Waterbird surveys were conducted at 12 sites. Sites were chosen to include a range of habitats including soft shore, mangrove and boulder habitats and were divided into Sections A, B, C and D along the Tolo Harbour and Channel; each session there were three sampling locations. Sites were also selected according to their spatial distribution (i.e., avoiding sites which are too close together), accessibility and logistics. Broad site areas included Ting Kok SSSI along the coast of Ting Kok, Shuen Wan, coast of Ma Shi Chau and Tolo Channel. The survey at Yeung Chau was conducted on a P4 sampan around the island.
The sampling protocol was designed to capture all birds using the shoreline habitats as well as mangrove habitat near the shore. Waterbird surveys were conducted using the transect count and point count techniques in accordance with the criteria and guidelines in EIAO Guidance Note 7/2010 and 10/2010. Surveys were conducted in four distinct periods: the wet and dry seasons as well as both the spring and autumn migratory periods. All 12 sites were sampled throughout the wet (June to September) and dry seasons (December to March), while only three sites were sampled, with higher intensity, during the migratory periods. Surveying at each site included a 5-minute point count and a 20 m line transect, where all species observed or heard were recorded. Both point counts and transect surveys were included to optimize data collection. All surveys were conducted at low tide on days when predicted tidal height was lower than 1.20 m above C.D. for more than three hours. This maximized the amount of time and area available for surveys, as well as accounting for variability in the actual tide level from the predicted level.
Transect counts require less time and man-power to survey a given amount of habitat compared to point counts and were therefore used as the main sampling method. The transect length was determined by the maximum length of shoreline at each site. The transect width was extended to 50 m on each side of the line to maximize inclusion of all species and record two habitats at once (soft shore and boulder habitat). The perpendicular distance of the bird from the transect was recorded, and distance sampling methods were used to estimate abundances.
Flight paths of the dominant species and species considered to be of conservation importance were also noted through observing the direction of flight and altitude of birds from the nest or roosting grounds. Photographs of the observed waterbird species were also taken to improve species identification and to ascertain conservation status. This was checked in accordance with the IUCN Red List of Threatened Species (IUCN, 2012), Fellowes et al., (2002), China Red Data Book (Zheng & Wang 1998) and the Key Protected Wildlife Species List (under PRC’s Wild Animal Protection Law). Data on weather conditions were recorded for each survey (both transects and point counts) both descriptively and using a handheld weather station (Osprey Pocket Weather Meter). In addition, data on some environmental parameters including air temperature, relative humidity and total rainfall were obtained from the Hong Kong Observatory website on the day of the survey. This information helped to explain the behaviour or presence/absence of bird species.
Point counts provide a uniform way of recording birds through time. Mangrove point counts were conducted at one site within each section. These point counts were added due to increased detection difficulty for mangrove birds and to assure to include as many species as possible. Point counts covered a 20 m semi-circle within the mangrove habitat and surveys lasted for 30 minutes. Weather condition, bird species and abundance were recorded with 10-minute interval counts.
Additional survey: boat survey
Boat surveys were conducted by using a fishing boat travelling in a transect across the four sections in the Tolo Harbour and Channel at a constant low speed (5 knots). The aim of these surveys was to record species that utilize open water and which cannot be surveyed during regular shore counts. Helpers with bird watching experience were recruited for the survey. Each surveyor was required to survey one side of the boat, left or right. All birds encountered within both side of the transect were recorded to maximize the bird diversity recorded in the Tolo area.