Bird damage to vegetable crops in Long Valley during winter

Abstract

Long Valley is the largest agricultural wetland in Hong Kong and supports a high level of biodiversity. The implementation of Management Agreement project in Long Valley has successfully enhanced its conservation value through habitat management and various eco-agricultural practices. However, the conflict between profitable agricultural yield and bird conservation in the area has also been intensifying as reflected by the increasing number of complaints of bird-related crop damage from local farmers in winter.

The study aimed to assess the extent and impact of crop damage caused by birds in Long Valley during winter. The first part of the study involved a transect survey in the area reported to be the most severely affected area of Long Valley to determine the bird diversity and abundance, also the environmental factors of individual farmland plots were collected for analysis of their relationship with bird distribution. The bird species responsible for crop damage (targeted species) were also identified. The second part of the study evaluated the impact of different targeted species by using the technique of focal animal sampling, which involved focused observation of individual bird’s behaviour in the field and to quantify its time budget spent on crop-damaging behaviour. In order to understand the perspectives from farmers, face-to-face interviews with farmers practicing in the area were also conducted.

The study identified five species to have crop-damaging behaviour, which can be further divided into two groups: the crop-consuming species causing actual crop damage included Chinese Bulbul (Pycnonotus sinensis), Crested Myna (Acridotheres cristatellus) and Eurasian Tree Sparrow(Passer montanus). The incidental crop-pecking species causing minimal crop damage included the White Wagtail (Motacilla alba)and Yellow Wagtail (Motacilla tschutschensis). Lettuce (Lactuca sativa) was the only type of crop suffering from bird damage. The intensity of crop-damaging behaviour of a species was estimated by the mean time allocated in crop consumption, and was found to be 66.7%±7.3% in Chinese Bulbul, 31.6%±29.1% in Eurasian Tree Sparrow and 8.9%±12.0% in Crested Myna. However, taking into account of the abundance, distribution and activity record of a species, Crested Myna showed the greatest overall impact to the vegetable crops. Chinese Bulbul showed a relatively focal but intensive damage to a few plots. It was found that having wires and a wet field nearby the plots were significant determinants of the presence of Eurasian Tree Sparrow. And the presence of Chinese Bulbul was significantly associated with the use of bird deterrents. Crested Myna was found in significantly higher numbers in late afternoon and was associated with plots having the seedling stage of lettuce growth.

The study shows that birds do cause localized and patchy damage to vegetable crops in Long Valley. Individual farmlands may exhibit variations in severity of the damage due to the difference in species distribution and environmental factors. The management of bird damage must therefore be individualized from plot to plot. Also education and engagement with local farmers are indispensable to maintaining sustainable agricultural development while conserving avifauna in Long Valley.