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Studying the ecology of Red Knots Calidris canutus and Bar-tailed Godwits Limosa lapponica by individual colour-ringing  (Updated November 2009)

 

In 1998 the shorebird-group of the department of Marine Ecology of the Royal Netherlands Institute for Sea Research (NIOZ) on Texel, started a colour-ringing project on Red Knots. In spring 2001, this project was extended with a second species, the Bar-tailed Godwit. Individuals of these species are caught with mist nets or other devices and provided with a unique combination of colour-rings to enable individual recognition. Here, the ‘why’ and ‘how’ of these projects will be further explained and the current state of affairs is given.  

            In Northwest Europe, two populations of the Red Knot and also two populations of the Bar-tailed Godwit occur. In the non-breeding season the population of Red Knots breeding in Greenland and Northeast Canada (Calidris canutus islandica) stages in the coastal areas of Northwest Europe. The Wadden Sea is one of their important wintering areas. The other population of Knots (Calidris canutus canutus) breeds in Northern Siberia and winters mainly along the shores of West-Africa. These birds use the Wadden Sea only as a fuelling station from the end of July till the beginning of September, before they head off  to their wintering quarters, and during May, just before the migration to the breeding area. In May these birds concentrate mainly in the Schleswig Holstein part of the Wadden Sea.

            For the Bar-tailed Godwit, the situation is comparable. The population breeding in Northern Scandinavia and around the White Sea, Limosa lapponica lapponica, winters along the shores of Western Europe, including the Wadden Sea. The other population, Limosa lapponica taymyrensis, breeds mainly in the southern parts of the Yamal and Taymyr peninsulas in Northern Siberia and occurs only in Western Europe during migration to and from the wintering areas in West-Africa. Also for this population, the Wadden Sea is an indispensable fuelling station in May and August-September, when birds migrate the long distance between summer and winter quarters.

 

The purpose of this project

The tool of individual colour-marking enables us to answer a set of ecological questions that cannot be answered otherwise, like the annual mortality and survival of the different populations. We will try to relate possible differences in survival between populations and/or years to, for example, conditions in the breeding area (e.g. weather, abundance of predators), in the wintering-areas (e.g. weather, food availability) or during migration (e.g. weather, migration distance). In addition, we would like to know how individual Red Knots and Bar-tailed Godwits utilize the feeding and resting areas in the Wadden Sea. Are birds site-faithful, within a year and between the years respectively, and, if they are, on which scale? Are there individual differences in prey-choice? Are the Bar-tailed Godwits that forage on leather-jackets in May on the inland pastures of  the Wadden Sea area the same individuals each year? What is the turnover-rate within a certain staging area? Are there intra-specific differences in habitat use and/or foraging behaviour between individuals from different populations using the Wadden Sea during the same period of the year, in May or August for instance? Finally we aim to estimate population-sizes of the different populations of Red Knots and Bar-tailed Godwits by determining the densities of colour-ringed birds in the field.

 

 

How do we work?

We cooperate with a number of Dutch bird-ringing groups: VRS Calidris on Schiermonnikoog (Red Knots and Bar-tailed Godwits), VRS Castricum and VRS Franeker (only Bar-tailed Godwits) and a French ringing group in Moëze-Olèron along the Atlantic coast (only Knots). Red Knots are caught almost exclusively by mistnetting (Figure 1). Only around the period of the new moon, the nights are sufficiently dark for successful mistnetting. Bar-tailed Godwits can be caught with mistnets, but a clap-net or a so-called “wilsternet” is also used. On the “Vinkenbaan Castricum” migrating Bar-tailed Godwits are lured to the ground by playing their sound and subsequently caught with a clap-net. Using the “wilsternet-method”, birds flying around are attracted with sound, decoys and sometimes a living decoy. During landing the birds are then caught with a kind of clap-net. This traditional catching method was in the past mainly used to catch Golden Plovers (“wilsters”) for consumption.

 

Figure 1. A section of mistnets on the mudflats of “De Richel” near Vlieland, prepared to catch Knots at rising tide during the night.

 

            Every Red Knot or Bar-tailed Godwit is marked individually with four colour-rings, combined with one yellow, red, green or lime flag and a metal ring. We only use white or lime, blue or green, red and yellow colour-rings. In case a green flag is used, green colour-rings are used instead of blue. In combination with a lime flag, lime colour-rings are used instead of white. There are always two colour-rings on the left and two on the right tarsus. The metal ring is always on one of the tibiae, but it is not part of the code. The yellow, red, green or lime flag is the marker of our scheme and can be on the tarsus as well as on the tibia on 8 different positions (see appendix 1). In case the flag is on the tibia, the metal ring is on the opposite site. If the flag is on the tarsus, its position with respect to the colour-rings is of importance: it can be above, in between, or below the two colour-rings (appendix 1).

Using 4 colour-rings on 4 positions makes 4⁴  = 256 different combinations. With the 8 different flag positions we end up with 8 x 256 = 2048 combinations per flag colour.

Biometrics and moult phase are recorded of all Red Knots and Bar-tailed Godwits we catch. We also collect a drop of blood of each bird to be able to determine sex afterwards (DNA-analysis). In Bar-tailed Godwits, however, it is in most cases possible to distinguish between the sexes on the basis of bill-length and/or plumage.

 

Figure 2. The colour-rings and flags we use for the Red Knots and Bar-tailed Godwits.

 

Figure 3. The NIOZ-vessel “Navicula”, standing clear of the water on the mudflats near De Richel. This ship is used for most of our catching activities in the Wadden Sea.

 

The state of affairs, the Red Knot

            From 1998 to November 2009 we colour-ringed 6,784 Knots in total; 3,011 in the western part of the Dutch Wadden Sea, mainly at “De Richel” (53.17 N, 5.08 E) and the small island of Griend, 1,578 in the eastern part of the Wadden Sea (on Schiermonnikoog en Simonszand), 1,620 near Iwik on the Banc d’Arguin in Mauritania, 407 along the Atlantic coast of France, 134 in the Schleswig-Holstein part of the German Wadden Sea and 13 on the breeding grounds in Greenland.

            We caught 57% of our Knots in late summer and autumn (July–October), 30% in winter (November–February) and 13% in spring. We estimate the ratio between the subspecies islandica / canutus  in our catches to be about 3:1. Unfortunately we are not able to determine the subspecies of a small fraction of the birds we catch in late summer in the Wadden Sea.

            Till November 2009, we received in total 12,972 resightings of 3,496 different individuals (52% of the total number of birds marked). The maximum number of observations of a single individual is 95, however, 40% of the birds (1,389 individuals) was seen only once. The observations were made by 292 different observers. Our best observer, Laurens van Kooten on Texel, did 1,916 individual observations! Most observations were done in the western part of the Dutch Wadden Sea (3,938). In the eastern part of the latter area 554 observations were done as well as 108 along the Dutch West coast and 18 in the Dutch Delta area. Outside the Netherlands, 7,115 individual observations were done on the Banc d’Arguin in Mauritania, 198 in Great Britain (Figure 4), 544 in Schleswig Holstein, 129 on Iceland, 191 in Norway, 69 in France, 17 in Sweden, 14 in Greenland, 15 in Spain, 2 in Canada and 24 in Ireland.

 

 

Figure 4. Red Knot R3WYBW, caught on 1 August 2003 at “De Richel”, a sandbank just Southeast of Vlieland, Netherlands. This picture was taken on 25 January 2004 by Adrian Winter near Heysham, Lancashire (Northwest England).

 

 

 

The state of affairs, the Bar-tailed Godwit

Between spring 2001 and November 2009, 3,432 Bar-tailed Godwits were colour-ringed. Most birds, 1,778 (= 52%), were caught in the Western part of the Dutch Wadden Sea, mainly on Terschelling and Texel. At the “Vinkebaan Castricum” (53.32 N, 4.37 E) 653 (= 19%) birds were caught, in the eastern part of the Dutch Wadden Sea 697 (= 20%) and 48 in the Wadden Sea of Schleswig Holstein. During November en December 2002 – 2008 we also colour-ringed 248 Bar-tailed Godwits near the village of Iwik on the Banc d’Arguin in Mauritania. Most birds were caught in spring: 28 in March, 294 in April and 2438 in May. Smaller numbers were caught in July (75), August (128), September (96) and October (84). Because the majority of the birds was caught in May and concerns individuals on northward migration from the African wintering grounds, far more birds from the latter population (L.l. taymyrensis) were marked than birds from the population wintering in Europe (L.l.lapponica). 

Until now we received 10,627 resightings of 1,821 different individuals (53% of the total number of birds marked). The resightings were done by 303 different observers. 35 observers did 20 or more resightings. Our best observer, Harry Horn from Terschelling, even did 4,009 observations! Most resightings come from the Dutch Wadden Sea area (9,528). From the Dutch mainland coast we received 26 observations and 13 from the Dutch Delta area. On the Banc d’Arguin in Mauritania, 778 resightings were done. Moreover, we received individual observations from Spain (34), France (34), England (30), Schleswig Holstein (81), Ireland (12), Belgium (2), Finland (6), Norway (4), Poland (1), Denmark (8) Sweden (17), Senegal (3, see Figure 5), The Gambia (1) and the furthest resightings come from Namibia (14).

 

Figure 5. Bar-tailed Godwit  Y1BYRR was caught on 19 May 2001 near Den Hoorn on Texel. This picture was taken by Didier Vangeluwe on 13 January 2002 in the Delta du Saloum in Senegal.

 

For the observers

Anybody who has seen a Red Knot or a Bar-tailed Godwit with a yellow, red, green or lime flag and colour-rings is requested to send us this observation, including position of rings and flag, colour of the flag, geographical location (if possible also the latitude and longitude of the place) and date. Please indicate, per leg-position, which rings you saw. For instance: left tibia: no rings, left tarsus: red over white, right tibia: yellow flag, right tarsus: yellow over blue (in our code we call this bird: Y2RWYB, see Appendix 1). Observers will get information on the date and place of ringing, including the other observations of the bird(s). We are also very interested in additional information such as:

-       The type of the area where the bird was observed (at a high tide roost or at the feeding area).

-       The size of the flock in which the bird was seen.

-       The number of birds that could be checked for colour-rings.

-       The extent of breeding plumage of the bird.

Observations of Red Knots or Bar-tailed Godwits with a yellow, red, green or lime flag of which the colour of the rings could not be determined are of importance nevertheless, especially in combination with the total number of birds that could be controlled for colour-rings. 

 

Please send your observations to:

 

NIOZ Shorebird-group, Bernard Spaans

Postbus 59

1790 AB Den Burg, Texel

The Netherlands

Phone +31 222-369490

Or, preferably, by e-mail: shorebirds@nioz.nl

 

Figure 6.  A Red Knot caught in a mistnet

 

Figure 7. Red Knot R6RRYY on the beach near Iwik on the Banc d’Arguin in Mauritania.

 

 

Figuur 8. Bar-tailed Godwit Y7YWRB on the Banc d’Arguin in Mauritania.

 

 

 

Appendix 1. Colour-ringing scheme for Knots and Bar-tailed Godwit as used by the NIOZ. Cr: colour-ring.

Code: colour of flag (Y, R, G or L), followed by position of flag (1-8), first, second, third and fourth colour-ring. Colours used are: Yellow, Red, White or Lime, Blue or Green.

 

Flag-position		Left	Right
1	Tibia	Flag	metal
	Tarsus	First     Cr Second Cr	Third   Cr Fourth Cr
2	Tibia	metal	Flag
	Tarsus	First     Cr Second Cr	Third   Cr Fourth Cr
3	Tibia		metal
	Tarsus	Flag First     Cr Second Cr	Third   Cr Fourth Cr
4	Tibia		metal
	Tarsus	First     Cr Second Cr	Flag Third   Cr Fourth Cr
5	Tibia		metal
	Tarsus	First     Cr Flag Second Cr	Third   Cr Fourth Cr
6	Tibia		metal
	Tarsus	First     Cr Second Cr	Third   Cr Flag Fourth Cr
7	Tibia		metal
	Tarsus	First     Cr Second Cr Flag	Third   Cr Fourth Cr
8	Tibia		metal
	Tarsus	First     Cr Second Cr	Third   Cr Fourth Cr Flag

 

 

 

Publications in which results of this colour-ring project are used

 

Kraan, C., J.A. van Gils, B. Spaans, A. Dekinga, A.I. Bijleveld, M. van Roomen, R. Kleefstra & T. Piersma 2009. Landscape-scale experiment demonstrates that Wadden Sea intertidal flats are used to capacity by molluscivore migrant shorebirds. Journal of Animal Ecology 78,

 

Spaans B., M. Brugge, A. Dekinga, H. Horn, L. van Kooten & T. Piersma 2009. Oost west, thuis best? Op welke schaal benutten individuele Kanoeten het Nederlandse Waddengebied. Submitted to Limosa, accepted in 2009.

 

Spaans, B., L. van Kooten, J.S.M. Cremer, J. Leyrer & T. Piersma. Densities of individually marked migrants away from the marking site to estimate population sizes: a test with three wader populations. Submitted in 2008.

 

Duijns, S., J.G.B. van Dijk, B. Spaans, J. Jukema, W.F. de Boer & T. Piersma 2009. Foraging site selection of two subspecies of Bar-tailed Godwit Limosa lapponica during northward migration; time minimizers accept greater predation danger than energy minimizers. Ardea 97(1): 51-59.

 

Van den Hout, P.J., B. Spaans & T. Piersma 2008. Differential mortality of wintering shorebirds on the Banc d’Arguin, Mauritania, due to predation by large falcons. Ibis (2008),150 (Suppl. 1): 219-230

 

Leyrer, J., Spaans, B., Camara, M. & Piersma, T. 2006. Small home ranges and high site fidelity in red knots (calidris c. canutus) wintering on the Banc d’Arguin, Mauritania. J. Ornithol 147 (2): 376-384.

 

Van Gils, J.A., Piersma, T., Dekinga, A., Spaans, B. & Kraan C. 2006. Shellfish dredging pushes a flexible avian top predator out of a marine protected area. Plos Biol. 4: e376.

 

Spaans, B. Survival and behaviour in shorebirds wintering on the Banc d’Arguin, Mauritania. Progress-report 2002 – 2005. Nioz-report 2006-1.

 

Reneerkens J. Piersma T. & Spaans B. 2005. De Waddenzee als kruispunt van vogeltrekwegen. Literatuurstudie naar de kansen en bedreigingen van wadvogels in internationaal perspectief. Nioz-report 2005-4.

 

Piersma , T. & Spaans, B. 2004. The power of comparison: ecological studies on waders worldwide. Limosa 77: 43-54.

 

Brochard, C., Spaans, B., Prop, J., & Piersma, T. (2003). Use of individual colour-ringing to estimate annual survival in male and female Red Knot Calidris canutus islandica: a progress report for 1998-2001. Wader Study Group Bulletin, 99, 54-56.

 

Spaans, B. (2000). Wat doet de kanoet? Ecologisch onderzoek met behulp van individueel herkenbare vogels. Graspieper, 20, 106-110.