Effects of natural weathering conditions on faecal cortisol metabolite measurements in the greater bilby (Macrotis lagotis)

Abstract

Natural weathering conditions can influence faecal cortisol metabolite (FCM) measurements in wildlife if fresh faeces cannot be collected immediately following defaecation. In this study, we evaluated this issue in a threatened Australian marsupial, the greater bilby (Macrotis lagotis). Fresh (<12 h since defaecation) faecal samples (n = 19 pellets per bilby) were collected one morning from seven adult bilbies kept in captivity. One control faecal sample (Day 1) from each bilby was immediately frozen. The remaining faecal pellets were randomly positioned outdoors. Subsequently, we froze one faecal pellet every 24 h for 19 days. FCM levels in bilby faeces were quantified using an enzyme-immunoassay. Mean FCM levels showed variation (daily mean coefficients of variation [CV %]) of 56.83–171.65% over 19 days. Overall, FCM levels were affected by exposure time; however, multiple comparisons showed that no significant change in FCM occurred after environmental exposure (no significant difference in mean FCM between control (Day 1) with any of the exposure days (Days 2–19). Individuals and sex also affected FCM levels. We found no correlation between mean daily CVs with daily minimum–maximum temperatures or rainfall. Our results indicate that FCM in bilby faeces is fairly stable to long-term environmental exposure (19 days). In future, freshly excreted bilby faeces (where the sample maintains a distinct odour for 9–13 days) should be used to study FCM levels in wild bilbies.

Monitoring physiological stress in semi-free ranging populations of an endangered Australian marsupial, the Greater Bilby (Macrotis lagotis)

“…1 Individual fecal cortisol metabolite concentrations (ng/g net dry weight) in bilby subjected to adrenocorticotropic hormone (ACTH) challenge. Day of injection is depicted using vertical dashed line old) bilby feces are fairly stable to natural weathering conditions up to 13 days; that is, the FCMs in these feces are not deteriorated (Evans et al 2013). Therefore, our sampling methods using transects provide a reliable way of obtaining fresh bilby fecal samples that will eventually be used for indicating the physiological sensitivity of semi-free ranging populations against environmental threats such as stochastic weather events (storms and droughts) and predation by feral pests.…”

“…We analysed bilby fecal extracts for concentrations of FCM using enzyme immunoassay (EIA) previously described for other mammals (Wielebnowski et al 2002;Millspaugh and Washburn 2004), and recently used for a captive subpopulation of the greater bilby (Narayan et al 2012;Evans et al 2013). Laboratory validation was done using accuracyrecovery checks and parallelism.…”

Maximizing the reliability of non-invasive endocrine sampling in the tiger (Panthera tigris): environmental decay and intra-sample variation in faecal glucocorticoid metabolites

“…African elephant, Foley et al ., 2001 ; Iberian lynx, Jewgenow et al ., 2006 ; Vargas et al ., 2008 ; greater bilby, Narayan et al , 2012 ; koala, Narayan et al ., 2013b ). Despite such a strong emphasis on methodological validation, focus has somewhat been diverted away from the necessity to explore potential sources of error that can arise much earlier in the field sampling process, especially during sample collection and processing ( Barja et al ., 2012 ; Descovich et al ., 2012 ; Evans et al ., 2013 ).…”

“…Hormone deterioration because of bacterial degradation in faeces is a major source of FCM variation ( Beehner and Whitten, 2004 ). In instances where samples cannot be collected immediately and preserved (such as remote field studies), bacterial enzymes present in the faeces have been reported to degrade or alter hormone metabolite concentrations in samples that are left untreated, which increases the variation in glucocorticoid metabolites ( Touma and Palme, 2005 ; Evans et al ., 2013 ). The increased variation owing to natural weathering effects on faecal samples exposed to the environment can confound results and minimize the reliability of non-invasive endocrine methods for use in field conditions.…”

“…These results are possibly a result of the vastly different composition and nature of animal faeces and patterns of metabolism ( Descovich et al ., 2012 ). Evans et al . (2013) showed that FCMs were fairly stable to degradation by natural weathering in the endangered greater bilby ( Macrotis lagotis ); however, they also recommended collection of fresh samples with distinct odour for determining changes in FCMs in samples exposed to the natural environment.…”