Calidris Canutus Canutus on Taimyr, Siberia

85 DISTRIBUTION, MIGRATIONS AND BIOMETRICS OF KNOTS CALIDRIS CANUTUS CANUTUS ON TAIMYR, SIBERIA PAVEL S. TOMKOVICW & MIKHAIL Y. SOLOVIEV2 Tomkovich P.S. & M.Y. Soloviev 1996. Distribution, migrations and bio metrics of Knots Calidris canutus on Taimyr, Siberia. Ardea 84: 85-98. Studies carried out in northern Taimyr in 1982-84 and 1990-92 were com bined with data from other sources to describe the breeding distribution and densities and the migration of Knots at Taimyr Peninsula, north-central Si beria. Morphometries, recent ring recoveries, dates and directions of mi gration all support the idea that Knots breeding at Taimyr pass through western Europe to winter most probably in Africa. They also confirm the suggestion that Taimyr cannot harbour the entire flyway population and that an unknown breeding area is still to be discovered in Siberia. On the basis of discriminant analyses of linear dimensions formulae to sex Knots were derived; maximum wing length and bill length were the best predic tors. Key words: Calidris canutus - Siberia - Taimyr - population size - migra tion - discriminant analysis lZoological Museum of Moscow State University, Bolshaya Nikitskaya Str. 6,103009 Moscow, Russia, [email protected]; 2Depart ment of Vertebrate Zoology & General Ecology, Biological Faculty, Mos cow State University, 119899 Moscow, Russia. INTRODUCTION more accurate calculations of the population size. In contrast to the established opinion that Si Among long-distant migrant shorebirds, Knots Ca berian Knots are longer billed and shorter winged iidris canutus have attracted much scientific atten than Nearctic (e.e. isiandiea) Knots (a difference tion (e.g. Piersma & Davidson 1992). In spite of used to separate the two populations in winter and this, there is still much that is not known about during migration; Dick et ai. 1976, 1987; Roselaar Knots (Davidson & Piersma 1992a,b). There are no 1983; Prokosch 1988; Davidson et ai. 1986; Schek published data from the Siberian breeding grounds kerman et ai. 1992), recent studies of museum of the nominate subspecies C. e. eanutus, migrating skins revealed similarity in the size of birds from there to its supposed West African winter breeding on Taimyr and those breeding in Green quarters (Dick et ai. 1976, 1987; Davidson & land and northeast Canada (Tomkovich 1990, Piersma 1992b). There is great variation in the 1992). Since this finding might have been biased ways that the breeding range of the Knot at Taimyr by the small samples available in museum collec is depicted (Kozlova 1962; Cramp & Simmons tions, previous conclusions need to be verified 1983; Dick et ai. 1987; Piersma et ai. 1992). A single with larger samples, especially of live-trapped attempt to estimate the size of the Taimyr breeding birds from Taimyr. A substantial sample of sexed population ofKnot was based on umealistic figures Knots captured and measured on Taimyr in 1990 of densities and evaluation of the breeding range 1992 allows us to not only make comparisons (Piersma et ai. 1992). Currently available data al with birds from non-breeding areas, but also ela low us to describe the species breeding range at borate the sexing criteria for Taimyr Knots in the Taimyr more precisely and, consequently, to make hand on the basis of body dimensions. 86 ARDEA 84(1/2), 1996 STUDY AREAS AND FIELD METHODS the forehead, and tarsus length. In 1990-1992 to tal length of bill and head (Green 1980) and in Biometric data of 65 adult Knots were collected 1991-1992 length of middle toe without claw in 1990-1992 in the Gusinaya River valley, 7-10 were also measured. The birds were weighed to km east of Knipovich Bay of the Kara Sea at the nearest 0.5 g with a Pesola spring balance in north central Taimyr (76°05'N, 98°32'E). In addi 1990-92 and with a beam balance in earlier seas tion, measurements of 8 Knots were taken by PST ons. Body masses of egg-laying females were ex during expeditions to the following localities of cluded from analysis. north western Taimyr: Dikson area (73°33'N, Collected birds were sexed by gonadal exami 800 35'E) in 1982-83, lower Lenivaya River nation at dissection. Individually colour-marked (75°l6'N, 89°30'E) in 1983, and Uboinaya River birds that were engaged in territorial defence and mouth (73°37'N, 82°20'E) in 1984. These sites that sang during courtship were identified as ma are all within the Arctic tundra subzone (Chernov les (Whitfield & Brade 1991; pers. obs.). Another 1985), are situated within 20 km from the Kara sexing criterion of captured birds was the breadth Sea shoreline, and are characterized by hilly or of the unfeathered part of the cloaca, perpendicu low mountain landscape (heights up to 200 m lar to the body axis, measured with a ruler to the above sea level) with gentle slopes. The water nearest 0.5 mm (Soloviev & Tomkovich 1995). shed ridges are dominated by polygonal (medal The enlarged bellies of egg-laying females in lion) tundra (Chernov 1985), which is replaced by pairs was used as an additional sexing criterion. If moss tundra and marshes of sedge-grass Carex the sex of a bird was positively identified in one stands at the middle and lower parts of the slopes, of the seasons, the (opposite) sex of their mate(s) respectively. The areas are described in detail el followed from this. The sex of 20 birds among 48 sewhere (Tomkovich and Vronsky 1988a,b; Tom caught and ringed Knots was not identified with kovich & Vronsky 1994; Tomkovich et al. 1994). certainty, even though all Knots with broods are The weather is cold and humid with regular fogs likely to be males (Whitfield & Brade 1991; pers. brought by prevailing northern and northwestern obs. of individually marked birds). winds. Average July air temperature approxima All actively migrating Knots and other flocks ted 4°C. In 1990 and 1991 the timing of snow observed during daily excursions were noted. We melt was normal. In both years low nest predation recorded the number of birds in a flock, their be lead to rather high breeding success. The summer haviour and the direction of flight. All birds in of 1992 was extremely late and cold, with quick transit flight were taken into consideration and we depredation ofall nests by numerous Arctic Foxes can not be certain whether birds carried out local Alopex lagopus. movements or were actively migrating. Forty-eight birds were captured on their nests and with broods with the 'luchock'-trap (Prik Statistical analyses lonsky 1960). Another 25 Knots were collected For most statistical procedures we used Systat throughout the breeding season (9 June to 5 Au 5.0 (Wilkinson 1990), with exception of discrimi gust) and measured before skinning. Wing length nant analysis done in SAS (SAS Institute 1987). was measured (to the nearest 0.5 mm) with a stop The latter was used to work out the best sexing ped ruler in three positions (Svensson 1984): Ull criterion for Knots on the basis of the following flattened wing or minimum chord (wingl), flatte measurements: maximum wing (wing3), bill, to ned but not straightened wing (wing2), and maxi tal head, tarsus and middle toe lengths. Complete mum length - flattened and straightened wing series of measurements were only available for (wing3). The other measurements were taken specimens collected in 1991-92, representing with calipers to the nearest 0.1 mm, and consisted about two-thirds of the total sample. This pre of bill length from bill tip to the feather-line on empted the application of stepwise discriminant Tomkovich & Soloviev: KNOTS ON TAIMYR, SIBERIA 87 80' 90' 100" 110" 120' 130" Fig.1. Breeding distribution of Knots on Taimyr and southerly records of Knots in spring; a (black dots) proved case of breeding (nest and/or chicks found), b (circles) possible breeding (distraction dislays recorded), and c (black triangles) spring records at southern Taimyr and in Central Siberia. analysis on the basis of the complete data set. In Azen 1979). Average probabilities of erroneous an analysis for 31 Knots with all five measure classification were estimated following the formu ments taken, the middle toe length was the first to las of Deev (1977). The probability of misclassifi fall out (see below). Then the stepwise analysis cation was also estimated after applying the discri was used for a subsample of 46 birds for which minant functions to a training sample. measurements of wing, bill, total head and tarsus length were available. We excluded measurements in stepwise analyses after the F -statistic exceeded RESULTS the 0.05 probability level (Ahrens & Lauter 1981). To avoid the loss ofinformation resulting from the Spatial breeding distribution exclusion of birds with less than four measure The data on fauna and status of birds are avai ments, we repeated the discriminant analysis for 1able for more than 110 sites in the Taimyr Penin the best subsets of measurements. The possibility sula. Twenty breeding localities of Knots are of unequal covariance matrices was considered known now in the region (Fig. 1, Table 1). Nest (Davis 1986) and equal prior probabilities to be finds or the presence of unfledged chicks, or long to either sex were used to derive the discrimi fledglings confirm breeding for 18 of these sites. nant functions (Ahrens & Lauter 1981, Afifi & At sites #3 and #20 distraction displays, presuma- 88 ARDEA 84(1/2), 1996 Table 1. Breeding records of the Knot at Taimyr. N- nests, Ch - unfledged chicks, D- distraction displays, B birds with brood patches, Y- badly flying juveniles. Sources are personal communications, unless otherwise stated. Site numbers (#) refer to Fig. 1. # Date Observ.

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