Successful interbreeding of two Vireo species in California leads to keen interest in the hatchlings

Melissa Blundell, graduate student at UC Davis.

Barbara Kus Kus is a well known expert on California's Vireos.

A male Least Bell’s Vireo (left) building a nest in May 2010 with a female White-eyed Vireo (right) at the San Luis Rey River in California.Photo: Lisa D. Allen

Least Bell's Vireo

A male Least Bell’s Vireo (Vireo bellii pusillus) in May 2010 wove a nest in the branch of an arroyo willow along the San Luis Rey River in Oceanside, California. But he didn’t build it for a female of his own species.

A male Least Bell’s Vireo (left) building a nest in May 2010 with a female White-eyed Vireo (right) at the San Luis Rey River in California.Photo: Lisa D. Allen

By Rex Graham

His mate was a female White-eyed Vireo (V. griseus). The female soon laid four eggs, and the pair successfully raised and fledged four nestlings. It was the first documented case of interspecific breeding involving the two Vireo species.

Melissa Blundell, a graduate student in animal behavior at UC Davis, and Barbara Kus, a distinguished research ecologist with the U.S. Geological Survey (USGS), reported in the September issue of the Wilson Journal of Ornithology the first interspecific mating of the two vireo species.

Blundell and Kus mist-netted the female White-eyed Vireo, but not the male Least Bell’s Vireo in order to minimize disturbance at the nest.

Melissa Blundell, graduate student at UC Davis,

They also examined the four chicks and collected DNA samples from them and the mother. “We collected a pin feather sample from each nestling and a blood sample from the female via a toenail clip,” they wrote in the Wilson Journal. “This genetic material is currently being analyzed for further evidence of this interspecific breeding occurrence.”

The nest was empty by June 14. Two fledglings were heard calling nearby. Blundell and Kus visited the nesting area three more times and searched unsuccessfully for a second nesting attempt.

The female White-eyed Vireo vanished, but Blundell observed one of the banded fledglings with the male Least Bell’s Vireo on June 27. The fledgling resembled a Least Bell’s Vireo fledgling in appearance with a white underbelly, gray crown, back and primaries, and black eyes.

Blundell and Kus hope to observe members of the unusual Vireo family in the future.

Kus is a well known Vireo expert who knows their breeding habits as well as anybody. After she graduated with a Ph.D. from UC Davis in 1985, she began working for the USGS’s Western Ecological Research Center, and has also been associated with the Department of Biology at San Diego State University. She has published more than 25 scientific papers on Neotropical migratory birds in restored woodlands, and she has developed a special expertise on the Least Bell’s Vireo.

Barbara Kus Kus is a well known expert on California's Vireos.

Kus and Blundell are now members of a small group of people who have personally witnessed an interspecific Vireo mating. One of the first such recorded observations was made on May 26, 1958, by Doris Hauser. She saw a male Yellow-throated Vireo (V. flavifrons) display a few inches from its nest in a post oak in her front yard at 309 Sylvan Road in Fayetteville, N.C. Hauser watched the male mate twice there with a wing-fluttering female Solitary Vireo (V. solitaries).

Other hybridizations among Vireo species have been reported*:

V. altiloquus and V. olivaceus
V. cassinii and V. plumbeus
V. flavifrons and V, solitaries
V. olivaceus and V. altiloquus
V. olivaceus and V. philadelphicus
V. philadelphicus and V. olivaceus
V. plumbeus and V. cassinii
V. solitaries and V. cassinii
(*Source: bird-hybrids.com)

Actually, hybridization in birds is well known. About one in 10 species is known to hybridize: as many as 895 species of birds are known to have bred in nature with another species and produced hybrid offspring, out of a world total of 9,672 species, according to Princeton University’s Peter and Rosemary Grant, legendary evolutionary biologists who studied the finches of the Galapagos island of Daphne Major for four decades.

Order	Species	Species hybridizing	Species hybridizing
	number	number	percent
Struthioniformes Photo: Lip Kee Yap	10	0	0
Tinamiformes Photo.Marcos Massarioli	47	0	0
Craciformes Photo: Dario Sanches	69	2	2.9
Galliformes Photo: JJ Harrison	214	46	21.5
Anseriformes Photo: Kitkatcrazy	161	67	41.6
Turniciformes	17	0	0
Piciformes Photo: Alan Vernon	355	48	13.5
Galbuliformes Photo: Brian Gratwicke	51	2	3.9
Bucerotiformes Photo: Lip Kee Yap	56	0	0
Upupiformes Photo: Alan Manson	10	0	0
Trogoniformes Photo: Matt MacGillivray	39	0	0
Coraciformes Photo: Piotr Kuczynski	152	8	5.3
Coliiformes Photo: Alois Staudacher	6	2	16.7
Cuculiformes Photo. Mark A. Wilson	143	4	2.8
Psittaciformes Photo. Louise Docker.	358	27	7.5
Apodiformes Photo. Jakub Stanco	103	0	0
Trochiliformes Photo. Michelle aka Mitternacht90	319	61	19.1
Musophagiformes Photoz; Chrumps	23	0	0
Strigiformes Photo: Dori	291	2	0.7
Columbiformes Photo. 4028mdk09	313	10	3.2
Gruiformes Photo. Marek Velechovsky	196	17	8.7
Ciconiiformes Photo. Dick Daniels	1,027	139	13.5
Passeriformes Photo. Donna Dewhurst	5,712	460	8.0
TOTAL	9,672	895	9.2

The Grants reported in Science magazine that 460 of the 5,712 species of Passeriformes have hybridized, but the true global incidence of bird hybridization is likely to be higher than 10 percent.

The Grants banded almost every bird on Daphne Major for years and documented the fitness of hybrid birds, finding that in many combinations of species, hybrid offspring survived better than their related-species contemporaries. They speculated that hybrids may be better able to deal with the exigencies of the environment better than parental species phenotypes.

“Hybrids, as well as surviving well, breed well; they are fertile as well as viable,” the Grants reported. However, genetic incompatibilities between hybridizing species sometimes appear in subsequent generations.

Least Bell's Vireo

The Least Bell’s Vireo it is an endangered species that breeds from northern Baja California, Mexico north to San Diego County in Southern California along the San Luis Rey and Santa Margarita rivers.

The White-eyed Vireo breeds in eastern North American from Florida and Massachusetts on the east through Illinois on the west. There have been only 67 confirmed sightings of a White-eyed Vireo in California between 1969 and 2009, according to Blundell and Kus.

Such small populations of a Vireo species such as the Least Bell’s might be expected to result in “inbreeding depression,” the reduced fitness that results when more deleterious traits become manifest. Kus and Blundell’s hybrid Vireos could provide insight into what the future may hold for the Least Bell’s.

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Posted by Rex Graham on Sep 5 2011. Filed under Endangered Birds, Research, United States. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry