Nature Watch: Night Flight
About the author: Steve Ellis is a naturalist and Land Trust member who enjoys sharing his love of the natural world. His blog series, “Nature Watch,” will appear each month in “Habitchat,” chronicling native plants and wildlife you can expect to see during that particular time of year. We thank Steve for sharing his passion, illustrating the importance of island conservation.
Vast multitudes of birds in Mexico and Central America are readying for a long journey. They’ve molted old, worn feathers and have engaged in an orgy of feeding called hyperphagia. Migration time is here.
Deciding the right time of day to fly is critical for successful migration. Hawks, swallows, and hummingbirds choose daylight hours, while shorebirds and waterfowl migrate both day and night.
Most songbirds, including thrushes, sparrows, flycatchers and warblers elect to fly at night. There are several reasons that make flying after dark attractive. Some species have a star chart in their brain used for navigation. Few predators are out at night and the air is often calmer than during daylight hours, making flight easier. Overheating and dehydration are greatly reduced in the cool air. Lastly, night flight allows for daytime feeding.
Millions of birds participate in spring migration. It’s estimated 70% of North American breeding birds migrate, with 80% of those doing so after dark.
The night flight often begins at dusk; perhaps the setting sun is a navigational tool. Peak migration is from 11:00 PM to 1:00 AM. Birds are usually found at altitudes of 2,000 to 5,000 feet, with some reaching as high as 21,000 feet. Migration is heaviest from mid-April through mid-May.
Weather radar has opened a window on this incredible phenomenon. You can check the progress of nightly migration by going to the BirdCast website (https://birdcast.info/). The site has forecasts of bird migrations and live migration maps. Entering a geographic location will show how many birds are overhead and a best estimate of which species are involved.
On calm evenings, those with acute hearing should be able to hear the contact calls made by birds overhead. The rest of us must rely on radar tracking of the night flight.
Fauna: Orange-crowned Warbler (Vermivora celata)
Among the many migratory birds winging their way northward is a collection of species known as warblers. The name derives from a superficial resemblance to European species that warble.
Orange-crowned is one of the earliest warbler species to reach our area, with a handful overwintering here.
They are five inches in length, with a long, thin bill. Females are olive green, while males are a brighter yellow with an orange patch on their heads. This patch is usually hidden except when the bird is excited or agitated.
Male Orange-crowned Warblers begin singing in April. Best catagorized as a trill, the song rises slightly and then drops downward at the midpoint. It’s been described as sounding “tired.”
Their preferred habitat is brushy areas and the understories of dense forests. The nest is constructed in a hidden place on the ground or low in a bush, where the 4 or 5 young will be fed caterpillars and other small invertebrates. Adults will also take nectar from blossoms and may visit your hummingbird feeder.
Orange-crowned Warblers are numerous and widespread on our islands. Look for them in areas where oceanspray, Pacific crabapple, and bitter cherry are backed by evergreen forests. Their greenish-yellow coloration blends in well with sunlit deciduous leaves.
These sprightly birds may leave as early as late June to travel upslope into the mountains. Unlike the hurried spring migration, fall movement can occur into October, with the peak being in late August. They winter from central California south to Guatemala.
Flora: Pacific Crabapple (Malus fusca)
This native fruit tree can grow as a cluster of shrubs or individual trees that can reach a height of 36 feet. Leaves are lance- or egg-shaped and measure two to three inches. The bark is reddish-brown or gray with scales and becomes fissured with age. Its branches have spurs that resemble thorns. Long-lived, some specimens have reached an age of 150 years.
Pacific crabapples host many pollinators in spring. Mourning Cloak butterflies use them as host plants and many bird species such as Orange-crowned and Wilson’s Warblers glean insects from the foliage. Robins, Purple Finches and Cedar Waxwings dine on the fruits.
Mammals are attracted to the crab apples, too. Deer browse the foliage and squirrels, chipmunks and deer mice vie for the fruit.
This tree is important for soil stabilization along ponds and watercourses. They do well in clay soils and wet areas. Look for them along the edges of moist forests, fringes of ponds, and the upper portions of ocean beaches.