Corticosterone responses to captivity and sampling stress in mallard (Anas platyrhynchos) and grey duck (Anas superciliosa) : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Physiology at Massey University
1. The aim of this study was to investigate the influence of capture and captivity stress on plasma corticosterone levels and breeding success in mallard and grey ducks. Measurements of plasma corticosterone levels were used to identify factors that cause stress and to identify individual birds with low stress responses and a greater likelihood of a successful breeding in captivity than their peers. The effect on corticosterone levels of the stress associated with the collection of blood samples was investigated and different sampling regimes for measuring corticosterone responses to stress were examined. The use of exogenous glucose administration and the placing of ducks into darkened boxes to lower corticosterone levels was also studied.
2. Corticosterone levels in wild mallards after capture were higher than levels in ducks held captive for 3 or 5 months. Corticosterone levels decreased in captive ducks in relation to the time spent in captivity and amount of contact spent with people.
3. Corticosterone levels repeatedly measured over 8 months varied between individual captive grey duck. The only 2 female ducks to rear ducklings, and their mates, all had lower corticosterone levels before the breeding season than the remaining 4 female and 3 male ducks.
4. The variation in corticosterone levels and responses between individual grey duck and the negative relationship between corticosterone levels and body weight may have been due, in part, to the existence of a dominance hierarchy amongst the grey ducks.
5. Corticosterone levels in winter may indicate potential breeding success and, can be used to identify stressful factors in the captive environment.
6. The observation of an increase in corticosterone levels with the sampling and handling of ducks depends on the magnitude of levels in the first sample obtained and on the frequency with which samples are obtained thereafter.
7. High corticosterone levels will decrease if a duck is placed in a darkened individual box or given an oral dose of 10 ml of 0.84M or 1.38M
8. It is concluded that the measurement of corticosterone levels can be used to indicate factors that may affect the breeding performance of birds. Methods for minimising the stress associated with the capture and captivity of wild birds can also be identified from the measurement of corticosterone levels.