An unsung forest bird - 28th December

We’re mist-netting as much as we can at the moment to make the most of the still weather. Gales are forecast for the next couple of days and apart from checking nests there is very little that we can get done in the cold and rain. We’ve caught a number of un-banded robins in the nets and some tomtit fledglings too, so it’s been successful work.

We also caught some Chatham Islands Warblers. They are modest little brown birds, with pointy beaks whose song sounds like a cheerful jig. Warblers don’t come when we clap our hands or call them and we can’t bribe them with worms to show us their nests.

Chatham Island warblers are common in forested areas all over the Chathams but only live in native forests and can’t survive in habitats that have been modified. Thankfully there is still a lot of habitat like this left in the Chatham Islands, so they are not endangered.

Chatham Island Warbler chick:

They raise one clutch of eggs per year and sometimes are brood-parasitized by the shining cuckoo. The call of the shining cuckoo is one of the signs of spring as they migrate back to the Chatham’s from their winter homes in the Pacific early in the spring. Like other cuckoos, shining cuckoos lay their eggs in other birds’ nests and on the Chathams this unlucky bird is the warbler. The warblers don’t seem to notice that they suddenly have a huge egg in their nests which hatches into a chick much bigger and more demanding that their other chicks. They just work incredibly hard to feed and raise it as if it were one of their own.

But this year the shining cuckoos have been late in their arrival to Rangatira and we’ve only just started to hear them calling now, over a month later than last year. As most of the warblers have already fledged their chicks, the cuckoos will have problems finding a suitable warbler nest for their eggs. It seems that this year there won’t be any poor warbler parents who will be tired out by feeding a giant and hungry imposter.

Due to their accommodating nature, the Chatham Island warblers were the first birds trialed as foster parents for the black robin eggs when there were really few black robins left in the early 1980s. The researchers knew that taking the eggs away from the robins would make them lay another clutch. They hoped that the Chatham Island warblers would be able to bring up the robin fledglings. But as it quickly turned out, warbler parents are not able to supply robin chicks with sufficient amounts of food (robins are after all almost twice the weight of warbler).

The researchers quickly changed their strategy and chose Chatham Island tomtits as foster parents for black robin chicks. Hence tomtits played a significant role in the survival story of the black robins, and as such went down in the conservation history.