The effects of different sample storage conditions on faecal corticosterone metabolite measurements in northern bobwhite (Colinus virginianus).

The northern bobwhite (Colinus virginianus) is an economically and ecologically vital gamebird in North America experiencing vast population declines. With the recent validation of an enzyme immunoassay to detect corticosterone metabolites in faeces, there are many opportunities for its scientific application. Corticosterone, a key avian stress-related hormone, has many beneficial functions that support a quail's immune response, primarily by suppressing inflammation, allowing cells to function more efficiently. However, chronic levels of elevated corticosterone in Aves have been shown to cause metabolic disruption and suppressed reproduction and growth. Determining root causes of chronically elevated corticosterone levels is vital for bobwhite conservation efforts. Proposed research investigating causes of bobwhite stress includes examining the effects of pesticides, climate, disease and management strategies. However, the various methodologies exploring these relationships may result in different ways the faeces are stored and processed, especially in studies on wild bobwhite. These differences may impact research outcomes leading to incorrect conclusions. This study was conducted to determine if enzyme immunoassay results from faecal samples frozen or left in the environment before extraction of faecal corticosterone metabolites differ from those where extraction is immediate. Faeces treatments affected the corticosterone metabolite measurements differently depending on whether the faeces were from males or females, so the effects of treatments were analysed within each sex. No significant difference was found in female faecal corticosterone metabolite concentrations between the frozen and environmentally exposed faeces (P = 0.853); however, concentrations in the immediately extracted faecal corticosterone metabolites were significantly lower (P < 0.001). Male bobwhite faecal samples that were immediately frozen had significantly lower faecal corticosterone metabolite concentrations compared to environmentally exposed male samples and frozen female samples (P = 0.039). These results indicate that faecal corticosterone metabolite concentrations are comparable between environmentally exposed samples from both sexes and frozen samples from females.