DOI: 10.5061/dryad.gqnk98ssz
title: Black-tailed Godwit abundancies across key European breeding habitats

description: The endangered continental Black-tailed Godwit (Limosa limosa limosa) is a
 migratory ground-nesting wader breeding in a wide variety of open, wet
 habitats across Europe. Conservation research has concentrated on the
 causes of population decline, but we know surprisingly little about
 whether any resources limit local breeding populations and, if so, whether
 these are resources for the adults or the chicks. We collected data from
 63 key breeding sites in five countries across Europe to test whether,
 after correcting for differences in surveyed areas, the size of Godwit
 breeding populations was related to environmental variables (vegetation
 biomass, soil moisture) or food resources for adult birds (soil
 invertebrates) or chicks (vegetation dwelling arthropods) measured during
 different times of the reproductive cycle. We found the number of Godwit
 territories to be positively related to arthropod abundance during the
 chick-hatching period. We found additional, weaker support for a positive
 relation between Godwit territory numbers and the abundance of
 soil-dwelling invertebrates (mostly earthworms) at clutch laying, but not
 at chick-hatching. These relationships were observed across countries,
 while we found little support for relationships within countries, possibly
 due to the smaller range in conditions that exist within countries. Both
 vegetation growth and soil moisture weren’t related to Godwit territory
 numbers. Our results suggest that food abundance for chicks, and to a
 lesser extent adult birds, are key factors determining the size of local
 Godwit breeding populations. Conservation management aiming to enhance
 local Godwit populations should therefore consider the impacts of
 management strategies on the arthropod prey of chicks.
description: We collected data in 63 sites in France, the Netherlands, Poland,
 Estonia and Finland. All sites were areas potentially hosting breeding
 Godwits, as indicated by survey information from the years before this
 study was conducted. Site selection aimed to include locations varying
 widely in environmental conditions both within countries and between
 countries to incorporate as much variation as possible in variables
 potentially explaining Godwit breeding numbers and representing all
 habitat types used by Godwits for breeding. We investigated how the total
 arthropod and soil-dwelling invertebrate abundance, vegetation biomass and
 soil moisture in two separate periods were related to the number of Godwit
 territories per site. As this gave a better model fit than directly using
 territory densities, we used as the main response variable the number of
 territories while statistically accounting for differences between sites
 in the area surveyed. Additionally, it allowed us to examine whether
 area-territory number relationships differed between countries. Because it
 is unknown if adult Godwits select a breeding area because it confers
 benefits to themselves or to their chicks during the rearing period we ran
 analyses with variable estimates at the estimated clutch-laying and
 chick-hatching dates.