Urbanisation, diet, and stress
Some birds are able to readily adapt to human-modified environments; the White Ibis is one of them. This project investigates how the diet and immune response of the White Ibis in Florida is affected by moving from rural to urban habitats. Further, how might their endocrinological state be affected, particularly circulating stress hormone concentrations, and how is reproduction affected? This was in collaboration with the Navara Lab and the Hernandez Lab
A secondary project investigated the effect of human activity on nestling corticosterone responses in Eastern bluebirds, and recent work has also looked at the effect of construction noise on nesting blue tits at the University of St Andrews.
Maternal testosterone and offspring sex ratio
Sex allocation theories claim animals should adjust the sex of their offspring in response to environmental conditions, to maximise their lifetime reproductive success. Avian females can manipulate offspring sex, by influencing which sex chromosome is retained in the ovulated oocyte and which is discarded. As yet, the mechanism for sex allocation is unclear, despite wide theoretical and empirical support. This research investigates the potentially mechanistic role of circulating steroid hormones in birds (maternal testosterone in laying hens in the Navara lab). Ultimately, I hope to use this as a tool to manipulate offspring sex ratios, which would be an important development for conservation and in the poultry industry.
Wrobel ER, Molina E, Khan N, Mendonça MT, Navara KJ. (in press) Androgen and mineralocorticoid receptors are present on the germinal disc region in laying hens: Potential mediators of sex ratio adjustment in birds? General and Comparative Endocrinology.
Trans-generational effects of maternal CORT on offspring
The environment a mother experiences affects her stress hormone (corticosterone) levels, which can be transmitted to offspring via hormonal changes in the egg. This adaptive maternal effect essentially acts in conjunction with offspring genotype and other environmental influences to modify offspring phenotype, thus producing offspring that are most likely to survive to reproduce. This long-term study identified a trans-generational effect, with F2 zebra finches continuing to be affected by their grandmothers treatment. Elevated maternal stress during egg laying altered offspring hatching success, growth rates, survivorship, and even sperm quality.
See also the Robert Lab.
Stress and parental care
Reproduction is essential for species survival, and the ever-increasing stressors that birds are exposed to raises concerns for population-level health and reproduction. We used Passive Integrated Transponders (PIT tags) in combination with microchip readers, directional sensors and infra-red cameras to track parental visitation throughout the entire reproductive effort. As a result, we were able to determine nest visitation trends when one or both parents had experimentally elevated stress levels. We identified clear differences in the behaviour of chronically stressed vs unstressed birds during both incubation and chick rearing.
This is the first study, to our knowledge, to identify individual behaviour of one or both parents under chronic stress throughout their primary reproductive investment.
Night-time light pollution
As humans encroach ever more on different habitats, the animals living in these areas must adapt to a brightening night sky. Essentially, they are experiencing a simulation of longer days, which has previously been shown to affect immune function, behaviour, and reproductive cycles. This study investigates the effect of artificial light on stress hormones and reproductive timing, using the Eastern bluebird as a model species.
Genetic relatedness and experimental infections using trematode parasites (New Zealand)
Individual animals are often infected not only by different parasite species, but also by multiple genotypes of the same parasite species. This project identified key differences in parasite infectivity and growth response to density dependence and genetic relatedness, as well as developing a fluorescent dye that allows us to differentiate between different strains of trematodes, without the need for expensive DNA identification.
Artificial incubation in a critically endangered bird, the Takahe (New Zealand)
The Takahe (Porphyrio hochstetteri) is a critically endangered flightless bird, endemic to New Zealand. It is the subject of an intensive captive breeding programme, where eggs are removed from pairs to encourage double-clutching, which increases the number of juveniles each year. This particular project led to the development of guidelines establishing optimum temperatures and humidity necessary to successfully artificially incubate the young.