Focus On...the Indigo and Lazuli Buntings
Of the new breeding species gradually infiltrating San Diego County, which could be more welcome than the Indigo Bunting? A bird so brilliant it not only dazzles but seduces the eye with its subtle shifting gloss. Since the 1940s the Indigo Bunting has been pioneering west out of its core range in the eastern United States, and these pioneers are becoming ever more frequent in San Diego County. From two sightings in spring and summer 1997, one in 1998, and none in 1999, we went to seven in 2000, 11 in 2001, and at least six already in 2002. The Indigo Bunting's arrival brings new prominence to an often neglected identification problem, distinguishing the brown female Indigo from the female Lazuli Bunting. And frequent hybridization between these two closely related species threatens to confound the problem even further, as Jim Wilson, Phil Nelson, and I found at Jacumba in 2000. The Lazuli Bunting was among the many spring migrants that were unusually prominent in spring 2002, perhaps compelled to seek irrigated developed areas because of drought-induced lack of food in natural habitats. Gjon Hazard reported 50 in the Borrego Valley on 20 April, and Bert McIntosh noted up to a dozen in a day at his home in Poway. Thus the Indigo and Lazuli Buntings seemed a logical selection to "focus on" in this final issue of Wrenderings.
When we address the identification of the female and immature Indigo and Lazuli Buntings, these birds take us to a frontier of ornithology, the details of molt. The buntings have taken a leading role in compelling ornithologists to look more closely at just which feathers the birds are replacing when, and how the process of molt, a big demand on the physiology of a small bird, fits with the other demands of migration and breeding.
By definition, the coat of feathers that a bird wears when it leaves the nest is called the juvenile or juvenal plumage. In both the Indigo and Lazuli the juvenile plumage is streaked below, heavily in the Indigo, lightly in the Lazuli. Hybrid juveniles have noticeably heavier streaking than the Lazuli, as Mary Beth Stowe and I observed near the Warner Springs fire station (F19) on 28 June 2001. Unfortunately, no field guide illustrates the juvenile buntings, not even David Sibley's guide, which portrays many more juveniles than the others. In some Lazuli Buntings and all Indigo Buntings the body or contour feathers of the juvenile plumage are replaced by the next plumage beginning just a few days after fledging, while the juvenile flight feathers are still growing. This "supplemental" plumage, which resembles the adult female's, takes the birds through fall migration--at least the first leg of it, until they have left southern California. This scenario presented in the literature, however, may not be the complete story. In 1988 on 4 September, a date when the birds should be migrating and out of juvenile plumage, Roger Higson and I collected at Arsenic Spring, near the current De Anza Springs nudist camp (T28), a young Lazuli Bunting still with streaks and the lacy plumage texture characteristic of juveniles. In any case, at this stage, the Lazuli is distinguishable by its distinct if subtle buff breast band, the Indigo by its lighter throat, dull brown lightly streaked breast, and rich warm brown upperparts. Both species have wing bars, but they are deep buffy brown, like the back, in the Indigo, contrastingly paler buff to whitish in the Lazuli.
Bruce E. Young, in his 1991 paper published in the Condor (93:236-250), reported that Lazuli Buntings stop to engage in their next molt at an intermediate spot on their fall migration. These pauses take place in southeastern Arizona, southwestern New Mexico, northern Sonora, or southern Baja California Sur. But the reported story may be incomplete here too. Sanford Wilbur, in his 1987 book, Birds of Baja California, wrote "there are no recent winter records" of the Lazuli Bunting in Baja California's cape district, influencing Young's analysis. In fact, there are numerous winter observations in this area, as I reported in the recent synthesis of Baja California birds edited by Dick Erickson and Steve Howell and published as Monographs in Field Ornithology number 3 by the American Birding Association. Thus the habits of the Lazuli Bunting may be more conventional, many birds simply molting when they arrive in their winter range, like the Willow Flycatcher, Black-headed Grosbeak, and others.
This molt, the "prebasic" molt, takes the birds another step closer to their breeding plumage, especially in the Lazuli. In the Lazuli, the male's first-winter plumage is like the summer plumage but the wingbars may be tinged buff and all the blue feathers have rich buff tips, giving an exquisitely beautiful effect--as I saw in southern Baja California. It's a shame we never have the opportunity to see this plumage in San Diego. The male Indigo in its first winter also has the plumage variably tipped and blotched with brown. The first-winter female Lazuli resembles the adult but has little or no blue on the rump and edges of the flight feathers.
Before the birds depart their winter range in the spring, they molt yet again. In the Lazuli, though, this spring "prealternate" molt is minor, confined to the feathers of the face. The conversion of the male from its muted winter plumage to its radiant breeding plumage is accomplished almost entirely by the buff tips' being worn off. The Indigo molts more extensively than the Lazuli at this stage, more brown feathers being replaced by blue. Some first-year male Indigos are extensively white on the belly and undertail coverts--thus resembling possible hybrids with the Lazuli.
In spite of all this molting, by spring the feathers that are so helpful in identifying the females, the secondary coverts, which bear the wingbars, are getting worn. By midsummer, the inconspicuous brown edges of the female Indigo may be completely gone, and the whitish wingbars of the female Lazuli, especially the narrower lower one, are not far behind. The rich brown of the female Indigo's upperparts gets bleached and drab. The Lazuli retains its buff breast band, the Indigo its diffuse breast streaks, but seeing these requires a good view. Just as with the Red-winged and Tricolored Blackbirds, the later in the summer, the more difficult the birds are to tell apart.
And, as we have found, the identity of a bunting is no guide to the identity of its mate. As the Indigo spreads into the West, the scattered pioneers are much more likely to find a Lazuli for a mate than another Indigo. Experiments show that in captivity females prefer their own kind, but on the frontier the birds may not have the luxury of discrimination. Males, as usual, take anything they can get. I outlined the story of all the apparent mixed pairs in the account of the Indigo. An unambiguous pure pair of the Indigo in San Diego County was found for the first time this year. After finding the nest of a mixed pair near Scissors Crossing, Joe Barth found a pair of pure Indigos, the male a blotchy blue-and white first-year bird, the female building a nest. Though this nest was abandoned shortly after being built, the Indigo's invasion is shifting into an even higher gear.
Allow me to finish this article focusing on the buntings by offering drafts of the accounts of each of them I have written for the atlas. As always, I welcome your comments. Happy bunting!