This is normal nest behaviour for passerines, and I have many
examples of it recorded it on video. Typically, after being fed a nestling
will reverse itself and present its rear to the feeding adult. The adult
will wait for this, sometimes giving the nestling a nudge to stimulate the
process. Sometimes an adult will visit a nest to collect the sac, with no
feeding. The adult might swallow the sac at the nest, drop it nearby, or
carry it some distance. If more than one nestling presents a sac, the
adult might swallow the first and carry off the second. Some messy
defecators, like Mistletoebirds and Painted Honeyeaters, would be unable to
complete excretion without adult assistance. The practice is said to be
limited to passerines, and that fits my experience. David Cook’s
nesting lyrebird would sometime swallow the sac with its head in the nest, but
more often carry it off. A couple of video frames –
From: David Rosalky [
Sent: Sunday, 2 December 2007 8:55 PM
To:
Subject: Re: [canberrabirds] RE: Would swallow?
Nice
shots, Stuart. I presume this is simply the removal of the faecal
sac of the young. The Noisy Friarbird nest near my house is cleaned by
the adults regularly and frequently. After they bring food, they usually
pick up a deposited faecal sac and fly well away from the nest with it.
(I read in HANZAB that some birds, including Dusky WS for the first days
after hatching, eat the faecal sac.)
This
is an amazing piece of evolution as the young of nidicolous species deposit in
sacs to permit this action by parents. After fledging, the bird's
physiology changes and the sacs disappear.
Apparently,
because of the flimsy nests of the Woodswallows, the parent removes the sac
before it is dropped near the nest thus defeating the purpose of the
clean-up. HANZAB does not actually record such a process of removal from
the anus directly, from my quick scan of the relevant pages.
