By: Dr. Andy Kwarteng
Bar tailed-godwits are known to breed on the Arctic coasts and tundra in Europe and Asia and spend the winters on the coast of tropical and temperate regions including Sultanate of Oman, Australia and New Zealand. From ringing and tracking data, the migration routes of almost all subspecies are well known with the notable exception of the population that winters around the shores of the Arabian Peninsula and Eastern Africa in the West Asia-East Africa shorebird flyway. A survey at the Barr Al Hikman area in January 2016 counted 60,000 bar-tailed godwits and that represents 58–65% of the flyaway population. In this study, 10 female bar-tailed godwits of the subspecies Limosa lapponica taymyrensis wintering at Barr Al Hikman were caught and fitted with 5 gram Solar Platform Transmitter Terminals (PTTs) in November 2015. The main objective was monitor their movements from Argos satellite tracking system to reveal their previously unknown local movements and migration routes, including stopovers and breeding areas. This task was part of The Research Council (TRC) sponsored project on ‘Remote Sensing and Geospatial Data Analysis of Barr Al Hikman Intertidal Ecosystem: Implications of Cascading Predator-prey Effects in a Pristine Seagrass-based Food Web’ by researchers from Sultan Qaboos University and NIOZ Royal Netherlands Institute for Sea Research.
The birds started the northward spring migration in 2016 between February 29 and April 27 and traveled for 7300-8300 km to breedings areas located south of Yamal Peninsula in Siberia, Russia. All the birds used previously unknown staging areas on the east coast of the Caspian Sea or Aral Sea in Kazakhstan during the northward and southward migrations. There was a strong positive relation between the arrival and departure dates in the Caspian Sea and Aral Sea, i.e. birds that arrived late departed late. This probably means that birds faced some constrains in this area, for instance they might need a certain amount of time for fattening up before they could make their final jump to the breeding areas. However, early arriving birds stayed for more days in the area than late arriving birds, indicating that late arriving birds could compensate to some extent for their late arrival. The surviving birds returned to the Barr Al Hikman area between July 28 and August 23. Presently, the PTTs on five birds which have done the migration three years in a row are transmitting data successfully. We lost the five other birds during their migration. The tacking mechanism failed due to the non-functioning or charging of the solar powered tags, or losing the birds due to natural deaths, or to anthropogenic activities. The five birds showed some consistency in their repeat northward and southward migrations routes and the use of the stopovers and staging areas in 2016, 2017 and 2018. In 2017, four individual departed northwards for the spring migration on the same dates as in 2016 but the fourth departed 12 days earlier. The birds were less consistent in their arrival dates at the Caspian Sea and Aral Sea, mainly because most of them migrated faster. The birds departed the staging areas slightly earlier in 2017 compared to the previous year, but did not start breeding earlier. This was mainly because the birds had shorter stopovers between the departure from the Caspian Sea and Aral Sea and arrival at the breeding grounds, supposedly because of a later spring in 2017.
In 2016, the migrations of bar-tailed godwits were recorded by three research groups to monitor the movements of the birds wintering in Mauritania, Oman and northwest Australia. For each study, 10 individuals were fitted with lightweight solar–powered satellite tags. The females tagged in Oman and Mauritania belong to the taymyrensis subspecies whereas those tagged in northwest Australia belong to the menzbieri subspecies. The birds tagged in Oman settled in the central part of Siberia, Russia, with some overlaps with the birds tagged in Mauritania. The group wintering in Australia settled in the northeastern part of Siberia, Russia, with no overlap with the other two groups.
In general, the bar-tailed godwits stay in Barr Al Hikman for about 200 days per year for roosting and foraging on the sabkha and intertidal mudflats. It is therefore safe to conclude that Barr Al Hikman is very important to these birds. The birds have relatively small home ranges in Barr Al Hikman area compared to the staging and breeding areas. We hypothesize that the relatively small home ranges in Barr Al Hikman may be due to better feeding conditions than in the stopover and breeding areas. For the first time, the migration routes, stopovers and breeding areas of the subpopulations of the subspecies Limosa lapponica taymyrensis wintering at Barr Al Hikman have been identified.
By: Dr. Andy Kwarteng is a researcher at the Remote Sensing and GIS Center, Sultan Qaboos University. He can be contacted by email to: kwarteng@squ.edu.om