Estimating the size of the Dutch breeding population of Continental Black-tailed Godwits from 2007–2015 using resighting data from spring staging sites

Over the past 50 years, the population of Continental Black-tailed GodwitsLimosa limosa limosa breeding of the East Atlantic Flyway has been in steepdecline. This decline has previously been documented in trend analyses and sixNetherlands-wide count-based population estimates, the last of which wascompleted in 1999. We provide an updated population size estimate anddescribe inter-annual fluctuations in the population between 2007 and 2015. Togenerate these estimates, we integrated a mark-recapture survival analysis withestimates of the densities of colour-marked individuals at migratory staging siteswith known proportions of Continental and Icelandic L. l. islandica Black-tailedGodwits within a Bayesian framework. The use of these analytical techniquesmeans that, in contrast with earlier efforts, our estimates are accompanied withconfidence intervals, allowing us to estimate the population size with knownprecision. Using additional information on the breeding destination of 43 godwitsequipped with satellite transmitters at Iberian staging areas, we found that 87%(75–95% 95% CI) of the nominate subspecies in the East Atlantic Flyway breedin The Netherlands. We estimated that the number of breeding pairs in TheNetherlands has declined from 47,000 (38,000–56,000) pairs in 2007 to 33,000(26,000–41,000) in 2015. Despite a temporary increase in 2010 and 2011, thepopulation declined by an average of 3.7% per year over the entire period from2007–2015, and by 6.3% from 2011–2015. We conclude that investing in anintensive demographic programme at a regional scale, when combined withtargeted resightings of marked individuals elsewhere, can yield population estimatesat the flyway scale