Phenology, stopover dynamics and population size of migrating Black-tailed Godwits Limosa limosa limosa in Portuguese rice plantations

摘要

Between 2005/06 and 2008/09 we studied Black-tailed Godwits Limosa I. limosa staging in the rice fields surrounding the Tejo and Sado estuaries, Portugal. Godwits were counted weekly and flocks were scanned for colour-ringed individuals. We analysed phenology, dynamics of the stopover, and esti-mated the size of the Portuguese staging population as well as the total west-ern limosa population. Godwits started arriving in January. Numbers peaked in the second half of February, after which they quickly departed from the area. Comparison with previous records suggested that numbers have decreased since the early 1990s, and that godwits currently peak later than some 15 years ago. Individual staging durations averaged 22.6 days in 2007 and 25.3 days in 2009, and increased towards the end of the staging period. We estimated that a total 59 200 birds used the area in 2007 and 53 100 in 2009. Using estimates for the proportion of colour-ringed birds in the flocks, we estimated the popula-tion size of the western part of the L. I. limosa population at 133 151-140 722 birds. This is higher than previous estimates based on inventories of the breed-ing population, but accounts for the non-breeding segment of the population. Thus, we estimate that 38-44% of the NW European Black-tailed Godwit popu-lation stage in Portugal. It is argued that processes in Iberia are not likely to have contributed to the population decline as the area for rice cultivation has in-creased. Nevertheless, as godwits staging in Iberia are totally dependent on human-made habitats, changes in rice farming practices could have great im-pact on the total population size.