Determining a Buffer Distance Between Australian Commercial Chicken Farms and Water Bodies to Minimise Wild Bird Presence on Farm

Avian influenza viruses (AIVs), subdivided into Low Pathogenicity Avian Influenza (LPAI) and Highly Pathogenic Avian Influenza (HPAI), are diseases of major concern to domestic chickens worldwide (Hansbro et al., 2010). LPAI is known to circulate naturally in wild birds of the order Anseriformes (waterfowl) and Charadriiformes (shorebirds) and can potentially mutate into HPAI once transmitted to chickens (East et al., 2008). Reducing direct and indirect contact between wild birds and commercial chickens is of paramount importance to the commercial chicken industry due to the risk of AIV spillover. As surface water is an attractive habitat for wild birds, chicken sheds proximal to water bodies may be at an increased risk of virus transmission. This study aimed to determine an appropriate buffer distance between commercial chicken farms and open surface water (including dams, rivers and creeks) to minimise waterfowl and shorebird presence on future farms, and to identify current farms at risk of AIV incursion.

Sixty-four layer and broiler chicken farms in NSW and QLD (subset from the AIRisk survey, Scott et al., 2017), were located using satellite images on Google Maps (Google Inc., 2018, California, USA). The ‘measure distance’ tool was utilised to determine the distance between the closest edge of a chicken shed on each farm to the edge of the closest water body. On-farm questionnaire data specifying the presence or absence of waterfowl and shorebirds (yes/no) around farm sheds and range areas was correlated with the distance measurements. Logistic regression (Genstat, 2011, Hemel Hempstead, UK) was used to predict the relationship between waterfowl and shorebird observations around feed storage areas, the distance between the chicken shed and the closest water body, and the type of farm. Further models were included for predictions for range areas.

Regression analysis revealed a statistically significant (P = 0.03) relationship between the distance of the closest water body to the chicken shed and the sighting of waterfowl at feed storage areas. Farms which have the closest water body 101-200 m to the shed have a 56% predicted chance of sighting waterfowl at feed storage areas (P = 0.003). The predicted value at feed storage areas tended to decrease if this distance was over 200 m, although this difference was not statistically significant (P > 0.05). This finding suggests that, although waterfowl are attracted to feed areas adjacent to chicken sheds, they may be unwilling to stray further than 200 m from a water source to get there. Surprisingly, the chance of sighting a waterfowl at feed storage areas decreased if the closest water body was under 101 m away (P > 0.05). However, for shorebirds, this relationship was not significant (P = 0.21) (Table 1).

There was no significant relationship between the distance of the closest water body to the shed and sighting a waterfowl or shorebird on range areas of free-range farms (P > 0.05). This may indicate a tendency for wild birds to avoid large masses of chickens congregated at one site, perhaps to elude competition or aggression. Overgrazed, bare pastures present on free-range sites could also be a potential factor for the low observation of wild birds by the farmers (Scott et al., 2018). Our study suggests a minimum biosecurity buffer distance of 200 m from feed storage areas to the closest open water source to decrease numbers of on-farm waterfowl, although further research with a larger sample size is warranted. In addition, camera traps could be stationed on-farm to measure the frequency of wild bird visits over a longer period of time. The type of feed or vegetation on the range, on-farm biosecurity protocols relating to open water resources, feed spill protocols and use of wild bird deterrence mechanisms are additional factors that could be considered in future studies.