Marshall, Ashleigh Fleming; (2023) Why do eggs fail? An investigation into hatching failure in wild and managed bird populations. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A 2022 assessment by BirdLife International found that around 13% of bird species are threatened with extinction, with an additional 9% considered Near Threatened. Conservation programmes worldwide work to protect threatened species, often establishing managed populations undergoing a range of conservation interventions as part of strategies to bring species “back from the brink”. However, an issue facing many managed threatened populations is a high incidence of hatching failure. Despite birds being among the most well- studied taxa, and improving reproductive success often being of major interest to conservation programmes, there are gaps in our understanding of the causes and underlying drivers of hatching failure in both wild and managed populations of threatened species. In my PhD, I aim to improve our understanding of why eggs fail to hatch and explore how this knowledge can be used to inform management of the species most at risk from extinction. First, I conduct a comprehensive meta-analysis examining the associations between threat status, management interventions, and avian hatching failure, finding an updated estimate of the mean overall hatching failure rate and conclusively showing that threatened and managed bird populations experience elevated rates of hatching failure. Next, by applying methods of accurately determining the fertility of unhatched eggs to several different managed populations I demonstrate how fertilisation failure rates can be overestimated, potentially leading to the application of non-optimal mitigation strategies. Following this, I characterise and compare the eggshell microbiomes of two threatened species, finding the first evidence of an effect of captivity, as well as several influential parental and environmental variables. Finally, I analyse the relationship between these threatened species’ eggshell microbiomes and hatching failure, showing that trans-shell infection may not be a major driver of hatching failure in these species and demonstrating the importance of investigating species- and population-specific drivers of hatching failure to best inform management efforts.

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