Skewed sex ratios in a newly established osprey population

Morandini, Virginia; Muriel, Roberto; Newton, Ian; Ferrer, Miguel

doi:10.1007/s10336-019-01680-9

Cited by 11 publications

(12 citation statements)

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“…It is important to be aware that newly established/colonizing populations can experience population dynamics that are different from stable populations, and this can have implications for estimates of temporal variation if not properly accounted for. For example, in the initial years postrelease, a population’s sex and age ratio can be unstable (Armstrong and Reynolds, 2012; Morandini et al., 2019b), whereas density dependence may cause changes in vital rates as the population grows towards carrying capacity (Manning et al. 2019; Morandini et al., 2019a).…”

Section: Discussionmentioning

confidence: 99%

Incorporating data‐based estimates of temporal variation into projections for newly monitored populations

Parlato

Ewen

McCready

et al. 2021

Animal Conservation

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The importance of accounting for temporal variation in vital rates when modelling population dynamics is well recognized. However, long‐term (usually >5 years) datasets are needed to estimate this variation. Consequently, models for newly monitored populations typically assume no temporal variation or use default values provided in software programmes, both of which can give misleading inferences about population dynamics. The goal of this study is to improve estimation of dynamics in the initial years of conservation programmes by incorporating data‐based estimates of temporal variation from other populations with longer‐term data available. We show how data‐derived priors can be generated using estimates of temporal variation in vital rates from other populations, providing information about expected variation until sufficient population‐specific data are available. We specifically evaluated whether data‐derived priors improved our ability to estimate temporal variation for a reintroduced population monitored for 3 years postrelease. We first predicted population growth and probability of extinction assuming no temporal variation in vital rates, then compared projections to those obtained when temporal variation was estimated with uniform priors or with the data‐derived priors. Both types of priors were constrained to plausible ranges, and we also assessed sensitivity of model outputs to widening those ranges. Median projected population size was similar under all three models, but extinction probability was higher with inclusion of temporal variability, reiterating the importance of incorporating this source of uncertainty. Projections with temporal variation were similar irrespective of whether data‐derived priors or uniform priors were used. However, the data‐derived priors generated more precise estimates of annual variation that were less sensitive to relaxation of prior constraints. The approach we present can facilitate management decisions at the outset of conservation programmes when risk assessments that account for all relevant uncertainties can be crucial for determining optimal management strategies.

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Section: Discussionmentioning

confidence: 99%

Incorporating data‐based estimates of temporal variation into projections for newly monitored populations

Parlato

Ewen

McCready

et al. 2021

Animal Conservation

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“…In this case, according to the environmental sex determination hypothesis, we can expect an increase in the production of the most expensive sex, because only the best territories are occupied in a low‐density situation. Under the hypothesis of age of breeders, however, an overproduction of the cheaper sex was expected during early stages of a colonization process, because first breeders are mainly young breeders (Morandini et al ). Captive breeding programs can be a very helpful resource for new insight in sex ratio deviations.…”

Section: Discussionmentioning

confidence: 99%

“…Based on these ideas, adaptive explanations for natal sex‐ratio variation among vertebrates have been subject of debate (Gowaty , Hardy , West and Sheldon , Shyu and Caswell ). Indeed, the adaptive significance of sex‐ratio variation is not well understood for populations where the natal sex ratio clearly deviated from 1:1 (Wiebe and Bortolotti , Heinsohn et al , Komdeur et al , Korpimäki et al , Ferrer et al , Morandini et al ).…”

Section: Introductionmentioning

confidence: 99%

“…A lower residual reproductive value for older parents could explain a stronger investment in the most expensive sex later in life (Trivers ), with younger breeders producing more of the cheaper sex (Blank and Nolan , Weimerskirch et al , Ferrer et al ). Nevertheless, the age of breeders and territory quality tend to be correlated, with older breeders occupying the highest quality territories (Ferrer and Bisson , Ferrer and Penteriani , Ferrer et al , Morandini et al ), therefore results obtained from observational studies should be interpreted with caution.…”

Section: Introductionmentioning

confidence: 99%

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Age of the breeders, but not territory quality, explains hatching sex ratio in booted eagles

Morandini

Baumbush

Balbontı́n

et al. 2020

Journal of Avian Biology

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Natal sex‐ratio variation is a central concept in population demography. When males and females are equally costly to rear, the population sex ratio should be 1:1, but if they differ in cost, more of the cheaper sex should be produced. According the age dependent sex ratio hypothesis, younger breeders should produce more chicks of the cheaper sex. On the other hand, the environmental sex determination hypothesis suggests that parents in poor conditions (scarce food and low‐quality territories) tend to produce more of the cheaper sex. To test hypotheses on adaptive sex ratio, we studied the booted eagle Aquila pennata, a raptor with marked sexual dimorphism, with females larger than males. We sexed 174 nestlings from 121 broods in 1996–2000 to study hatching and fledgling sex ratios. We did not find deviations of the 1:1 sex ratio at the population level during the length of the whole study period or on a yearly basis. Sex ratio was affected by age of the breeders, but not by territory quality (average productivity), quality of year, nearest nest distance or number of breeding pair in the population. Older breeders raised more females (i.e. the expensive sex), supporting the age dependent sex ratio hypothesis. In long‐lived species, older breeders tend to occupy better quality territories than younger ones, confounding some of the commonly used surrogates of territory quality, like frequency of occupation or year of first occupation; results obtained from observational studies should be interpreted with caution. We discuss alternative approaches and different scenarios that could provide new insight into the study of factors that influence sex ratio deviations in vertebrates.

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“…As noted above, there is a widespread tendency for younger breeders to produce more cheaper-to-produce male offspring, which could also account for this outcome. Late in population establishment, when carrying capacity has placed limits on the number of breeding pairs, competition for breeding resources should shift towards production of more of the furtherdispersing sex (Julliard 2000, Schrand et al 2011, Rutz 2012, Morandini et al 2019. Additional pressure to avoid inbreeding or competing with the previous years' offspring would also be expected to accelerate the shift.…”

Section: Influence Of Population Dynamicsmentioning

confidence: 99%

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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Skewed sex ratios in a newly established osprey population

Abstract: There may be differences between this version and the publisher's version. You are advised to consult the publisher's version if you wish to cite from this article.

Cited by 11 publications

References 54 publications

Incorporating data‐based estimates of temporal variation into projections for newly monitored populations

Incorporating data‐based estimates of temporal variation into projections for newly monitored populations

Age of the breeders, but not territory quality, explains hatching sex ratio in booted eagles

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

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