Current research
My research interests now fall into two areas:
Studies on natural incubation by birds
Studies on natural incubation are focused on two aspects of the reproductive biology of the Mandarin Duck Aix galericulata:
- water economy of the egg in the nest
- brood parasitism.
The Mandarin Duck is an intraspecific brood parasite, and in consequence clutch sizes can reach very large numbers; sometimes as many as 40 or more. As this is a cavity-nesting species this could have important consequences for the water balance of the egg within a clutch. At present research on the water economy of the egg is concerned with the nature of changes in the egg water vapour conductance during natural incubation, as it relates to the structure of the shell and its cuticular covering. I am currently continuing to relate field measurements of conductance to shell structure. With Kate Graeme-Cook we have been examining the role of the microbial flora on the shell surface during incubation. In natural incubation the shell conductance increases in the first two weeks (this does not occur in artificial incubation). During this period there are substantial changes in the shell surface microflora with the emergence of a single bacterium as the predominant species. We are continuing to investigate the possibility that it is bacterial action that is responsible for changes in shell permeability. Additionally, the clutch sizes incubated and hatches of individually marked females hvae been studied at my study site in South-east England for over 15 years: this has provided valuable data on variation in intraspecific brood parasitism of individual females during their reproductive lifetime.
These studies now feature at 'Planet Earth' website - click here to visit. Further information can be found at the dedicated website using a 
Embryonic physiology of poultry
Ion and water transfer across the blastoderm
Early in embryonic development of the avian embryo the water located within the egg white is relocated into the yolk sac prior to its movement into the embryo and other extra-embryonic compartments. Studies with Elsiddig Babiker in our laboratory have shown that a lack of egg turning impairs this process. Transport of sodium ions across the blastoderm depends upon an amiloride-sensitive transporter and is also carbonic anhydrase dependent. Water transport is isosmotic, although there is a small difference in osmotic concentration between the albumen and yolk sac.
George Latter, a graduate student in this laboratory, continued these studies on the effects of a lack of egg turning upon the sodium ion concentrations of the egg albumen, both in fertilised and unfertilised eggs. His results indicate that the effect of egg turning is to dissipate gradients in sodium concentration within the albumen which are present from the time the egg is laid. These are generated by the substantial differences in concentration of sodium between albumen and yolk. There seems to be no role for active transport of this ion in the production of these gradients as they are present both in unincubated eggs and in unfertilised eggs.
The importance for the embryo is that static incubation impairs the transfer of water from albumen to yolk sac and so to embryonic tissues. As sodium concentration gradients are present at lay storage regimes for eggs could substantially affect subsequent redistribution of water within the egg.
Interestingly, the earlier observations of Babiker and Baggott (1995) on the importance of carbonic anhydrase in blastoderm fluid transport have been confirmed and extended by George Latter (Latter and Baggott, 2002). Carbonic anhydrase is located as a type IV enzyme on the lateral plasma membranes of the endodermal cells of the blastoderm, and it would appear that this enzyme is the provider of hydrogen ions, which are essential to the process of fluid secretion linked to sodium transport.
Excretion by the avian embryo
Studies in this laboratory with Phil Bradfield have established that avian embryos subjected to high rates of water loss during incubation excrete more uric acid, but that this has complex effects upon the ion balance of the allantoic fluid, which effectively acts as an indicator of kidney function. We conclude that the composition and volume of allantoic fluid has little to do with a reserve function - the accepted orthodoxy - but much more to do with reflecting the effects of hydration status of the embryo upon the functioning of the embryonic kidney.
Eggshell characteristics and incubation
Dr Charles Deeming and I are currently examining the ultrastructure and functional characteristics of the shell of the Houbara (Chlamydotis undulata macqueenii). This endangered species is in the Arabian and Saharan deserts, and the material is supplied to us by the National Wildlife Research Centre, Tai'if, saudi Arabia.
