Male Yellow-headed Blackbirds Research Articles

Responses of Nesting Yellow-Headed Blackbirds and Yellow Warblers to Wrens

Abstract We studied nest defense behavior of Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) and Yellow Warblers (Dendroica petechia) in response to two species of common nest destroyers. We presented freeze-dried models of Marsh Wrens (Cistothorus palustris) at Yellow-headed Blackbird nests and House Wrens (Troglodytes aedon) at Yellow Warbler nests during the incubation stage. We presented a Clay-colored Sparrow (Spizella pallida) as a control for both species. Male Yellow-headed Blackbirds responded more intensively to the Marsh Wren model than the control and female blackbirds responded intensively to both models but were more aggressive toward the Marsh Wren. Most Yellow Warblers did not respond to the House Wren model with their typical predator responses (e.g., alarm calls). Some female warblers were aggressive toward the wren model, whereas others sat in their nest. Sitting in the nest as a defense to deter nest destruction by House Wren needs further investigation. Differences in respons...

Sex-specific differences in site fidelity and the cost of dispersal in yellow-headed blackbirds

Male migratory birds tend to be more faithful than females to previous breeding sites, suggesting sex differences in costs or benefits of dispersal. In Illinois, greater site fidelity by male yellow-headed blackbirds (Xanthocephalus xanthocephalus) was associated with reduced reproductive success the following year for dispersers relative to non-dispersers. Dispersing females suffered no reduction in reproductive success the following year. Males that attracted few social mates, and thus had low reproductive success, were more likely to disperse, whereas females dispersed in response to low-patch reproductive success, regardless of their individual performance. Males that dispersed appeared to be successful acquiring territories because none was observed as a floater. The rate of dispersal by males in this low-density population was greater than in more dense populations where dispersing males may be less successful at acquiring territories. Despite success at obtaining territories, males that dispersed acquired territories on the periphery of wetlands where fewer females nested, resulting in lower reproductive success. In the second year after dispersing, however, males moved onto more central territories where they acquired larger harems. Thus, dispersal by males may be a long-term strategy requiring at least 2 years for benefits to be realized. Long-term success was enhanced because dispersing males moved to wetlands on which reproductive success was higher than on the wetlands they left. In addition to demonstrating that both individual and patch reproductive success affect dispersal decisions, these data indicate that when evaluating costs and benefits of dispersal, researchers should use a time frame beyond 1 year.

IMPACT OF BLACKBIRD DAMAGE TO SUNFLOWER: BIOENERGETIC AND ECONOMIC MODELS

We constructed bioenergetic and economic models to estimate the potential impact of Red-winged Blackbirds (Agelaius phoeniceus), Common Grackles (Quiscalus quiscula), and Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) on production yields of sunflower in the northern Great Plains of North America. The amount of sunflower consumed annually by males and females, after considering field metabolic rates, energy value and moisture content of achenes, and percentage of sunflower in diets was, respec- tively: Red-winged Blackbirds 277 g and 168 g; Common Grackles 267 g and 230 g; and Yellow-headed Blackbirds 248 g and 139 g. The per capita annual economic damage was: male Red-winged Blackbirds $0.09 (U.S. dollars), females $0.05; male Common Grackles $0.09, females $0.07; and male Yellow-headed Blackbirds $0.08, females $0.05. Annual loss was $5.4 + 1.3 X 106 for all three species in aggregate, with Red-winged Blackbirds accounting for 52% of the loss. Blackbird damage represented 1.7% of the dollar value of the 1999 sunflower harvest in the northern Great Plains. This loss would be inconsequential if damage were distributed evenly; however, bird damage is often localized around wetlands and can be economically debilitating to individual producers. Although our model was based on regional population estimates, it should perform well at local scales, provided that a local population can be defined, accurately estimated, and remains stable in size over the six-week length of the damage period. Because of the large numbers of blackbirds that congregate in the region during August and September prior to migration, sunflower pro- ducers should expect some crop losses. The solution to the conflict appears to be one that focuses not on eliminating all damage, but on preventing it from exceeding 5% per field.

Accepting unrelated broods helps replacement male yellow-headed blackbirds attract mates

Replacement male yellow-headed blackbirds (Xanthocephalus xanthocephalus) did not destroy broods sired by the previous territorial male and they showed no aggression toward females with unrelated broods. To test whether their tolerance of unrelated young was misdirected normal parental care, we removed males from experimental territories after primary nests were completed but before secondary nests were initiated. Replacement males fed young that they presumably had sired in secondary nests and ignored foster young in primary nests, whereas control males fed young in their primary nests. To identify potential benefits of accepting unrelated young, we analyzed patterns of within-season breeding dispersal and of female settlement on territories following nest losses to predators. Although some female yellowheads do renest on the same territory following nest failures, the number of nests initiated on territories after a predation event was significantly lower than the number initiated on territories without predation over the same period of time. This implies that late-settling females use the number of active or failed nests and/or the number of females on a territory when choosing where to breed. If replacement males that accepted unrelated offspring attract more new females in the remainder of the current breeding season than infanticidal males, then tolerance of unrelated young by replacement males may be adaptive in some polygynous birds.

Site fidelity and territorial movements of males in a rapidly declining population of yellow-headed blackbirds

We tested several hypotheses to explain low between-year territory fidelity in a breeding population of yellow-headed blackbirds (Xanthocephalus xanthocephalus). During a 5-year study the population of territorial males declined by two-thirds and some of the marshes that supported territories significantly deteriorated. Individual males held territories and bred for an average of 1.9 years. Of males that bred for at least 2 years, 30% skipped owning a territory in the study area during at least 1 year of their breeding lifetimes. Our information suggests that they may have bred outside of the area in those years. Of males with territories in two or more breeding seasons, 60% changed breeding marshes at least once. Males changed territories during 42.9% of between-year opportunities to do so. We found no support for the hypotheses that male yellow-headed blackbirds: (1) are more likely to move when territory density is low; (2) are likely to abandon territories that are deteriorating; or (3) change territories to improve their reproductive success. We suggest three non-mutually exclusive explanations for the yellow-headed blackbird's weak site fidelity: (1) it is a response to habitat deterioration and to other factors that may be causing the population's decline; (2) the males, being migratory, make fresh settlement decisions each year after they arrive on the breeding grounds in the general vicinity of their previous year's breeding; (3) yellow-headed blackbirds may have evolved in, and be adapted to, highly unstable habitats, moving frequently in response to changes in local breeding site conditions.

Genetic variation in male Yellow-headed Blackbirds from the northern Great Plains

Electrophoretic differences at 15 presumptive loci were used to assess allelic frequencies, heterozygosities, and polymorphism for male Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) collected in east-central Alberta, north-central North Dakota, and east-central South Dakota. Five loci were polymorphic and mean heterozygosities ranged from 0.119 to 0.133. Significant differences were detected among these geographic populations of Yellow-headed Blackbirds, primarily due to differences in the allelic frequencies of isocitrate dehydrogenase and glucose-6-phosphate dehydrogenase. Differences detected were not sufficient to uniquely identify the geographic origin of Yellow-headed Blackbrids.

Differential Growth Patterns of Nestling Brown-Headed Cowbirds and Yellow-Headed Blackbirds

-As nestlings, male Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) are significantly larger than female Yellow-headed Blackbirds in several measurements, and both male and female Yellow-headed Blackbirds are significantly larger than Brown-headed Cowbirds (Molothrus ater). We investigated the mechanisms by which female Yellow-headed Blackbirds are able to survive in nests with their larger siblings and how cowbirds are able to survive in the nests of hosts much larger than themselves. Growth was monitored of nestling Yellow-headed Blackbirds and Brown-headed Cowbirds, which were experimentally cross-fostered into Yellow-headed Blackbird nests, in Boulder County, Colorado during the 1986 breeding season. Measurements were recorded for weight, tarsometatarsus length, culmen length, gape width (width of bill at loral feathering), and length of ninth (outermost) primary. Nestling weight, tarsometatarsus length, and culmen length were larger in male than female Yellow-headed Blackbirds, and larger in both male and female Yellow-headed Blackbirds than cowbirds. Gape width differed significantly between male and female Yellowheaded Blackbirds throughout much of the nestling period; gape width in both were significantly wider than that of cowbirds. However, cowbirds had a significantly larger gape relative to their weight than did male Yellow-headed Blackbirds, and female Yellow-headed Blackbirds had a significantly larger gape relative to their weight than did males of the species. The relatively larger gape may enable females to compete with larger male siblings and enable cowbirds to compete with foster siblings much larger than themselves. Additionally, feather development was faster in female Yellow-headed Blackbirds than in males and was even more accelerated in cowbird nestlings. We used museum specimens of adults to calculate proportions of adult weight attained by nestlings. Cowbirds attained a greater proportion of their adult weight and adult ninth-primary length by fledging age than did Yellow-headed Blackbirds, and female Yellow-headed Blackbirds attained a greater proportion of their adult weight and adult ninth-primary length by fledging age than did their male siblings. Received 29 October 1990, accepted 10 January 1992. GROWTH rates vary greatly among animals and, although few grow at the highest potential rate (Needham 1964), they may grow at the maximum potential rate (Ricklefs 1969). Sibling competition may be a major component in the selection for rapid growth (Werschkul and Jackson 1979) and, in some species, may result in brood reduction (Bortolotti 1986). Brood reduction may occur through siblicide (Mock 1984) or asynchronous hatching (Lack 1954, Richter 1982, Mead and Morton 1985). Among sexually dimorphic, altricial birds that also hatch asynchronously, one might expect a high degree of sibling competition resulting in a biased sex ratio. While some investigators of sexually dimorphic birds have found skewed sex ratios of nestlings or fledglings (Howe 1977, Slagsvold 1 Present address: Department of Biology, Fort Lewis College, Durango, Colorado 81301, USA. et al. 1986, Teather and Weatherhead 1989), others have reported that sex ratios were not significantly skewed (Selander 1960, Fiala 1981, Bancroft 1983, Weatherhead 1983). Interestingly, in all the above-listed studies with skewed sex ratios, the sex ratios were female-biased. Explanations for female-biased sex ratios include: depending on hatching sequence, males suffer higher mortality during food shortages (Slagsvold et al. 1986, Teather and Weatherhead 1989); and males are more costly to raise (Howe 1977, Slagsvold et al. 1986). None of the above-listed studies, however, have shown how females may compete with their larger male siblings for food. Richter (1983) reported no significant bias in sex ratios for Yellow-headed Blackbirds (Xanthocephalus xanthocephalus), a sexually dimorphic, asynchronously hatching species. He demonstrated a significant difference between nestling growth rates of males and females, but suggested that there may be little disparity in

Results of dyeing male yellow-headed blackbirds solid black: implications for the arbitrary identity badge hypothesis

Territorial male yellow-headed blackbirds that were dyed solid black were similar to controls in their ability to attract mates. They also had no difficulty in defending their territories from floating males. The only remarkable effect of this dramatic color manipulation was that five of the 12 blackened males that regained a territory after being dyed also later took over the better quality territory of another male. Not one of the 11 control males that regained a territory succeeded in such an eviction. This surprising result is interpretable under the theory that conspicuous and distinctive coloration sometimes evolves as an arbitrary recognition badge by making good fighters more memorable to their opponents. With insight gained from these results, we modify and considerably expand the theoretical treatment of this Arbitrary Identity Badge Hypothesis. We also explain why our results for yellow-headed blackbrids should differ so dramatically from those for red-winged blackbirds where blackened males often lost their territories to floating males.

Adjustment of Parental Investment with Mate Quality by Male Yellow-Headed Blackbirds (Xanthocephalus xanthocephalus)

Abstract By removing young from the nests of competent females, I tested whether male Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) could assess the parental competence of mates and adjust their parental investment accordingly. The purpose of this experimental reduction was to equalize the number of young in nests of parentally competent and incompetent females in order to control for the effect of offspring number on parental investment by males. Males had a greater probability of feeding at nests of competent-reduced females and they fed at a higher rate than they did at nests of incompetent females. The latter broods were fed only when nests belonging to competent females were unavailable. Males adjust their parental investment with mate quality independent of the number of young in nests. To explain this preference, I constructed functions to relate the amount of paternal investment (i.e. male feeding rate) to the number of young fledged from nests and the fledging mass of young. The latter are two components of male reproductive success and, therefore, estimates of the "return" on a male's parental investment. Male feeding had no effect on the number of young fledged from starvation-reduced or experimental nests. However, the fledging mass of young increased more when males helped competent females than when incompetent females were helped. Thus male preference for helping competent females may result because the return per unit of their investment is greater at these nests.

An Experimental Study of Parental Investment and Polygyny in Male Blackbirds

Despite experimental reduction of the value of parental effort, male Brewer's blackbirds did not reallocate resources into mating effort; they did not attempt to mate polygynously. Although it was selectively advantageous for members of this population to do so, apparently no strong environmental potential for polygyny existed. Male yellow-headed blackbirds, when faced with a reduction of the marginal value of their 10 broods, reallocated investment toward their 20 broods but would not redirect feeding effort toward their 30 broods. Allocation of parental investment by these yellowheads was based on clutch size, nestling age and possible nestling sex.

Breeding Strategies of Male Yellow-Headed Blackbirds: Results of a Removal Experiment

Breeding Strategies of Male Yellow-Headed Blackbirds: Results of a Removal Experiment

Size and Mortality in Male Yellow-Headed Blackbirds

Journal Article Size and Mortality in Male Yellow-Headed Blackbirds Get access William A. Searcy William A. Searcy Department of Zoology, University of Washington, Seattle, Washington 98195 Present address: The Rockefeller University Field Research Center, Tyrrel Road, Millbrook, New York 12545. Search for other works by this author on: Oxford Academic Google Scholar The Condor, Volume 81, Issue 3, 1 August 1979, Pages 304–305, https://doi.org/10.2307/1367639 Published: 01 August 1979 Article history Accepted: 31 August 1978 Published: 01 August 1979