A puzzling observation of the crested barbet (Trachyphonus vaillantii) raiding a weaver's nests

@spencer_wp @bushboy @tonyrebelo @jeremygilmore @ludwig_muller @richardgill @happyasacupcake @rion_c @johnnybirder @lukedowney

On 1 September 2000, in Ithala Game Reserve (https://en.wikipedia.org/wiki/Ithala_Game_Reserve), I made the following field notes after watching an individual of the crested barbet (Trachyphonus vaillantii, https://www.inaturalist.org/taxa/117135-Trachyphonus-vaillantii) at a colony of the southern masked weaver (Ploceus velatus, https://www.inaturalist.org/taxa/13804-Ploceus-velatus).

The location was a garden next to the house and garage of an official in the reserve.

No individual of the southern masked weaver was present at the start of the sequence of events.

The most remarkable aspect of this encounter was that the barbet announced itself repeatedly by a staccato call I have not heard before, with a kingfisher-like quality to it, the very antithesis of secretive behaviour.

The barbet perched upside down at the entrance to nests, investigating several nests in this way, before entering one nest so that only the tip of the tail was visible.

After more than 10 seconds it emerged.

A male individual (yellow forehead and beak) of the southern masked weaver returned a few seconds later. This did not vocalise, or antagonistically approach the barbet.

And yet, even after the male of the southern masked weaver returned, the barbet had the colony to itself for more than 15 minutes, free of any opposition or mobbing, or even attendance by any group of the weaver.

The barbet went on to investigate several more nests, entering (and presumably eating the eggs in) two more for about 15 seconds each.

The repeated call, made intermittently by the barbet throughout the sequence, was an irritable/irritated type of vocalisation, like an alarm call. However, the barbet was certainly not alarmed; instead it behaved boldly/brashly.

Several other individuals of the southern masked weaver then returned, However, they did not harass the barbet.

A few minutes after the barbet stopped calling, more than 10 individuals of the southern masked weaver (including several males) returned. They investigated the various nests, vocalising excitedly, as if trying to ascertain the extent of any damage.

DISCUSSION

Why did the southern masked weaver not attempt to defend its nests?

My tentative interpretation is that the barbet, being capable of injuring the weaver, was warning the species it was victimising to stay away, while it was busy with its raiding.

Has any reader observed similar behaviour?

Posted on November 01, 2022 10:41 AM by milewski milewski

Comments

You got no pictures of the incident?
The Barbet's behaviour is not unusual - highly aggressive predators with a taste for other birds' eggs - and almost certainly squabs too.
The Weavers' passivity is remarkable however - known snake "indicators", they bravely mob and physically peck even large Boomslangs, Cobras and Mambas raiding their nests.
But perhaps their courage is moderated for avian predators/raiders which are capable of killing them?
My only vaguely similar experience involved a solitary nesting species - a Spectacled Weaver pair, and a Harrier-hawk. The adults very wisely vanished, hiding deep inside the spiny depths of their Phoenix Palm while the hawk cleaned out their nest. Of eggs or chicks I know not.
Once the hawk was done and flew off, it was immediately pursued (at a respectable distance) by Forktail Drongos nesting nearby - but not the weavers. https://www.inaturalist.org/observations/101986679; and an earlier incident probably involving the same players: https://www.inaturalist.org/observations/100459228

Posted by bushboy over 1 year ago

@bushboy Hi Peter, Many thanks for your informative comment. Unfortunately, I do not have any photos.

Posted by milewski over 1 year ago

I have heard the Barbet's "irritable/irritated type of vocalisation, like an alarm call" but never observed any behaviour similar to what you described.

Posted by spencer_wp over 1 year ago

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