Tales From The Wilds: Calling All Cuckoos

Yellow-billed Cuckoo reporting for duty

In late winter I started finding egg masses from Gypsy Moths on some of our reforestation trees. The beige colored masses were found on a variety of the young trees, but they were mainly found on Oak Trees. I was removing the masses as I saw them, but what I didn't realize was that there were many more hidden inside the plastic tree protectors that we use on some of the young oaks. The eggs are not thought to survive temperatures below 20 degrees Fahrenheit and during the winter we did have some days well below that temperature, but evidently, there inside the tree protectors, the egg masses were sufficiently insulated from the cold and the eggs managed to survive.

After the tree protector is pulled away, we find the egg masses

Among the eggs masses are the remains of the moths pupa

In the first days of May, just as the leaf buds were beginning to break, the concealed eggs began to hatching and the earliest instar of the Gypsy Moth larvae gathered in tight groups on the tree bark. Soon enough they began making their first forays into the higher branches to munch on the newly unfurled leaves.

The young caterpillars feeding on Oak leaves

A young Gypsy Moth caterpillar on the underside of a Pin Oak leaf

We have had similar outbreaks in the past involving Forest Tent Caterpillars and Eastern Tent Caterpillars - two highly accomplished "defoliaters" of deciduous trees, but we've never had the Gypsy Moth show up like this before. Of course we've never had so many oaks to attract them either. Unlike the tent caterpillars, the Gypsy Moth is an imported species.

As a humane, organic and pesticide-free nature preserve (the only way to be if you want to safeguard your birds and insects), removing egg masses is about as far as I will go to directly combat these moths. My real hope is to enlist the assistance of 2 resident cuckoo species that have a well-known penchant for feeding on hairy caterpillars. In fact the Black-billed Cuckoo and the Yellow-billed Cuckoo are known for deliberately seeking out infestations of these caterpillars and then nesting in that vicinity.

The Black-billed Cuckoo has a red ring of bare skin around its eyes

The Yellow-billed Cuckoo has a distinctive yellow bill and lacks the red eye ring

Most songbird species - even the seed and fruit eaters, switch to a high protein diet of insects during the breeding season. Certainly much of what they feed their nestlings consists of the larvae from a wide variety of insect species. What most birds avoid though are the hairy caterpillars. The hairs of the caterpillars irritate the digestive tracts of most birds and are therefore usually avoided by all except the cuckoos. The cuckoos have evolved digestive systems that can cope with the hairs of these caterpillars.

Black-billed Cuckoo with a hairy tent caterpillar

An aggressive Yellow-billed Cuckoo defends its nest area

At the preserve, I've had some experience with both cuckoo species and have even found a few of their nests. For breeding, the Black-billed seems to prefer overgrown meadows and orchard type habitat, while the Yellow-billed prefers more heavily wooded areas. Their nests are very similar - they are shallow, disk like structures made primarily from long twigs. They actually look pretty flimsy and so it's probably a good thing that the female only lays one or 2 eggs.

The Yellow-billed Cuckoo's nest is a bit like a colander made of sticks

The Black-billed Cuckoo sits on her nest

The Yellow-billed seemed to be more aggressive in defending their nest site. Before I even knew there was a nest, I was accosted by one of the frantic patents which proceeded to put on quite a show in front of me - pivoting back and forth with its long spotted tail, diving from branch to branch and occasionally stopping to give its “tapping on wood” type call, which I have to say – as an alarm call, it’s rather on the subtle side.

The tail of the Yellow-billed is characterized by large white spots

The Black-billed Cuckoo's white tail spots are much less prominent

Over a century ago, John Bartlett Wicks (1836-1915), a local naturalist writer, compared the posture of our cuckoos and the way they moved through tree branches to Passenger Pigeons – a long extinct bird species that Wicks had extensive experience with during his lifetime. The Passenger Pigeons were of a similar size and shape to the cuckoos – and they also shared the behavior of laying only 1 or 2 eggs each season.