Lucas J. Redmond

Reproductive correlates of spring arrival date in the Eastern Kingbird Tyrannus tyrannus

Harsh weather in spring presents energetic challenges to birds during migration and upon reaching the breeding grounds, and yet, birds often arrive well before breeding begins. We studied a population of Eastern Kingbirds in eastern Oregon from 2004 through 2007. Early arriving kingbirds faced the poorest weather conditions, and therefore we predicted that benefits of early arrival must exist to balance the presumed costs. Early-arriving kingbirds were more likely to both acquire a high-quality territory and to replace nests after failure. Early-arriving birds also bred early, and early breeding led to larger clutches and greater production of young. Early-arriving males also sired more extra-pair young than later arrivers. Our data suggest that arrival date is in part influenced by individual quality, and that arrival date has reproductive consequences, with the primary benefits of early arrival being the acquisition of a high-quality territory, early breeding, and increased probability of replacing failed initial nests.

Parental Investment Theory and Nest Defense by Eastern Kingbirds

Abstract Nest defense represents a parental strategy to maximize fitness by enhancing prospects of offspring survival. We used a taxidermic mount of a nest predator to measure nest defense of Eastern Kingbirds (Tyrannus tyrannus) at Malheur National Wildlife Refuge in southeastern Oregon in 2003 and 2004 to test the hypotheses that intensity of nest defense (1) was individually repeatable, (2) differed between males and females, and (3) predicted nest success. We also predicted that (4) intensity of defense would increase with age and number of young, but decline over the breeding season. Intensity of nest defense was significantly repeatable for male kingbirds. Male response was twice as strong as female response during incubation and the nestling period, but nest success was independent of defense scores of males and females. Simple paired comparisons suggested female responses did not change between incubation and the nestling period, whereas males tended to defend nestlings more vigorously than eggs. Multivariate analyses demonstrated strong individual differences were the main source of variation in nest defense. Intensity of nest defense by males and females increased with age of young, declined seasonally, but was not related to number of young. Kingbird nest defense is a repeatable behavior that differs between males and females and, as predicted by parental investment theory, nests of the greatest value (older young and earlier broods) were defended most aggressively.

NEST REUSE BY EASTERN KINGBIRDS: ADAPTIVE BEHAVIOR OR ECOLOGICAL CONSTRAINT?

Abstract The reuse of old nests by open-cup nesting passerines is a seemingly rare but potentially adaptive behavior if, as a consequence, females begin to breed earlier, lay larger clutches, or fledge more young. We report an unusually high rate of nest reuse (~10% of 341 nests) for Eastern Kingbirds (Tyrannus tyrannus) breeding at Malheur National Wildlife Refuge, Oregon. We found no difference in availability of nesting habitat or food abundance in territories in which nests were and were not reused. We also found no support for the hypotheses that kingbirds benefited from nest reuse by breeding earlier, laying larger clutches, or fledging more young, and, contrary to expectations, females that reused nests laid significantly smaller eggs than females who built their own nests. Nest reuse was independent of age: a roughly equal number of females for which we had multiple years of data both reused nests and built new nests, but at different points in their lives. Competition for nest sites seems high at Malheur National Wildlife Refuge because many open-cup nesting species utilize similar nest sites in the limited zone of riparian vegetation. A shortage of high-quality nest sites, coupled with interspecific competition, may underlie the high frequency of nest reuse in this kingbird population.

Maternal characteristics and the production and recruitment of sons in the eastern kingbird (Tyrannus tyrannus)

Sex allocation theory predicts that if variance in reproductive success differs between the sexes, females who are able to produce high-quality young should bias offspring sex ratio towards the sex with the higher potential reproductive success. We tested the hypothesis that high-quality (i.e., heavy) female eastern kingbirds (Tyrannus tyrannus) that bred early in the breeding season would produce male-biased clutches. A significant opportunity for sexual selection also exists in this socially monogamous but cryptically polygamous species, and we predicted that successful extra-pair (EP) sires would be associated with an excess of male offspring. Although population brood sex ratio did not differ from parity, it increased significantly with female body mass and declined with female breeding date, but was independent of the morphology and display (song) behavior (correlates of reproductive success) of social males and EP sires. Male offspring were significantly heavier than female offspring at fledging. Moreover, the probability that male offspring were resighted in subsequent years declined with breeding date, and was greater in replacement clutches, but lower when clutch size was large. Probability of resighting female offspring varied annually, but was independent of all other variables. Given that variance in reproductive success of male kingbirds is much greater than that of females, and that male offspring are more expensive to produce and have a higher probability of recruitment if fledged early in the season, our results support predictions of sex allocation theory: high-quality (heavy) females breeding when conditions were optimal for male recruitment produced an excess of sons.

Multistate Mark-Recapture Analysis Reveals no Effect of Blood Sampling on Survival and Recapture of Eastern Kingbirds (Tyrannus tyrannus)

ABSTRACT. The experimentally supported and prevailing opinion is that blood sampling has few to no long-term effects on survival of birds when conducted properly, and blood sampling has become a vital addition to the toolbox of many ornithologists. However, many of the studies that concluded that blood sampling had negligible effects on birds used approaches that did not account for temporary emigration and probability of capture. To date, the only study to have done so found that blood sampling had a strong negative effect on survival. We conducted a mark-recapture analysis of 8 years of banding and bleeding data on Eastern Kingbirds (Tyrannus tyrannus) to determine whether survival was negatively influenced by blood sampling. Our analyses adjusted for temporary emigration and probability of recapture and accounted for (1) transitions between the bled and the nonbled state and (2) a change in protocol roughly midway through the study that resulted in a change from single to often multiple (and larger) draws of blood per year from single individuals. We found that survival rates of nonbled (0.61) and bled (0.67) males were statistically indistinguishable and that bled females had a higher probability of survival than nonbled females (0.68 and 0.58, respectively). The change to larger and more frequent blood samples was also not associated with a change in survival. Our data show that when accepted protocols were followed, blood sampling had no detectable influence on the survival of adult Eastern Kingbirds. Whether this applies generally awaits analyses using similarly rigorous methods on other species.

Unusual Barn Swallow Nest Placement in Southeastern Oregon

Abstract Barn Swallows (Hirundo rustica) historically nested along cliffs, in caves, and in other natural situations. Currently, nearly all reported nests of this species are on walls and beams of bridges, buildings, and other human-derived structures. Both natural and man-made nest sites typically share one thing in common: a horizontal surface for nest attachment. We describe a Barn Swallow nest that was constructed on a branch overhanging a river in southeastern Oregon. This is the first documented occurrence of this behavior by Barn Swallows and we believe it to be the result of high competition for a limited number of suitable nest sites in the study area.

Paternal behaviour in a socially monogamous but sexually promiscuous passerine bird

We documented parental behaviour and paternity of eastern kingbirds (Tyrannus tyrannus) to test the predictions that paternal care would decline with increasing loss of paternity, increasing nesting density (a proxy for probability of paternity loss), male quality, and number of fertile females available in the population. Extra-pair young were found in 58% of 45 nests for which behaviour was recorded and a higher proportion of young were extra-pair as nesting density increased. Male feeding rate declined with increasing nesting density and male quality, but neither feeding rate nor a composite measure of paternal behaviour varied with number of fertile females or paternity. Although alternative explanations exist, one interpretation of the reduced paternal care at high nesting density was that it was a response to perceived threats of paternity loss. The ultimate basis for the lower paternal effort of higher quality males is unclear but we discuss several possible explanations.