Perverse exercise for the growing pelican

Is it possible that pelicans (https://www.inaturalist.org/observations?place_id=any&taxon_id=4323&view=species) routinely use a benign form of family abuse to train the growth of their super-light skeletons and air-sacs (https://en.wikipedia.org/wiki/Air_sac)?

At first sight, it might seem that

• the infants of pelicans, like other altricial birds, beg vigorously from their parents to demonstrate their fitness to be fed, and
• this is more conspicuous than in other birds, simply because of the sheer size of pelicans.

However, the situation is odder than this.

Please see:
https://www.dnr.sc.gov/wildlife/species/coastalbirds/files/Publications/Sachs2009BehaviorofParentandNestlingBrownPelicansDuringEarlyBroodrearing.pdf
https://brill.com/view/journals/beh/102/1-2/article-p119_7.xml
https://books.google.com.au/books?id=OUderEB-8UkC&pg=PA117&lpg=PA117&dq=Pelican+throwing+a+fit&source=bl&ots=5JY0q-R5Pu&sig=ACfU3U0875nB0d09uFIfajHHf3E4B1CHNg&hl=en&sa=X&ved=2ahUKEwiLgeruz_f_AhWPTmwGHUAuBEYQ6AF6BAg8EAM#v=onepage&q=Pelican%20throwing%20a%20fit&f=false
https://www.pbs.org/wnet/nature/outback-pelicans-video-pelican-tantrums/6451/
https://www.facebook.com/watch/?v=1069970860274746
https://www.youtube.com/watch?v=HLI8Dlx_2Ns
Scroll through https://www.flickr.com/photos/dougbeckers/5042779690/in/photostream/

Please consider the Australian pelican (Pelecanus conspicillatus, https://www.inaturalist.org/observations/22603013).

Juveniles, after and not before being fed, convulse in what looks like a mad rage, throwing themselves around for a minute, and then collapsing to the ground, before snapping out of it - as if nothing has happened - and settling down to their normal snooze.

Parents of the African white pelican (Pelecanus onocrotalus, https://www.inaturalist.org/taxa/4327-Pelecanus-onocrotalus) seize their half-grown juveniles, and shake them brutally, like a terrier killing a rat, before feeding them.

Later, as if to prove that this is not punishment, the workout becomes self-inflicted as the nearly-fledged juvenile of the African white pelican struggles to withdraw its head from its parent's throat. This is an excruciating ritual to watch, because the beak seems to jam, half-open, in the parent's stomach, and both individuals risk being flailed like rag dolls.

The violence of these fits seems at odds with

• the intricacy of the body of pelicans, and
• the touchingly delicate use of the beak-tip to feed the newly-hatched infant.

Pelicans are among the lightest of living birds for their bulk (https://www.lf2.cuni.cz/en/articles/the-legend-of-the-pelican). Consequently, their bones need to have particular resilience.

The hectic experiences of the juveniles of pelicans may therefore be a method of strengthening their growing skeletons and membrane-bound air-sacs.

Publicado el 05 de julio de 2023 por milewski