Age of First Breeding in Merlins (Falco columbarius)

Lieske, David J.; Oliphant, Lynn W.; James, Preston E.; Warkentin, Ian G.; Espie, Richard H. M.

doi:10.2307/4089170

Cited by 10 publications

(2 citation statements)

References 12 publications

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“…Average brood size at ringing was 4.17 AE 0.88 sd young per nest (range 1 to 5), with average proportion male of 0.49 AE 0.22 sd (range 0-1). The average age of the associated adult male for these nests was 2.8 AE 1.5 sd years (range 1-8 years); among females of known age, the average age was 2.9 AE 1.9 sd years (range 1-8 years) with dichotomous age class allocations for the associated adult females being 64 first-time breeders (assumed 1-year-old, Lieske et al 1997) and the remaining 63 individuals aged older than 1 year. Hatch date average was day 165 AE 7 sd of the year (range day 151-182; equating to 31 May to 1 July).…”

Section: Resultsmentioning

confidence: 99%

“…From this sample, there were only 37 nests where both female and male were birds of known age with eggs hatched in the nests to provide data on brood sex ratio. Hence, our brood-level analyses were based on the 127 nests from this 13-year period for which we had known-age males and females that could be assigned dichotomously to either age 1 (based on ringing as a nestling or because they were detected breeding for the first time in our population; Lieske et al 1997) or an after-second-year category (again based on ringing either as a chick or breeding adult), with eggs hatched in the nest to provide brood sex ratio data.…”

Section: Study Populationmentioning

confidence: 99%

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Brood sex ratios in Merlins reflect characteristics of the associated breeding male and population density

Warkentin

Brooks

Lieske

et al. 2022

Ibis

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Population‐level estimates of offspring sex ratios in birds typically approximate parity whereas biased ratios within nests are not uncommon. In sexually dimorphic raptors, the costs and relative fitness benefits of rearing male and female progeny vary with changing environmental circumstances. This may lead to substantial deviations from balanced investment in offspring of a particular sex by individual parents. Based on a 13‐year dataset for breeding Merlins Falco columbarius in Saskatoon, Canada, we used a model selection approach to assess the influence of parents, nest‐mates and nesting area on brood sex ratio during the nestling phase. The best model for predicting brood sex ratio included age of the breeding male and brood size for each nest (n = 127); nests with older male breeders and smaller brood sizes had more female young. The population‐level annualized average proportion of male offspring was 0.472 ± 0.017 (mean ± standard error), but tended towards greater production of female young during an initial period of population growth (8 years, 10–21 pairs; proportion male 0.435 ± 0.031) versus a period when the population fluctuated around a presumed carrying capacity (11 years, 24–33 pairs; proportion male 0.500 ± 0.017). Energetics appears to be a finely tuned mechanism driving sex ratio allocation in Merlins at both brood and population levels. Provisioning food for young in the nest represents the male's ability to successfully capture prey, reflecting his age and/or experience, as well as the availability of prey to the male. Confounding this mechanism to determine sex ratio allocation are the pressures created by population dynamics that dictate competition for resources both within the nest (brood size) and external to the nest (population density).

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Section: Resultsmentioning

confidence: 99%

Section: Study Populationmentioning

confidence: 99%

Brood sex ratios in Merlins reflect characteristics of the associated breeding male and population density

Warkentin

Brooks

Lieske

et al. 2022

Ibis

Self Cite

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Does breeding population trajectory and age of nesting females influence disparate nestling sex ratios in two populations of Cooper's hawks?

Rosenfield

Stout

Giovanni³

et al. 2015

Ecology and Evolution

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Offspring sex ratios at the termination of parental care should theoretically be skewed toward the less expensive sex, which in most avian species would be females, the smaller gender. Among birds, however, raptors offer an unusual dynamic because they exhibit reversed size dimorphism with females being larger than males. And thus theory would predict a preponderance of male offspring. Results for raptors and birds in general have been varied although population‐level estimates of sex ratios in avian offspring are generally at unity. Adaptive adjustment of sex ratios in avian offspring is difficult to predict perhaps in part due to a lack of life‐history details and short‐term investigations that cannot account for precision or repeatability of sex ratios across time. We conducted a novel comparative study of sex ratios in nestling Cooper's hawks (Accipiter cooperii) in two study populations across breeding generations during 11 years in Wisconsin, 2001–2011. One breeding population recently colonized metropolitan Milwaukee and exhibited rapidly increasing population growth, while the ex‐Milwaukee breeding population was stable. Following life‐history trade‐off theory and our prediction regarding this socially monogamous species in which reversed sexual size dimorphism is extreme, first‐time breeding one‐year‐old, second‐year females in both study populations produced a preponderance of the smaller and cheaper sex, males, whereas ASY (after‐second‐year), ≥2‐year‐old females in Milwaukee produced a nestling sex ratio near unity and predictably therefore a greater proportion of females compared to ASY females in ex‐Milwaukee who produced a preponderance of males. Adjustment of sex ratios in both study populations occurred at conception. Life histories and selective pressures related to breeding population trajectory in two age cohorts of nesting female Cooper's hawk likely vary, and it is possible that these differences influenced the sex ratios we documented for two age cohorts of female Cooper's hawks in Wisconsin.

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Reproductive Strategies

Leonardi¹

2020

Behavioural Ecology of Western Palearctic Falcons

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Age of First Breeding in Merlins (Falco columbarius)

Cited by 10 publications

References 12 publications

Brood sex ratios in Merlins reflect characteristics of the associated breeding male and population density

Brood sex ratios in Merlins reflect characteristics of the associated breeding male and population density

Does breeding population trajectory and age of nesting females influence disparate nestling sex ratios in two populations of Cooper's hawks?

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