The average un-interrupted feed time was 2 – 2.5 mins. When surrounding birds harassed the adults these sessions were on average 30-40 secs. The birds that feed longer fall over 4 or 5 times before they suddenly launch their demented onslaught on the onlookers. It’s fascinating behaviour. Often the adult will force the young bird onto the ground and hold them there through the feeding process. I have even observed the parents being forced to feed young birds while on the water! As you can imagine the resulting oxygen deprivation leaves the young with their heads hanging precariously in the water, I can’t believe more don’t drown!!

On a recent visit to survey small terns on the Gippsland Lakes we also checked out progress at the Crescent Island Pelican breeding colony.

For more information regarding the Pelican colony see this post:

By early January 2018  this breeding season is drawing to a close with most of the juveniles well advanced and no longer concentrated in tight packed crèches but instead they have spread out along the sand spit adjacent to the breeding area.

A section of the juvenile Pelicans on a sand spit at Crescent Island.

While observing the young birds we noticed a parent bird commence feeding a young one – this was the first time I had seen a feeding session. We were just offshore in a moving boat and it was fully overcast with light drizzle, so conditions were not great for photography. However, I did manage to capture about 25 photos of the session including the post- feeding behaviour of the young bird. The images are a little grainy due to high ISO setting (1600) and cropping plus light drizzle. Seventeen of the photos have been selected to show the event as it unfolded.

Please click on photos to enlarge.

This is the first photo of the feeding session – the feeding had been underway for some time before I could locate the birds and get the camera into action.
The feeding birds are on the right-hand side of the photo. The position of the birds kept changing as the boat moved. 
A photo from another angle as the boat has moved. The young bird’s wings are outstretched for balance. The Silver Gulls no doubt hang around in the hope of some spilt food.
Feeding continues with the young one’s head well inside the parent’s throat.
At this point the parent is about to pull free from the young one and end the feeding session.
The parent moved away, throwing sand up as it departed – no doubt the parent knows what is about to follow. The young one looks a bit odd.

When the parent bird ended the feeding session, the young bird’s head had been inside the parent’s throat for 1 minute and 35 seconds according to the photo times. However my first photo was taken some time after the feeding session commenced, so the full time was even longer.

The surrounding juvenile birds at this point were all moving away to make room for the just-fed bird – I suspect they knew what was coming. The Gulls are looking to see if any food is regurgitated by the young one – in this case there was no stray food for them to scavenge.

The young bird has spun around 180 degrees and is semi prone – nearby juveniles are moving away.

The young one staggers up – a dribble of saliva hanging from its bill tip.
The young bird launches off looking uncoordinated – the head is tilted to the side – the bird’s motor control was certainly impaired.
At this point the bird starts to chase other juveniles.
Its head is tilted again suggesting some loss of control.
Surrounding juveniles are staying clear of the just-fed young one.
The young bird charges off after nearby juveniles.
At this point the young one - on the far left - goes down as if its legs have collapsed.

It recovers quickly and continues the chase. 

The juveniles being chased continue to move away perhaps to avoid being pecked?
This is my last photo of the chase.

Two minutes and eight seconds elapsed from the first feeding photo to the last photo in the above sequence. I did not see the demented juvenile Pelican peck another juvenile - I think by this stage they have experienced this behaviour so many times that they have wised up and know to moved away to avoid being pecked.

The loss of oxygen and resultant loss of normal brain function seems a reasonable explanation for the post feeding behaviour of juvenile Pelicans, however why the birds respond with pecking attacks on surrounding birds, inanimate objects or even themselves is a mystery I suspect. Perhaps the behaviour is learnt and ingrained at a young age when competing for food with siblings – Pelicans usually have two young – when the impulse would be to attack competitors including your sibling?

I should point out that while this unusual Pelican behaviour is new to me it has been seen and noted by many observers in the past.

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