This report provides findings from the first year of a study that has used Movetech ‘GPS-GSM’ tracking devices to track the movements of Lesser Black-backed Gulls from a breeding colony at the Ribble and Alt Estuaries SPA and so investigate their use of the SPA and the Warton Aerodrome. The study had two main objectives: (i) to assess the flight altitudes of adult Lesser Black-backed Gulls from the breeding colony at Banks Marsh in the Ribble and Alt Estuaries SPA during the 2016 breeding season; and (ii) to assess the home ranges of adult Lesser Black-backed Gulls from this colony and their temporal and spatial overlap with the SPA and the area of potential risk of collision with aircraft.

A total of 11 tags were deployed in the 2016 season and usable data received from 10 of these. Birds were caught on the nest using wire mesh traps and fitted with GPS loggers using a permanent wing harness.

Tags were set up specifically to be used to collect data in three dimensions, including flight altitude data. To increase the precision of the GPS altitude measurements, tags were set to stay on for five minutes for each fix, thus allowing time to connect to more satellites.

Movetech tags produced accurate estimates of altitude (generally <2m) once corrections for number of satellites (more than five) and the ellipsoid of the earth had been accounted for. Precision (which we define as two standard deviations from the mean) was 18-26 m therefore being at or a little above that previously recorded elsewhere using different GPS tags. Ground speed was also of little value from the Movetech tags.

Altitude measurements indicated that the majority of flights were at heights of less than 100 m. Birds flew higher during the day-time, although most of their time was still spent at around ground height.

Movetech tags were very appropriate for assessing home range area usage, although with the caveat that fewer data were available to assess night-time area usage. Birds used mainly inland areas, with only a handful of individual trips going offshore. Frequent trips were recorded to the Mersey Estuary as well as further inland to urban areas, fields and landfill sites and ground workings. Locally, birds also frequented the intertidal mudflats and saltmarsh of the Ribble Estuary. Overlap of home ranges with the SPA was greater during the night than during the day. The overlap of home ranges with Warton Aerodrome was small, being less than 3% for both day and night periods for individual birds, and less than 1% for all-birds combined. Temporal overlaps with the Warton aerodrome were also very small – less than 0.5% for all-birds combined across the day and night.

Currently, an alternative system, the University of Amsterdam Bird Tracking System (UvA-BiTS), that requires data download through a fixed base station, offers a better option to the Movetech system used in 2016 for study of flight heights of adult gulls. The UvA-BiTS offers greatest user interface flexibility and fast GPS sampling rates and greater precision in raw data. This recommendation is subject to funding restrictions. Accelerometers may help identify behaviours of birds useful for refining flight height curves, which are tried and tested for UvA-BiTS.