• Christopher Stephens, MSc

Orange-crowned Warblers: Caterpillar Catchers!

A perplexing North American songbird explained

Death of a Caterpillar: Spring migration brings hungry Orange-crowned Warblers

Every spring, migrants from the tropics head north to breeding grounds in the Northern Hemisphere. In North America, one such spring migrant species is the Orange-crowned Warbler, Leiothlypis celata. Yellowish green in color, with hints of blue gray, this bird has a subtle beauty, seemingly a leaf come alive as it forages.

When one is birding in North America, especially further North or further West, the sharp, somewhat metallic chip of this warbler, often followed by a long trill gives it away. Easier to see than many warblers due to a preference for lower vegetation than strictly tree loving birds, the Orange-crowned warbler is versatile in its habitat uses, ranging from estuaries, wetlands and shrubby hillsides to urban and suburban areas with sufficient vegetation.

Despite close views, the name might seem wrong to most new birders. Invariably, when leading a birding tour, the visitor, if not familiar with this species would ask me about the “orange” part of the name, surprised to see yellow-green colors dominant. The males actually do have an orange crown of feathers on their head, but they are not prominent. Many encounters with this bird never give one a chance to actually see the orange crown at all.

If the English name of this common spring and fall migrant and summer breeding bird is technically correct, the former scientific name was all wrong! These warblers are now in the genus Leiothlypis, referring to their plainness.

The old genus name Vermivora meant “worm eaters”. In fact, the “worms” that Orange-crowned Warblers eat are not worms at all, but very small caterpillars, often green. Such a predatory encounter can be seen in the author’s photo, taken in coastal lowland forest on Vancouver Island. If you are a human, this bird will brighten your day. If you are a caterpillar, it’s your worst nightmare plain and simple! Real worms, however, are more than safe, being too large to eat and also safely hidden out of view underground. The fact is, caterpillars are incredibly nutritious food for nestlings, but require native vegetation in many cases to thrive. Non-native plants may be toxic to native insects with caterpillar young. Not enough native plants means less birds.

Orange-crowned warblers can be helped out by keeping cats indoors, checking the ground and shrubs for nests before undertaking landscaping activity, and working with local governments and landowners to increase plantings of native shrubs, which provide shelter and attract prey items, especially insects. Working with Vancouver Island University, I published a land use planning guidebook, Planning for Bird Habitat Protection, which contains design guidelines that will benefit this species and many other native songbirds in 2017. Plenty of native plants is the key for native birds!


 © 2020 by Christopher M. Stephens Consulting & Writing

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