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Return of the Least Bell's Vireo

Julian Wood

I am crouched low and hiding, surrounded by giant mugwort plants, in the largest riparian restoration plot in the San Joaquin Valley National Wildlife Refuge. I'm on the verge of discovering the nest of an endangered bird that, at its low point in the 1980s, was reduced to 300 pairs in Southern California.

I see something moving and instantly freeze. It is the male Least Bell's Vireo staring straight back at me as he makes his way along the outer branch of an arroyo willow. My heart stops when I see the nest! I have just found the first confirmed nest of a Least Bell's Vireo after decades of this bird's absence from the entire Central Valley!

The nest is slung in the outer fork of the lowest arroyo willow branch, partially concealed by the dense mugwort. Although I am close by, the fearless male is not disturbed by my presence. He proceeds to casually feed his young and then sit low on the nest. Then, he begins to sing right from the nest, a trait common to this vociferous vireo. Such broadcast of the nest location is one of the reasons this species is so heavily parasitized by Brown-headed Cowbirds, who lay their eggs in other birds' nests.

As I kneel uncomfortably, still frozen in place, the female appears. She relieves the male from his paternal duties and proceeds to feed her chicks. Eventually, after both my legs have fallen asleep, the parents leave, and I am able to check the nest contents: two perfect eggs and two pink and naked young just hours old. No Brown-headed Cowbirds here!

Could this one nest herald the return of the Least Bell's Vireo to the Central Valley?

From all the vigorous plant life surrounding me, it is difficult to imagine the rows of crops that grew here just five years ago. The mixed willows, cottonwoods, and a native shrubby understory are a perfect match for the habitat requirements of Least Bell's Vireo and other riparian-loving birds. This prime habitat is the product of an ambitious CALFED-funded restoration project involving USFWS, PRBO, and River Partners (riparian restoration specialists). River Partners' novel practice of planting a dense native understory follows recommendations found in the Riparian Bird Conservation Plan (Produced in 1999 with California Partners in Flight) and drawn from ongoing monitoring by PRBO and our many partners.

We have much more to learn to ensure that these restored habitats support viable bird populations, adapting our recommendations as the sites continue to mature and numbers and types of birds using them change.

What does the future hold? Perhaps foretelling the vireo's return, the Yellow Warbler, another species long absent from the San Joaquin Valley, is breeding on the refuge. From the first pair found in 2002 to over 13 pairs today, Yellow Warbler has recolonized a portion of its former breeding ground.

Improving habitat conditions on the refuge and nearby private lands (thanks to state and federal programs with the landowners) may support more of these vireos' and warblers' progeny returning to nest in future years. I already anticipate the return of other species exiled from the riverside forests, such as Yellow-billed Cuckoo and Warbling Vireo.

With all this hard work and good science from a variety of partners, the Central Valley's wildlife and the habitat that supports it are coming back to life!

And so are my legs as I make my way out of the field grinning from ear to ear.