Yellow-headed Blackbird (Xanthocephalus xanthocephalus)

I studied the effects of food availability, habitat quality, and timing of breeding on egg production in yellow-headed blackbirds (Xanthocephalus xanthocephalus). Food availability was experimentally manipulated by providing females on six wetlands with supplemental food; six additional wetlands served as unsupplemented controls. Mean nest initiation dates varied by up to 6 d among wetlands, and supplementally fed blackbirds initiated nests 2 d earlier than controls, on average (although this latter difference was not quite significant; P = 0.07). Clutch size declined with laying date, but was unaffected by wetland location, food supplementation, or interactions between these two factors and laying date. Although egg size did not vary among wetlands or in relation to supplemental feeding, egg composition varied with both of these factors. All egg components except wet and dry shell and dry albumen varied among wetlands, whereas total water, wet yolk, and lean yolk were the only components that varied with food supplementation. Large blackbird eggs contained proportionately more water and albumen, but proportionately less yolk and shell. These patterns were somewhat compensatory, such that proportional protein and energy content did not vary with egg size; however, large eggs contained proportionately less fat than did small eggs. Proportional egg composition varied among wetlands (yolk and energy content), but was not affected by supplemental feeding. In general, egg production by yellow-headed blackbirds was not greatly affected by food availability. This may have been due to any of the following four factors: (1) inaccessibility of food supplements owing to competition between male and female blackbirds, (2) insufficient time for females to respond to food supplements, owing to rapid settlement and nest initiation, (3) a nutritionally inappropriate food supplement (i.e., protein availability may not have been enhanced among fed birds), or (4) superabundance of natural foods such that food availability was not limiting egg production.

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

Canadian Journal of Zoology ◽

10.1139/z92-305 ◽

1992 ◽

Vol 70 (11) ◽

pp. 2280-2282 ◽

Cited By ~ 2

Author(s):

Daniel J. Twedt ◽

William J. Bleier ◽

George M. Linz

Keyword(s):

Great Plains ◽

Geographic Origin ◽

Northern Great Plains ◽

North Central ◽

East Central ◽

Allelic Frequencies ◽

Xanthocephalus Xanthocephalus ◽

Geographic Populations ◽

Glucose 6 Phosphate Dehydrogenase ◽

Central South

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.

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GENETIC SOURCES OF RESISTANCE TO BLACKBIRD PREDATION IN SUNFLOWER

Canadian Journal of Plant Science ◽

10.4141/cjps86-003 ◽

1986 ◽

Vol 66 (1) ◽

pp. 19-23 ◽

Cited By ~ 4

Author(s):

DAN E. PARFITT ◽

GREGORY J. FOX

Keyword(s):

Agelaius Phoeniceus ◽

Narrow Sense ◽

Sources Of Resistance ◽

Bird Predation ◽

Narrow Sense Heritability ◽

The Third ◽

Naturally Occurring ◽

Xanthocephalus Xanthocephalus ◽

Sib Families ◽

Highly Correlated

Fifty-one sunflower (Helianthus annuus L.) inbreds were grown at three environments (locations) in North Dakota. Inbreds at two locations were subjected to naturally occurring bird predation by redwinged blackbirds (Agelaius phoeniceus L.) and yellowheaded blackbirds (Xanthocephalus xanthocephalus Bonaparte). The third sunflower plot was surrounded by a cage into which redwinged blackbirds were introduced. Bird damage was estimated as percent achenes removed from individual sunflower heads. Significant differences among environments were observed (P < 0.01). However, genotype performance among environments was highly correlated (P < 0.01). Half sib progeny from 36 of these inbreds were grown along with their maternal inbred parents to estimate narrow sense heritability (h2NS) of resistance to bird predation. Estimates of h2NS obtained by parent offspring regression and by covariance among half-sib families were h2NS = 0.69 and h2NS = 0.66, respectively. These estimates indicate a 67% level of heritability for resistance to bird predation, and suggest that it should be possible to develop sunflower lines with improved resistance.Key words: Sunflower, bird feeding, redwinged blackbird, yellowheaded blackbird

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