Cooperative breeding in the golden-cheeked warbler (Setophaga chrysoparia).
This federally endangered Neotropical migratory passerine breeds only in the juniper-oak (Juniperus ashei Quercus) woodlands of central Texas. Males begin arriving on breeding grounds in early March with females arriving a few days later (Ladd and Gass, 1999). Females begin construction of open-cup nests in mid-March and usually lay three or four eggs per clutch but occasionally five eggs (Pulich, 1976). Males do not assist in construction of nests (but see Lockwood, 1996; Graber et al., 2006), incubation, or brooding but feed females on the nest during incubation as well as nestlings and fledglings. Golden-cheeked warblers begin departing for wintering grounds as early as mid-June although some individuals may remain on the breeding grounds until late August (Ladd and Gass, 1999).
We observed two male golden-cheeked warblers feeding at the same nest in May 2009. We were conducting fieldwork associated with a long-term demographic study of marked individuals on Fort Hood Military Reservation (31[degrees]08,56.7"N, 97[degrees]46,02.6"W) in central Texas. For a detailed description of Fort Hood, see Eckrich et al. (1999). At least once every 5 days, we observed territorial males for >2 h to collect data about their behavior, patterns of movement, and reproductive activities. We used adult behavioral cues to locate nests and monitored them at least every other day. At each visit, we recorded date, time of visit, stage of the nest (building, laying, incubation, or nestling), and description of the activity of adult warblers at the nest. We used male behavioral cues (male singing softly and closely following a female collecting nesting material, male attempting to copulate with a female, male feeding an incubating female, and male feeding nestlings) to determine the social mate of the female. Once the young hatched, we increased the length and frequency of our monitoring visits to confirm the identity of the male feeding nestlings.
On 4 May, we observed a color-banded male (male 1) singing softly and closely following a color banded female as she collected nesting material. The female was completing construction of a new nest as her previous nesting attempt with male 1 was depredated earlier that morning. We located the nest on 5 May. We did not observe any other male golden-cheeked warblers attempting to follow or copulate with this female while she was constructing the nest or laying eggs. The female started laying eggs on 8 May and began incubating them on 10 May. The young hatched on 21 May. On 24 May, the female and male 1 fed nestlings at 0758 h (Central Standard Time). On 25 May, the female and a different color-banded male (male 2) from a neighboring territory fed nestlings at 0639 h. We observed male 2 feed nestlings again on 26 May at 0643 h. Male 1 and male 2 held adjacent territories in 2008 and 2009. We observed them fighting with each other and foraging within both of their territories throughout both breeding seasons. On 27 May, male 1 fed the nestlings at 0631 and 0642 h, the female fed them at 0637 h, and male 2 fed them at 0633 and 0642 h. Both color-banded males continued to assist the female in feeding the nestlings from 28 May-29 May. Both males often sang as they approached the nest to feed the nestlings, but we never observed one of them attempt to chase or fight with the other one at it, even though they were both at the nest feeding nestlings at the same time on 27 May. On 30 May, we observed both males together, ca. 250 m from the nest, singing and collecting food. They did not display any defensive behavior toward each other at this time. The nestlings fledged on 1 June. Male 1 fed one fledgling ca. 50 m from the nest, and male 2 fed another fledgling ca. 25 m from the nest. We were not able to locate the female feeding fledglings.
While we did not observe this female attempt to copulate with either male and paternity of the brood is unknown, we hypothesize that this case of cooperative breeding resulted from an extrapair-copulation between the female and male 2 during her fertile period. Female golden-cheeked warblers solicit extrapair-copulations from males that are not their social mate (R. G. Peak, pens, observ.). Extrapair-patemity ranging from 13-47% has been confirmed in six species of warblers (Perreault et al., 1997; Stutchbury et al., 1997; Yezerinac and Weatherhead, 1997; Chuang et al., 1999; Thusius et al., 2001; Byers et al., 2004), suggesting that extrapair-fertilizations can be an important mating tactic for this group.
Researchers have hypothesized that frequency of extrapair-fertilizations is influenced by breeding synchrony (Birkhead and Biggins, 1987; Stutchbury and Morton, 1995), breeding density (Birkhead, 1978; Gladstone, 1979; Birkhead et al., 1987; Hatchwell, 1988), and an interaction between these factors (Chuang et al., 1999, Thusius et al., 2001). Other researchers have hypothesized that level of male parental care (Ketterson and Nolan, 1994; Gowaty, 1996), rate of adult mortality (Mauck et al., 1999), and genetic variability among males in a population (Westneat et al., 1990; Brown, 1997) influence frequency of extrapair-fertilizations among species. We do not have genetic data to determine parentage of offspring or frequency of extrapair-fertilizations in this population and cannot test if these hypotheses explain why individuals in the population we studied would adopt an extrapair-mating strategy. However, male golden-cheeked warblers are frequently observed guarding their mate during construction of nests and egg-laying, but, once incubation begins, the males are observed in the territories of other pairs closely following and attempting to copulate with another female as she constructs a nest (R. G. Peak, pens, observ.), all behaviors that suggest extrapair-fertilizations occur in this species.
Our observations demonstrate that, in addition to polygyny (Peak et al., 2010), cooperative breeding is an alternative mating strategy for golden-cheeked warblers. We hypothesize that male 1 and male 2 provided parental care to this brood because both attempted to copulate with the female during her fertile period. During 20032011 breeding seasons, feeding behavior of adults to nestlings has been observed for [greater than or equal to] 25 min every 1-2 days for 409 nests, with no prior observations of cooperative breeding. Hence, it appears that cooperative breeding does not occur frequently in golden-cheeked warblers. However, we concur with Tarof and Stutchbury (1996) that cooperative breeding in species of warblers is likely more prevalent than currently has been documented. We recommend future studies of the breeding ecology of golden-cheeked warblers should include genetic studies to confirm the existence of extrapair-fertilizations in this species and, if it does occur, the potential selective pressures that influence the use of this mating strategy.
We thank numerous seasonal biologists for assistance in the field. This project was sponsored in part by the Department of the Army with The Nature Conservancy through Cooperative Agreement DPW-ENV-02-A-0001.
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Submitted 6 January 2012. Accepted 3 February 2014.
Associate Editor was Mariis R. Douglas.
REBECCA G. PEAK * AND SARAH W. KENDRICK
United States Army Garrison-Fort Hood, Directorate of Public Works, 4612 Engineer Drive, Room 76, Fort Hood, I X 76544
Present address of SWK: Department of Fisheries and Wildlife Sciences, 302 Anheuser-Busch Natural Resources Building, University of
Missouri, Columbia, MO 65211-7240
* Correspondent: email@example.com
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|Author:||Peak, Rebecca G.; Kendrick, Sarah W.|
|Date:||Dec 1, 2013|
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