Why do eggs fail?

11 May 2021, 18:00 - 19:30

Experts discuss female reproductive failure in birds.

Hatching failure occurs in all birds, but its incidence  varies across species, populations and individuals. Small, threatened populations are particularly vulnerable, with rates of hatching failure sometimes exceeding 70%. Even large populations of common species experience an average failure rate of 10%, and this problem persists in domestic poultry despite optimised conditions and strong selection for hatching success. Egg hatchability can therefore be considered a weak link in the chain of events that determines avian reproductive success. Eggs fail for a number of reasons. In this event we will explore the different aspects that lead to female reproductive failure from gamete malfunction to developmental environment, and ask why female fertility is so poorly understood not only in birds, but across most species?

Please be aware, this event features images of bird embryos and physiology, and videos of egg dissection.


  • Dr Patricia Brekke, Institute of Zoology, ZSL: "When every egg counts: Hatching failure in conservation"
  • Dr Barbara Tschirren, Centre for Ecology & Conservation, University of Exeter: "Why do birds not lay larger eggs?"
  • Dr Nicola Hemmings, Department of Animal & Plant Sciences, University of Sheffield: "What's in an egg? The biology of avian fertilisation and why it matters for conservation"
  • Dr Jennifer Smart, Royal Society for the Protection of Birds (RSPB) Centre for Conservation Science: "The importance of breeding success in the conservation of lowland waders"
  • Gary Ward, Curator of Birds, ZSL will join the panel for this event.



  • Click here to read an extended blog post by PhD student Ashleigh Marshall exploring the problems associated with hatching failure in birds, and the methods used to identify it.
  • To read an open access review of hatching failure in birds and Animal Conservation, click here
  • For those wanting to identify the fertility status of unhatched bird eggs, a practical resources guide featuring protocols and video demonstrations can be found here.


Catch up on the event below or visit: https://youtu.be/QUOfqYhNxPg

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Science and Conservation Event Details:

  • This interactive online event was livestreamed to our YouTube channel, which can be found here: zsl.org/IoZYouTube, alongside recordings of all our previous online events.
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  • Each event will comprise of 3-4 presentations from experts in the topic, similar to our previous event series.
  • Thank you to everyone who submitted a question - we encourage you to watch our events live so you can take part!
  • There was no charge for this event, and no need to register in advance to watch the livestream.
  • This event was produced by Eleanor Darbey, hosted by Charlotte Coales and facilitated by Tendai Pottinger, ZSL.


    ZSL Wild Science Podcast

    We will be creating a fascinating podcast episode featuring some of the speakers from this event, so keep an ear out in the following months! Listen to previous episodes from our award winning ZSL Wild Science podcast episodes produced by Dr Monika Böhm, and Eleanor Darbey here


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