Effects of supplementary feeding on the offspring sex ratio of kakapo: a dilemma for the conservation of a polygynous parrot

Clout, Mick N.; Elliott, Graeme; Robertson, Bruce C.

doi:10.1016/s0006-3207(01)00267-1

Cited by 164 publications

(154 citation statements)

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“…Sex ratio is an important aspect of population demography and deviations from parity can have catastrophic consequences for the viability of small populations [21]. If a species alters the sex ratio of its progeny in response to the quality of the environment then developing management strategies based on demographic models that assume an equal sex ratio Grazing influences bird sex ratios G. L. Prior et al 959 could have important repercussions for species nesting in degraded habitats [22].…”

Section: Discussionmentioning

confidence: 99%

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Birds bias offspring sex ratio in response to livestock grazing

et al. 2011

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Livestock grazing, which has a large influence on habitat structure, is associated with the widespread decline of various bird species across the world, yet there are few experimental studies that investigate how grazing pressure influences avian reproduction. We manipulated grazing pressure using a replicated field experiment, and found that the offspring sex ratio of a common upland passerine, the meadow pipit Anthus pratensis , varied significantly between grazing treatments. The proportion of sons was lowest in the ungrazed and intensively grazed treatments and highest in treatments grazed at low intensity (by sheep, or a mixture of sheep and cattle). This response was not related to maternal body condition. These results demonstrate the sensitivity of avian reproductive biology to variation in local conditions, and support growing evidence that too much grazing, or the complete removal of livestock from upland areas, is detrimental for common breeding birds.

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Section: Discussionmentioning

confidence: 99%

“…21 ) and two cattle with their unweaned calves at an equivalent grazing pressure as the low sheep treatment, and ungrazed. Sheep were only removed from plots in the winter months (DecemberMarch) and cattle were added for four weeks in the autumn (for more details, see Dennis et al [4]).…”

Section: Introductionmentioning

confidence: 99%

Birds bias offspring sex ratio in response to livestock grazing

et al. 2011

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“…Endangered kakapo parrots, for instance, produce more sons when well-fed, so providing wild birds with supplementary food induces overly male-biased sex ratios unfavorable for breeding (Clout et al 2002). While failing to anticipate condition-dependent sex ratio shifts can stymie conservation attempts, factors like multiple parental conditions may be challenging to incorporate into evolutionary projections without an explicitly-demographic model.…”

Section: Sex Structurementioning

confidence: 99%

“…Condition-dependent sex ratio shifts can confound conservation attempts, as when supplementary feeding of endangered kakapo parrots induced overly male-biased sex ratios (Clout et al 2002). Alternatively, sex ratio shifts can be leveraged to promote the growth of small or vulnerable populations (Wedekind 2002).…”

Section: Introductionmentioning

confidence: 99%

Evolutionary demography of structured two-sex populations and sex ratios

Shyu¹

2015

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Males and females may differ in stage-specific survival, maturation, fertility, or mating availability. These demographic differences, in turn, affect population growth rates, equilibrium structure, and evolutionary trajectories. Models considering only a single sex cannot capture these effects, motivating the use of demographic two-sex models for sexually reproducing populations.I developed a new two-sex modeling framework that incorporates population structure and multiple life cycle processes through transition rate matrices. These models can be applied to a variety of life histories to address both ecological and evolutionary questions. Here, I apply the model to the effects of sex-biased harvest on populations with various mating systems.Demographic considerations also affect evolutionary projections.I derived matrix calculus expressions for key evolutionary quantities in my two-sex models, including the invasion fitness, selection gradient, and second derivatives of growth rates (which have many applications, including the classification of evolutionary singular strategies).I used these quantities to analyze the evolution of the primary sex ratio, under various sex-and stage-specific offspring costs and maternal conditions.Demographic two-sex models lend insight into complex, and sometimes counterintuitive, results that are not captured by models lacking population structure. These findings highlight the importance of demographic structure in ecology and evolution.

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“…When resources are abundant, females should invest more resources in the sex with the higher variance in offspring number, typically males. This insight led New Zealand conservation biologists to realize that the male-skewed sex ratio that was hampering their efforts to save the Kakapo (Strigops habroptilus, a large flightless parrot) was not merely a run of bad luck, but a response to the supplementary feeding program that was part of the conservation effort (Clout, Elliott, & Robertson, 2002). By enriching the birds' diet they were causing them to produce male offspring and endangering the survival of the species.…”

Section: Why We Cannot Do Without An Evolutionary Perspectivementioning

confidence: 99%