Birdwatching in Santa Barbara: The Miracle of Migration

Warmer, longer days stir up the sap to flow through the sycamores of the creek and cause the leaves to unfurl. The blood of the birds is also quickening and the excitement of spring is revealed in songs and showy colors. The migration miracle is now in full swing: at one point the wintering white-crowned sparrows sing their happy, windy song, then suddenly they’ve been supplanted by impossibly bright hooded orioles.

Migration has always fascinated – and baffled – humans, perhaps because of the suddenness of departures and arrivals. It is only for a hundred years that we begin to understand the mechanisms of migration.

Rufous hummingbirds stop to refuel before continuing north. | Credit: Hugh Ranson

Theories have abounded over the centuries about the movements of birds. Aristotle believed that swallows and other summer visitors hibernated – that they flew into the crevices of trees to spend the winter dormant. He also speculated that some species morphed into others – in the fall, European redstarts morphed into European robins for the duration of winter. Others have speculated that swallows dive to the bottom of ponds to spend the winter hibernating in the mud. Perhaps one of the more outlandish ideas, but one that had been around for a while, was that birds were flying to the moon. You can see how this idea may have come about: on autumn nights it is possible to see ghost birds on the face of the moon.

Late March to late April is a special time in the birdwatcher’s calendar, as birds arriving from Mexico and further south are greeted by our winter visitors, who wait for the right time to fly north. Some birds, like the Rufous Hummingbird, won’t stop for long, refueling for a day or two before continuing north. Perhaps the most showy of all our summer residents is the male hooded oriole. If you have palm trees in your neighborhood, you probably have orioles because they prefer to build their hanging nests under palm fronds. The females make holes in the fronds and sew the nest with plant fibers.

The female hooded oriole is yellow and green and blends in well with its surroundings. It is the male who is the highlight of the show. It is black above and on the throat, but its head and underparts are bright yellow. Even with its bright colors, the male can be difficult to locate, as orioles are shy birds. Knowing the song – a raspy chatter interspersed with softer notes – or especially the call notes, can help you focus on the bird. A typical call is a soft, upward inflected “wheep” that carries over long distances. This is often the first clue that hooded orioles have returned to your neighborhood.

Many of our summer birds tend to congregate along streams. The chirping vireos are already here singing their beautiful songs, while the quiet Pacific slope flycatcher marks its territory with a simple, repetitive song. Black-capped Grosbeaks have robin-like chirps, while Yellow Warblers sing with soft, clear notes.

Alongside these new arrivals, the birds prepare for departure. This is the only time of year when the chatter of the cloaked oriole mixes with the faint whistles of the white-crowned sparrows. These sparrows sing all winter, but it is only in spring that the mornings come alive with their songs. As April stretches on, you notice that there are fewer and fewer of them in the song, until one morning they are gone.

The white-crowned sparrows will be leaving soon. | Credit: Hugh Ranson

The hidden dangers of the night must surely terrify the perched birds, but the urge to migrate overcomes these fears, and in the night they must fly. In recent years, the understanding of the mechanisms of migration has become clearer. Birds use many cues to travel the immense distances that many of them travel. They include the position of the sun, the patterns of the stars, the smells of familiar places, and the earth’s magnetic field. It is this latter mechanism that has generated some of the most fascinating research in recent years.

It seems that birds are able to “see” the Earth’s magnetic field lines. This all has to do with quantum spin dynamics with radical pairs forming in the retinas of birds as they migrate – understanding how this works is beyond the scope of this article (and my understanding!). This mechanism allows birds to travel thousands of miles at night to find the same tree in which they nested the previous summer. For juveniles, their first journey south is fraught with difficulty, and indeed only 30% survive to reach their ancestral wintering grounds. For those who complete the journey successfully, however, the correct route is etched in their memory.

Much remains to be discovered about the mechanisms underlying bird migrations. But for most of us, it is enough to marvel at this extraordinary, age-old event. And, of course, that first dazzling hooded oriole of spring.

Pacific slope flycatchers are common summer birds along our streams. | Credit: Hugh Ranson

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