Cuckoos can stomach toxic caterpillars, but it appears they are also impervious to being stung externally, as bird expert Colin Miskelly discovers.
‘Urticating’ refers to hollow spines that have a venom gland at their base. The spines function like a hypodermic needle, injecting poison into any foolhardy animal that ventures too close.
The example referred to in the blog was a shining cuckoo photographed eating furry larvae of the gum leaf skeletoniser moth.
These caterpillars come with a health warning. If they contact human skin, their hairs can cause local pain (sometimes severe) and swollen itchy welts.
Cuckoos are able to eat prey with poisonous spines, as their stomach has a thick mucous membrane that the spines become embedded in.
The membrane is regurgitated, shedding the spines in the process.
The term ‘urticating’ is derived from Urtica, the genus name for stinging nettle plants (and derived from the Latin urere – to burn). There are nine species of Urtica nettles in New Zealand, with the most infamous being the tree nettle Urtica ferox.
As its name suggests, this is a shrub that it is advisable to learn how to recognise and avoid.
Nettles are covered with tiny poisonous spines that provide the plant protection from browsing animals. There are a few animals that have developed ways to overcome these defences, including the caterpillars of red admiral butterflies.
These caterpillars feed only on nettle leaves, and gain protection from their own predators by hiding among the nettle’s spikes.
While red admiral caterpillars are themselves spiky, they are not considered to have urticating hairs. However, other members of the same genus in the northern hemisphere do have urticating hairs.
As a result of posting the previous blog about shining cuckoos eating toxic prey (including monarch caterpillars), I was sent the following remarkable images of a shining cuckoo catching and eating red admiral caterpillars behind a South Westland beach.
The images were taken by Gerry McSweeney of Wilderness Lodge Lake Moeraki on 5 November 2016. They show a cuckoo repeatedly entering a dense patch of tree nettle on the coastal fringe, and flailing about while searching for caterpillars.
The bird was watched for about 45 minutes, and allowed observers to approach within four metres.
Apparently immune to the nettle’s stings, the cuckoo would then land on the nearby beach sand to consume its spiky prey, before returning to the tree nettle for another caterpillar.
The series of images suggest that cuckoos have both internal and external tolerance for urticating hairs.
With many thanks to Gerry McSweeney, Norm Twigge, Nathan Hill, Rob Lynch, Gonzalo Avila and Jeremy Rolfe for their fantastic images providing insights into the ecological relationships between New Zealand’s birds, plants and insects.