Raising chicks takes its toll on birds – new study

Published: 22 February 2016 at 16:30

Pair of Northern Bald Ibises

Research shows that single Northern Bald Ibis are healthier than those in pairs

New research published in the Journal of Ornithology shows that laying eggs and raising chicks can have a negative effect on the health of birds. 

Co-authored by Dr Claudia Wascher of Anglia Ruskin University, the study investigated the social interactions and health of a colony of Northern Bald Ibis (Geronticus eremita) at the Konrad Lorenz Research Station in Austria.

The scientists found that birds that were in pairs excreted a higher number of faecal samples containing parasite eggs than single birds, indicating that they are less healthy.  And females generally excreted more of these nematode eggs than males.

Egg laying is known to be energetically costly and a limiting factor for parental fitness. Therefore, the higher parasite load in females compared to males could be a result of a decreased immune system in response to the physical demands of egg laying.

The researchers also found that the higher number of ibis eggs a female laid, the higher number of parasite eggs were found in their faecal samples.  

Interestingly, this pattern reversed when looking at the number of fledglings (chicks hatching and leaving the nest), with birds excreting fewer parasites having a higher number of fledglings.  

The results suggest that the high investment in egg production impacts the caregiving towards the chicks by the parasitised female, leading to a reduced number of fledglings.

Dr Wascher, Lecturer in Animal and Environmental Biology at Anglia Ruskin, said: 

“The high parasite load in the paired Northern Bald Ibis individuals in our study highlights the high energetic demands on both sexes during reproduction and chick rearing, which may in turn affect their immune system.

“The results suggest that social behaviour, parasite burden and physiology are linked in a complex manner.  And this may be a factor not only in birds but in social vertebrates in general.

“The Northern Bald Ibis is critically endangered and so a better understanding of how the costs of reproduction affect reproductive output could help to support conservation programmes and its re-introduction into the wild.” 

The full open access paper is available to read here.