This past Friday, I joined a few friends in Lang'ata, Nairobi, for a leisurely few hours of birding (with masks on!). The birding was great and we ended up with 80 species on our list. We had several very nice sightings, but the day's highlight was a sighting that involved two birds that took even the most experienced of us by complete surprise. The birds in question were Parasitic Weaver Anomalospiza imberbis and Stout Cisticolas Cisticola robustus.
Seeing the birds themselves was not a surprise. The Stout Cisticola is a common resident and the Parasitic Weaver is fairly regular in Nairobi during and just after the rains. What surprised us was the interaction between them.
An intruder in the nest
First, a quick background on the Parasitic Weaver to give you some context. Parasitic Weaver is also called the Cuckoo Finch. It is neither a weaver, a cuckoo nor a finch. It belongs to the family of Whydahs and Indigobirds (Viduidae). Birds of this family are brood parasites. The female lays her eggs in the nest of another bird species and then flies off never to be seen again. When the chicks hatch from the eggs, they will be raised by the 'host' parents as if they were their own young. (For more on brood parasites, see this previous blog post).
On this particular day, the Parasitic Weaver that we saw was a juvenile in the company of a pair of Stout Cisticolas Cisticola robustus that were busy feeding it. Clearly its foster parents. There was also a juvenile Stout Cisticola, which seemed to have been raised together with the parasite. Whydah juveniles are fairly gentle to their hosts. Unlike Cuckoos, which kill the host's offspring in order to take full control of the host parents' attention and resources.
Seeing the Stout Cisticolas feed the young Parasitic Weaver was already amazing by itself. It was in fact the first time any of us had ever seen this (mind you, there were some birders in the group with decades of experience!). But the real surprise was yet to come.
A surprise discovery
Initially, the cisticolas were feeding the Parasitic Weaver with smallish insects that it could easily swallow. And then, all of a sudden, one of the cisticolas flew in holding a huge stick insect! I remember thinking to myself that the cisticola had made a miscalculation and 'bitten off more than the young bird could chew'.
What the birds did next totally amazed us.
The cisticola handed the stick insect to the young cuckoo-finch. The young bird, rather than trying to eat the thing as a youngster would usually do when handed food by its parent, patiently held the insect in its beak. The cisticola then proceeded to pluck each leg off very methodically, one by one. Once all the legs had been removed, the cisticola took it back from the chick and then helped it to reposition it in its beak, after which the chick proceeded to swallow the insect.
What was so fascinating about this was the cooperation between the two birds. They coordinated the whole process so well and in harmony that you would have thought they had discussed it before they did it. The fact that these were two different species makes it even more impressive. I recorded the whole thing on video. Watch it below.
Stout Cisticola feeding stick insect to Parasitic Weaver
Apart from this behaviour being undocumented, it also turns out that the Stout Cisticola is not on the list of birds known to be used as hosts by the Parasitic Weaver (listed in The Birds of Africa Volume 7)! This is one of the reasons why birding is so addictive. Birds are unpredictable and you just never know what to expect!