The distribution and phenology of the nominate sub-species of Black-tailed Godwit

D. Kleijn & D. Lammertsma. Alterra, Wageningen UR, The Netherlands.

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Effective conservation depends on how well we know where and when Black-tailed Godwits occur in their flyway. This is crucial information if we want to take conservation measures at the right place and time. Although this information is available in general (e.g. Kuijper et al. 2006, Lourenço & Piersma 2008), much of the detail is lacking. This makes it difficult for conservationists in individual countries to target conservation efforts to the right place and time. In an attempt to address this knowledge gap, a  gap-filling survey of non-breeding Black-tailed Godwit observations was carried out. This survey focussed on the nominate species Limosa limosa limosa. On this website a short overview is given of the main results. A full list with all sites in which Black-tailed Godwits have been observed is given elsewhere on this website. Due to data-ownership issues this information is only accessible to members of the Working Group of the Black-tailed godwit Single Species Action Plan.

Data from existing databases (mainly the International Waterbird Census (IWC) database) were combined with observations in published papers, grey literature and from acknowledged ornithologists throughout the godwit flyway that were contacted by email. Data were collected until August 2012. Black-tailed Godwits were observed in almost 2000 different sites and the total number of observations was 13,331. Although this is an impressive number by itself, it is actually not much considering the large size of the flyway and the fact that a large proportion comes from a small number of North-western European countries.

A number of standard problems with presenting data from unplanned observations apply to the figures presented below. In the next section we briefly discuss the most important ones.

Things to bear in mind when interpreting the distributional and phenological maps and tables

• In certain parts of the year and flyway range, the distribution of the two subspecies overlap and it is generally impossible to reliably separate the two subspecies in the field. Furthermore, the IWC database does not make a distinction between the nominate form L. l. limosa and Icelandic subspecies L. l. islandica. Depending on the time of year, data for the Netherlands, Belgium, France, Spain, Portugal and Morocco include counts of the Icelandic population. Data from Ireland and Great Britain probably exclusively exist of observations of the Icelandic Black-tailed Godwit but, for consistency, we decided to include them nevertheless.
• To a large extent the distributional maps are determined by observational effort. For example, few Black-tailed Godwits were observed in the eastern part of Africa (e.g. Egypt, Soudan, South Soudan, Ethiopia, Kenya). It is unlikely that this area isn’t used by large numbers of staging and wintering Black-tailed Godwits from the Eastern European breeding population. It most likely reflects that not many people have gone looking for this species in that part of the flyway.
• There is a strong bias towards observations around the mid-winter period. Sixty-three per cent of the counts were made in the months December-February. This is largely the result from the large proportion of database originating from the IWC mid-winter count.
• There is large variation in years in which the observations were made. For example, a large proportion of the impressive dataset from Iran was collected in the 1960s and 70’s. We do not know whether the numbers and distribution described by that dataset are representative for the situation today. On the other hand, all data from the Ukraine were collected in 2010.

The data indicate clearly that, outside the breeding season, the Black-tailed Godwit is an aggregative species that tends to concentrate in large numbers in a limited number of sites. More than half of all observations consists of groups of up to 50 Black-tailed Godwits (Fig.1). Nevertheless, sites in which 500 or more Black-tailed Godwits were observed simultaneously accounted for 84% of all observed Black-tailed Godwits suggesting that such are of particular importance. This result is apparently not biased by bird watchers preferentially visiting sites holding the largest number of birds. In Morocco a long-term annual survey is being carried out that covers a large number of sites with a range of apparent suitability for Black-tailed Godwits. The data from these surveys produced a very similar result (Fig. 1). It therefore seems to be a realistic pattern. Table 1 lists the top 20 sites with the highest average number of observations. Many of these sites have been well-known for a long time to be important Black-tailed Godwit staging sites.

Figure 1.
The frequency distribution of the number of Black-tailed Godwits that are observed per site in individual counts. Top-panel, all 1813 sites; bottom panel, just the sites in Morocco, a country with an annual census covering a wide range of habitats.
 

Figure 2. Year round observations of Black-tailed Godwits throughout the flyway.

Figure 2 gives an overview of the year-round observations of Black-tailed Godwits throughout the flyway. The most obvious wintering and staging locations seem to the Iberian Peninsula, the West-African coast and the Sahel zone in the western part of the flyway and the delta of the Tigris and Euphrate rivers, the Iranian Caspian Sea coast in the eastern part of the flyway. Wetlands all along the Mediterranean coast host smaller numbers of Black-tailed godwits, mostly during spring or fall migration (ref figs?). Interestingly, even during the breeding season Black-tailed godwits are being observed in Africa (ref fig?), suggesting that these wetlands are important throughout the year. No separation between the Islandic and nominate subspecies was made because the IWC database did not contain information on the subspecies level. The importance of specific staging and wintering sites is given for the total database and per season. Dots represent the average maximum count /year/site. The top 20 of most important sites are:

Table 1.
The top 20 of the sites with the largest numbers of Black-tailed Godwits. Numbers indicate the between-year average of the within-year maximum of bird observations.

In order to specify the phenology of migration in Black-tailed Godwits histograms are presented per country (average count/year/month).  These figures show the available information on abundance per country and indicate research gaps for specific months and countries. In total 273 specific country-month counts are presented. Half of the data is based on 1 count and showing the strong focus on mid-winter
Figures:

Acknowledgements
Carrying out bird surveys is a time-consuming and therefore costly process. In spite of this many researchers and organizations have freely shared their data, thus making the construction of this dataset possible. We thank Wetlands International, Bernard Trolliet, Eddy Wymenga, Leo Zwarts, Pedro Lourenço, Antoni Marczewski, M. Fasola, Jelena Kralj, T. Mikuska,  Derek Scott, W. Meissner, Tommy Pedersen, Bob Woodcock, Bernhard Walter, Iris Charalambidou, Daan Bos, Imad Cherkaoui and Guy M. Kirwan. We thank Diedert Spijkerboer for obtaining much of the data and collating it into a single database.
We acknowledge http://www.worldbirds.org with databases and contributors to the Ornitorama, Awibaza, and AviCa websites.
Last but not least, we thank the many anonymous birders who took part in the surveys, and without whose efforts many of the data presented here could never have been collected.

This data compilation was sponsored by the Dutch Ministry of Economic Affairs, Agriculture and Innovation (BO-10-001-161).

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