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Robert E Ricklefs - One of the best experts on this subject based on the ideXlab platform.
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The effects of brood size on growth and steroid hormone concentrations in nestling eastern Bluebirds (Sialia sialis)
General and Comparative Endocrinology, 2011Co-Authors: Corinne P. Kozlowski, Robert E RicklefsAbstract:Abstract Birds in multi-nestling broods often experience reduced growth and elevated nutritional and social stress as a result of competition for parental resources. While responses are often species-specific, experimentally increasing brood size has been shown to decrease growth and increase production of both testosterone and corticosterone in nestling passerines. To investigate the relationship between brood size, growth, and steroid hormone production in eastern Bluebirds, we cross-fostered nestlings to small, medium, and large broods. Body mass, skeletal size, serum testosterone, and baseline serum corticosterone concentration were measured prior to fledging. Bluebird nestlings raised in large broods weighed less than nestlings in small and medium-sized broods and secreted elevated concentrations of testosterone. Nestling corticosterone concentrations did not vary in response to brood size or body condition, but concentrations were higher in males compared to females. Our results suggest that nestling Bluebirds experiencing nutritional and social stress increase testosterone production. Elevated concentrations may enhance begging and competitive abilities in smaller young. Higher concentrations of corticosterone in males may be related to sex-biased provisioning. Further experimental work is needed to ascertain the effects of elevated testosterone concentrations in nestling Bluebirds, as well as the causes and consequences of elevated corticosterone for male nestlings.
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The effects of brood size on growth and steroid hormone concentrations in nestling eastern Bluebirds (Sialia sialis)
General and Comparative Endocrinology, 2011Co-Authors: Corinne P. Kozlowski, Robert E RicklefsAbstract:Abstract Birds in multi-nestling broods often experience reduced growth and elevated nutritional and social stress as a result of competition for parental resources. While responses are often species-specific, experimentally increasing brood size has been shown to decrease growth and increase production of both testosterone and corticosterone in nestling passerines. To investigate the relationship between brood size, growth, and steroid hormone production in eastern Bluebirds, we cross-fostered nestlings to small, medium, and large broods. Body mass, skeletal size, serum testosterone, and baseline serum corticosterone concentration were measured prior to fledging. Bluebird nestlings raised in large broods weighed less than nestlings in small and medium-sized broods and secreted elevated concentrations of testosterone. Nestling corticosterone concentrations did not vary in response to brood size or body condition, but concentrations were higher in males compared to females. Our results suggest that nestling Bluebirds experiencing nutritional and social stress increase testosterone production. Elevated concentrations may enhance begging and competitive abilities in smaller young. Higher concentrations of corticosterone in males may be related to sex-biased provisioning. Further experimental work is needed to ascertain the effects of elevated testosterone concentrations in nestling Bluebirds, as well as the causes and consequences of elevated corticosterone for male nestlings.
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IMMUNE AND GROWTH RESPONSE OF WESTERN BluebirdS AND ASH-THROATED FLYCATCHERS TO SOIL CONTAMINANTS
Ecological Applications, 2003Co-Authors: Jeanne M. Fair, Orrin Myers, Robert E RicklefsAbstract:During the past two decades, a critical need has developed to determine how exposure to contaminants in the environment affects individual and population processes. In this study, the immunocompetence of Western Bluebirds (Sialia mexicana) and Ash- throated Flycatchers (Myiarchus cinerascens) was studied on a landscape-soil contaminant gradient at Los Alamos National Laboratory (LANL) in New Mexico during 1997-1999. A variety of contaminants (heavy metals, chemicals, insecticides, polychlorinated biphenyls, and radioactive isotopes) range across different spatial scales and concentrations on LANL land. The two species have similar life-history traits, except that the Ash-throated Flycatcher has a faster rate of development and fledges 4-5 days earlier than the Bluebird. The number of active nest boxes increased from 1997 to 1998 and 1999 for the Western Bluebird, but not for the Ash-throated Flycatcher. Survival of nestling flycatchers was lower in areas within 60 m of a potential contaminant release site, with a higher survivorship function associated with boxes farther away. The two species did not differ in their response to antigens, and there was no difference between locations for immunocompetence for either species. Flycatcher nestlings had a higher average cell-mediated response than Bluebird nestlings, as predicted by the faster rate of development of the flycatchers. Phytohemag- glutinin response varied between locations for both species. The cell-mediated effects were dynamic in that, in general, the same locations showed similar patterns for each year. Hematocrits steadily increased with age for both species and varied between locations for the Bluebird, but not the flycatcher.
Corinne P. Kozlowski - One of the best experts on this subject based on the ideXlab platform.
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The effects of brood size on growth and steroid hormone concentrations in nestling eastern Bluebirds (Sialia sialis)
General and Comparative Endocrinology, 2011Co-Authors: Corinne P. Kozlowski, Robert E RicklefsAbstract:Abstract Birds in multi-nestling broods often experience reduced growth and elevated nutritional and social stress as a result of competition for parental resources. While responses are often species-specific, experimentally increasing brood size has been shown to decrease growth and increase production of both testosterone and corticosterone in nestling passerines. To investigate the relationship between brood size, growth, and steroid hormone production in eastern Bluebirds, we cross-fostered nestlings to small, medium, and large broods. Body mass, skeletal size, serum testosterone, and baseline serum corticosterone concentration were measured prior to fledging. Bluebird nestlings raised in large broods weighed less than nestlings in small and medium-sized broods and secreted elevated concentrations of testosterone. Nestling corticosterone concentrations did not vary in response to brood size or body condition, but concentrations were higher in males compared to females. Our results suggest that nestling Bluebirds experiencing nutritional and social stress increase testosterone production. Elevated concentrations may enhance begging and competitive abilities in smaller young. Higher concentrations of corticosterone in males may be related to sex-biased provisioning. Further experimental work is needed to ascertain the effects of elevated testosterone concentrations in nestling Bluebirds, as well as the causes and consequences of elevated corticosterone for male nestlings.
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The effects of brood size on growth and steroid hormone concentrations in nestling eastern Bluebirds (Sialia sialis)
General and Comparative Endocrinology, 2011Co-Authors: Corinne P. Kozlowski, Robert E RicklefsAbstract:Abstract Birds in multi-nestling broods often experience reduced growth and elevated nutritional and social stress as a result of competition for parental resources. While responses are often species-specific, experimentally increasing brood size has been shown to decrease growth and increase production of both testosterone and corticosterone in nestling passerines. To investigate the relationship between brood size, growth, and steroid hormone production in eastern Bluebirds, we cross-fostered nestlings to small, medium, and large broods. Body mass, skeletal size, serum testosterone, and baseline serum corticosterone concentration were measured prior to fledging. Bluebird nestlings raised in large broods weighed less than nestlings in small and medium-sized broods and secreted elevated concentrations of testosterone. Nestling corticosterone concentrations did not vary in response to brood size or body condition, but concentrations were higher in males compared to females. Our results suggest that nestling Bluebirds experiencing nutritional and social stress increase testosterone production. Elevated concentrations may enhance begging and competitive abilities in smaller young. Higher concentrations of corticosterone in males may be related to sex-biased provisioning. Further experimental work is needed to ascertain the effects of elevated testosterone concentrations in nestling Bluebirds, as well as the causes and consequences of elevated corticosterone for male nestlings.
Janis L. Dickinson - One of the best experts on this subject based on the ideXlab platform.
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cooperation and competition nepotistic tolerance and intrasexual aggression in western Bluebird winter groups
Animal Behaviour, 2009Co-Authors: Janis L. Dickinson, Melody Euaparadorn, Katherine R Greenwald, Chandreyee Mitra, Daizaburo ShizukaAbstract:Two hypothesized benefits of delayed dispersal are access to resources and prolonged brood care (or parental nepotism). Resource abundance (mistletoe wealth) is a key factor influencing whether sons stay home in western Bluebirds, Sialia mexicana, but nepotism is also observed. Western Bluebird sons commonly remain in their family groups throughout the winter, whereas daughters usually disperse before winter. Because pairing often takes place in winter groups, with newly formed pairs settling on exclusive all-purpose territories in spring, selection for sexual competition and nepotism co-occur and may simultaneously influence patterns of aggression within groups. We measured aggression at mealworm feeder stations, finding evidence of (1) intrasexual aggression against unrelated group members by experienced breeders of both sexes and (2) nepotism towards sons and daughters by experienced breeder females but not by experienced breeder males. Females showed much higher levels of aggression towards same-sex immigrants than males did. Experienced breeder males did not evict their sons from the natal territory, but they were 12 times more aggressive towards sons than breeder females were towards daughters. They were also equally aggressive towards sons and immigrant males, suggesting that local breeding competition and the benefits of intrasexual dominance counter the benefits of paternal nepotism towards sons.
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Interspecific Egg-dumping by a Violet-green Swallow in an Active Western Bluebird Nest
The Wilson Journal of Ornithology, 2007Co-Authors: Danika Kleiber, Jenne Turner, Amber E. Budden, Janis L. DickinsonAbstract:Abstract We observed a Violet-green Swallow (Tachycineta thalassina) laying an egg in an active Western Bluebird (Sialia mexicana) nest. The Western Bluebird male and not the female, was aggressive to the Violet-green Swallow but the swallow remained to lay the egg. This is the first documented incidence of which we are aware involving altricial interspecific egg-laying during the nestling phase. We suggest the timing of this event was more consistent with incidental egg deposition, or egg-dumping, than brood parasitism or nest usurpation.
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Male share of provisioning is not influenced by actual or apparent loss of paternity in western Bluebirds
Behavioral Ecology, 2003Co-Authors: Janis L. DickinsonAbstract:Approximately 45% of western Bluebird (Sialia mexicana) females have some chicks in the nest that are not sired by their social mates. Extrapair fertilizations account for 42% of offspring in these nests and 19% of nestlings overall. I tested the hypothesis that males reduce nestling provisioning when their certainty of paternity or share of paternity is reduced. Capture and detention of socially monogamous males for 1 h or 24 h during the laying period reduced males' copulatory access and their ability to mate guard, increasing the frequency with which extrapair males intruded and attempted to copulate with resident females. Males detained during laying did not reduce their share of feeding trips compared to control males detained during incubation, compared to unmanipulated males, or compared to males that were captured but not detained. Males detained on territory for 1 h during the laying period did not reduce their share of feeding trips when they observed male intrusion, nor when they observed their mates accepting extrapair copulations. Males that witnessed their mates accepting extrapair copulations did not reduce their share of risk in provisioning. Genetic fingerprinting at nonexperimental nests indicated that males also failed to reduce their feeding contributions when their estimated share of paternity was reduced, even when a helper male was present to reduce the impact on nestlings. These results suggest that male western Bluebirds do not make significant adjustments in their share of provisioning when they have evidence of partial paternity loss. Together with prior results, this study suggests that western Bluebird males use an all-or-none rule, contributing approximately half of the parental provisioning at nests, as long they have some copulatory access to the female during egg laying. Copyright 2003.
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Mate attendance and copulatory behaviour in western Bluebirds: evidence of mate guarding
Animal Behaviour, 1996Co-Authors: Janis L. Dickinson, Marty L. LeonardAbstract:Abstract The western Bluebird,Sialia mexicana, is a socially monogamous passerine with extra-pair offspring in over one-third of nests. Copulatory behaviour and mate attendance were observed for 5 years to determine whether males protect their paternity by mate guarding. Western Bluebirds copulated frequently but the frequency of copulation did not increase in the hour after laying, when fertilization is thought to occur. Males attempted to copulate with their mates at a steady rate from 60 days before laying until the onset of incubation. Female acceptance of within-pair copulations increased to 80% 10 days before laying and remained high throughout the laying period. Proximity of paired males and females corresponded with changes in the frequency of within-pair copulation attempts, but following of females by their mates corresponded with peak receptivity of females to copulation. Neither proximity nor following corresponded with temporal changes in the rate ofcourtship feeding. Pairs were closer and following of the female more frequent when nearest neighbour distances were reduced, as expected with mate guarding if the threat of extra-pair copulation increases with local density. Pairs were also closer when vegetative cover around the nest increased, suggesting that one function of mate attendance may be to keep the female in view. Male western Bluebirds may ensure their paternity by thwarting extra-pair copulations and by increasing copulatory access; however, paternity assurance provides a more comprehensive explanation than copulatory access for spatial and temporal variation in associative behaviours of pairs.
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Fitness consequences of helping behavior in the western Bluebird
Behavioral Ecology, 1996Co-Authors: Janis L. Dickinson, Walter D. Koenig, Frank A. PitelkaAbstract:We examined the fitness consequences of helping behavior in the western Bluebird (Sialia mexicand) at Hastings Reservation in Carmel Valley, California, USA, and tested hypodieses for how helpers benefit from engaging in alloparental behavior. Both juvenile and adult western Bluebirds occasionally help at the nest. During a 12 year period, all adult helpers and most juvenile helpers were male. Helpers usually fed at nests of both their parents and rarely helped when only one parent was present. The frequency of pairs with adult helpers was only 7%, but nearly one-third of adult males helped among those with both parents on the study area. At least 28% were breeders whose nests failed. The propensity to help appears to depend upon parental survival, male philopatry, and die breeding success of potential helpers. Feeding rates were not increased at nests with juvenile helpers, apparendy because breeding males reduced their feeding rates. In contrast, adult helpers increased die overall rates of food delivery to die nest in spite of a reduction in die number of feeding trips made by both male and female parents. Helpers did not derive any obvious direct fitness benefits from helping, but diey had greater indirect fitness than nonhelpers due to increases in nesding growdi rates and fledging success at dieir parents' nests. Helpers fledged fewer offspring in their first nests dian did nonhelpers, suggesting diat they were birds widi reduced reproductive potential. Aldiough we have not yet measured the effect of extrapair fertilizations on die fitness benefits of helping, we calculated die difference in fitness between helpers and nonhelpers as a function of die potential helper's paternity when breeding independendy and his fadier's paternity in die nest at which he might help. In conjunction with constraints on breeding and indirect fitness benefits, we predict that relatedness of males to die young in dieir own as well as dieir parents' nests will influence helping behavior in western Bluebirds.
Daniel A Cristol - One of the best experts on this subject based on the ideXlab platform.
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reproductive success and developmental stability of eastern Bluebirds on golf courses evidence that golf courses can be productive
Wildlife Society Bulletin, 2005Co-Authors: Joshua E Leclerc, John P. Swaddle, Daniel A CristolAbstract:We assessed adult reproductive and nesting success, and developmental instability, survival, and condition of nestling eastern Bluebirds (Sialia sialis) breeding in nestboxes on and off golf courses. With this information we tested hypotheses predicting that nestboxes on golf-course habitat provided poor nesting and chick-rearing environments due to pesticide pollution or other factors. Contrary to our prediction, nestboxes on golf courses received 28% more Bluebird eggs and produced 17% more fledglings than nestboxes on nongolf sites. Individual nests on golf courses appeared to have slightly reduced probabilities of survival during laying and incubation, but we found no depression in the overall Mayfield survival probabilities. Surprisingly, nestling Bluebirds raised in golf-course boxes exhibited 39% less fluctuating asymmetry of their tarsus bones, possibly an indicator that nestlings that survived to fledge had been under less stress during development. This may have resulted from stronger selection against asymmetrical nestlings on golf courses, or it may indicate that golf-course nestboxes provide higher-quality habitat for Bluebirds. Our results suggest that for this bird species, nestboxes on the golf-course habitat we studied can provide high-quality rearing environments and may serve as population sources. This may not apply to other species, including most birds of conservation concern, which do not nest in protected artificial cavities or forage directly on turfgrass habitat.
Joshua E Leclerc - One of the best experts on this subject based on the ideXlab platform.
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reproductive success and developmental stability of eastern Bluebirds on golf courses evidence that golf courses can be productive
Wildlife Society Bulletin, 2005Co-Authors: Joshua E Leclerc, John P. Swaddle, Daniel A CristolAbstract:We assessed adult reproductive and nesting success, and developmental instability, survival, and condition of nestling eastern Bluebirds (Sialia sialis) breeding in nestboxes on and off golf courses. With this information we tested hypotheses predicting that nestboxes on golf-course habitat provided poor nesting and chick-rearing environments due to pesticide pollution or other factors. Contrary to our prediction, nestboxes on golf courses received 28% more Bluebird eggs and produced 17% more fledglings than nestboxes on nongolf sites. Individual nests on golf courses appeared to have slightly reduced probabilities of survival during laying and incubation, but we found no depression in the overall Mayfield survival probabilities. Surprisingly, nestling Bluebirds raised in golf-course boxes exhibited 39% less fluctuating asymmetry of their tarsus bones, possibly an indicator that nestlings that survived to fledge had been under less stress during development. This may have resulted from stronger selection against asymmetrical nestlings on golf courses, or it may indicate that golf-course nestboxes provide higher-quality habitat for Bluebirds. Our results suggest that for this bird species, nestboxes on the golf-course habitat we studied can provide high-quality rearing environments and may serve as population sources. This may not apply to other species, including most birds of conservation concern, which do not nest in protected artificial cavities or forage directly on turfgrass habitat.