Microbial infection of avian eggs : a threat to all synchronously incubating species? Case study of New Zealand's little blue penguin (Eudyptula minor) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Auckland, New Zealand
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Date
2010
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Massey University
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Abstract
Microbial infection of eggs was originally investigated in terms of human health only.
Recently, however, it was found that it can also cause early embryo mortality in birds,
mainly through trans-shell infection prior to incubation. Trans-shell infection is highly
dependent upon environmental conditions, egg temperature and egg properties such as
shell quality and antimicrobial defences. Microbial infection of eggs is more likely to
occur in synchronously incubating species as first laid eggs can be exposed for up to
several days prior to full incubation. One example of a population that seems at
particular risk of egg microbial infection is New Zealand’s little blue penguin
(Eudyptula minor) from Tiritiri Matangi Island. This bird lays two eggs on average
three days apart, and is believed to begin full incubation only after the second egg has
been laid. Both eggs are laid in particularly humid and soiled nests and contain only low
levels of lysozyme, an important antimicrobial protein. The aims of this study were
therefore to 1) obtain a first examination of the rates of shell and trans-shell microbial
infection of chicken eggs in New Zealand and assess the effects of cleaning on those
rates, 2) investigate the role of microbes in hatching failure of little blue penguin eggs
and 3) investigate other factors affecting little blue penguin egg viability. This study
revealed that shell infection in chicken eggs significantly increased with exposure and
significantly decreased with cleaning; however, trans-shell infection was only
marginally affected by exposure and cleaning. On Tiritiri Matangi Island, Hauraki Gulf,
New Zealand, nest type, egg order and shell cleaning did not affect hatching success,
suggesting that nest conditions and microbial infection prior to incubation were not a
major cause of egg mortality in this population. Temporary abandonment during
incubation, however, was very frequent in the second half of the breeding season and
fatal to most eggs. These temporary abandonments seemed to be caused by resource
limitations, an aspect that should be investigated in future studies.
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Keywords
Bird mortality, Penguin, Egg shell infection