The impact of Paradise shelducks (Tadorna variegata) on pastoral communities and their role as reservoirs af agricultural diseases : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Ecology, Massey University, Auckland
Since its habitat expansion, due to human land clearance for farmland, paradise shelducks (Tadorna variegata) have established a firm foothold in the New Zealand agricultural environment. Paradise shelducks feed primarily on agricultural pasture and consequently compete directly with livestock for resources. As a result many farmers consider paradise shelducks to be a pest. In addition, it is a common perception that paradise shelducks contaminate agricultural land with their faeces. Although there is a wealth of information on the impacts of waterfowl on agricultural industries and diseases associated with waterfowl, no studies have specifically looked at the potential impact paradise shelducks pose on New Zealand's agricultural practices. The aims of this study were to 1) determine the presence and prevalence of pathogenic micro-organisms in paradise shelduck faeces and their associated environment, 2) evaluate the findings in terms of transmission routes and the relative risk to livestock and humans, 3) determine whether paradise shelducks have an affect on primary pasture production and composition, and 4) estimate the daily food intake rates of paradise shelducks. This study was based on a population of paradise shelducks in Tawharanui Regional Park over each of four seasons from 2006-2007. The prevalence of pathogenic micro-organisms was determined by paradise shelduck faecal surveys for selected bacteria and parasites. Surveys were conducted for flock birds and breeding pairs Additionally, faecal samples of sympatric species and water troughs were analysed. The impacts of paradise shelducks on pastoral communities was assessed by means of an exclusion experiment, consisting of two types of exclosure; a 'closed' exclosure to exclude all animals including paradise shelducks, and an 'open' exclosure to exclude livestock, but to allow access for paradise shelducks. Daily food intake rates for paradise shelducks were estimated from observational foraging data and necropsies ot paradise shelducks. Results show that no isolates of Salmonella. Campylobacter Yersinia. Cyrptospordium or Giardia were found. Relatively low prevalences of non haemolytic and alpha haemolytic Streptococci. Enterococcus, Bacillus, Clostridium perfringens, Proteus mirablis, strongyle eggs and Coccidia eggs were found. Additionally. E. coli was consistently isolated from the faecal samples throughout the sampling period. However, the serotypes of the micro-organisms isolated were not determined, so no conclusions could be drawn in relation to their pathogenicity. Furthermore, no significant correlations were found between the number of accumulated faeces sampled and the presence or prevalences of the micro-organisms isolated. It also appears that sampling during the driest times of the year will yield the highest presence of micro-organisms in paradise shelduck faeces. An array of micro-organisms, similar to those found in paradise shelduck faeces, were found in pukekos and house sparrow faeces as well as high contamination levels of faecal indicators in troughs. No conclusive transmission routes for the micro-organisms were found. Paradise shelducks were found to have a significant impact on pasture production and to selectively graze white clover (Trifolium repens). Furthermore, it was estimated that the paradise shelducks had a foraging intake rate of 104±15g/day of pasture dry matter. The results confirmed that paradise shelducks can have an affect on agricultural land. A more long term study in different regions is required to evaluate the full extent to which paradise shelducks affect agricultural production in New Zealand.