Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://vertebrata.bio.msu.ru/Curlew_Sandpipers_Calidris_ferruginea_on_their_breeding_grounds.pdf Äàòà èçìåíåíèÿ: Mon Feb 8 19:41:24 2010 Äàòà èíäåêñèðîâàíèÿ: Mon Oct 1 19:41:22 2012 Êîäèðîâêà:

Tomkovich & Soloviev: Schedule and geographic distribution on the breeding grounds

19

Curlew Sandpipers Calidris ferruginea on their breeding grounds: schedule and geographic distribution in the light of their breeding system
P.S. TOMKOVICH1 & M.Y. SOLOVIEV2
1

Zoological Museum, Moscow Lomonosov State Univ., Bol. Nikitskaya Street 6, Moscow 125009, Russia 2Department of Vertebrate Zoology, Biological Faculty, Moscow Lomonosov State Univ., Moscow 119992, Russia

Tomkovich, P.S. & Soloviev, M.Y. 2006. Curlew Sandpipers Calidris ferruginea on their breeding grounds: schedule and geographic distribution in the light of their breeding system. International Wader Studies 19: 19­26. Curlew Sandpipers arrive on their breeding grounds in the tundra already paired, and arriving birds distribute themselves over the southern parts of the breeding range according to available snow-free habitats. Site fidelity is low between years and numbers at single sites fluctuate widely. New arrivals tend to settle close to early pairs. After egg-laying, as snowmelt and predation on clutches develop, most males, and females with failed nests move farther north in Taimyr for a new breeding attempt where the environment corresponds to an earlier stage of spring in the south. These birds form a second breeding wave. Males leave the breeding grounds by early July; if breeding fails females leave soon afterwards; in successful breeding years they depart in late July­ early August. Most juveniles leave in early August. The paper discusses the key features of the Curlew Sandpiper breeding system, and presents a model to explain the peculiar breeding population structure and breeding schedule of this species, for example the bimodal pattern of clutch completion. INTRODUCTION The Curlew Sandpiper Calidris ferruginea is a Palearctic breeding species which has attracted increasing interest from ornithologists in recent decades. After some debate (Birula in Pleske 1928, Portenko 1959, Kozlova 1962, Pitelka et al. 1974, Leonovich & Veprintsev 1980, Kondratyev 1982), polygeny has become generally recognised as the species' breeding system (Pitelka et al. 1974, Tomkovich 1988). Certain features of species morphology indicate that polygeny in the Curlew Sandpiper probably developed only recently from monogamy, and it has some peculiar features along with related breeding biology (Tomkovich 1988). As yet, there is no comprehensive interpretation of such peculiarities as the bimodal distribution of clutch completion and hatching dates (Tomkovich et al. 1994, Schekkerman & van Roomen 1995), or the large fluctuations in species numbers on some breeding grounds (e.g. Tomkovich et al. 1994, HÆtker 1995, Tulp et al. 2000). This study aims to relate breeding schedule and numbers of Curlew Sandpipers at different sites to the species' breeding system. THE FEATURES OF SPECIES BIOLOGY RELATED TO POLYGENY AND POPULATION STRUCTURE The following peculiarities of species biology aid understanding of variations in breeding schedule and numbers of Curlew Sandpiper. Arrival of paired birds On arrival in June (Table 1), it was found that many Curlew Sandpipers migrate within the breeding range or arrive at their breeding sites already paired (Sdobnikov 1959, Priklonski et al. 1962, Kondratyev 1982, Tomkovich 1988a,b, Frodin et al. 1994b, Tomkovich et al. 1994, HÆtker
19

1995). Annual variation in the fraction of birds paired on migration is possible. Thus, during the active start of migration, just after a sharp warming up of weather on 10 June 1982 at Dickson, north-western Taimyr, Curlew Sandpipers were passing in flocks of up to 18 birds. Fighting among birds in flocks was observed after landing. Pairs (some were migrants) appeared only on the next day (Tomkovich & Vronski 1988b). During 17 years of studies in the breeding range of the Curlew Sandpiper, we have never again seen flocks that large on active migration in the Siberian Arctic. Contrary to this observation, 85% of birds recorded on active migration were already in pairs late in the season of 1992 in north-central Taimyr (Tomkovich et al. 1994). Low site fidelity A low return rate was found in two of several studies where ringing of breeding Curlew Sandpipers was involved (Spiekman & Groen 1993, Underhill et al. 1993, Tomkovich & Soloviev 1994, Tulp & Schekkerman 2001). Site fidelity has been shown by adult females only. In a single study where territorial males had been ringed, none of them returned the next year (Tomkovich & Soloviev 1994). Large fluctuations of breeding density Irregular breeding of Curlew Sandpipers is found in some areas of the species' breeding range (Holmes & Pitelka 1964, Kondratiev 1982, HÆtker 1995, V.K. Ryabitsev pers. comm.). This feature was used to recognise peripheral areas of the species' breeding range versus core areas where the species breeds regularly (Lappo 1996, Lappo & Tomkovich 2006). In recent years, large fluctuations in breeding densities were recorded for several sites of both core and peripheral areas (Table 2; see also Tulp et al. 2000). In 1983, the largest local breeding density (32.1 nests/km2) was recorded for Curlew Sandpiper on the lower Lenivaya River (75°16'N, 89°30'E),


20

International Wader Studies 19

northern Taimyr, where nine females were nesting on a plot of 28 ha (Tomkovich & Vronski 1988a). Density on smalland large-scale study plots varied depending on time of localized and general thaw. Thus, Curlew Sandpipers bred in the southern tundra subzone only in seasons with a late spring and a cold summer (Haviland 1915, HÆtker 1995, Lappo 1996), while species' densities in high-Arctic areas were lowest in extremely cold seasons (1992 and 1994; Table 2). Sex ratio Only a few estimates of sex ratio for breeding Curlew Sandpipers are available (Table 3). In two of these cases, when bird distribution was mapped early on small areas already occupied by Curlew Sandpipers, the ratio of males and females was about equal with all males paired. Mapping on a large plot established independently of bird distribution gave a different result: males outnumbered females by 2­10

times. Males were more numerous than breeding females also in the Pyasina Delta in 1990 (H. HÆtker in litt.) and at Medusa Bay in 1997 (Khomenko et al. 1999). These limited data imply that the sex ratio is generally skewed to males; nowhere have females outnumbered males, as can be expected in a polygenous species. Pair bonds A number of authors stated that pair bonds in the Curlew Sandpiper last for two, three or more weeks in a season (e.g. Holmes & Pitelka 1964). Our data indicate pronounced variation among sites and individuals; available information does not allow formal statistical interpretation. Females start to chase off their mates after laying a second or third egg of a clutch. At some of our study sites on Taimyr and in the Kolyuchin Gulf, Chukotsky Peninsula, males left territories immediately or soon after the onset of incubation by females.

Table 1. Arrival and northward migration of Curlew Sandpiper in the breeding sector of Arctic based on literature sources. Region Range of first records Outliers
1

Pronounced migration

Last records

No. of observations: years & sites 6 28 23 9 3

Yamal Peninsula Taimyr Peninsula Northern Yakutia Chukotka Alaska
1

4­11.06 3­14.06 25.05­8.06 25.05­6.06 5­8.06

29.05 31.05, 1.06 20.05 ­ ­

8­14.06 4­23.06 27.05­11.06 ­ ­

­ 22.06­2.07 8­12.06 ­ ­

­ Records several days before further regular observations were considered as outliers. Table 2. Curlew Sandpiper breeding density (nests per 1 km2) fluctuations based on multi-year plot studies. Site & latitude Yamal Peninsula Yaibari, 71°04'N Year Plot size (km2) Density Source

1988 1989 1990 1991 1992 1993 1994 1995 1990 1991 1992 1990 1994 1991 1992 1994 1996 1997 2000 2001 1994 1995 1996 1997 1998 1999 2000 2001 2002

3 3 3 3 3 3 3 3 1 1 1 19.8 12 14 15.6 7.5 4 12 4 4 1.26 1.26 1.26 1.26 1.26/0.5* 1.26/0.5* 1.26/0.5* 1.26/0.5* 1.26/0.5*

1.0­1.66 1.0­1.66 0.33­0.67 0.0­0.33 0.0 6.0 0.0 0.0 17 4 3 2.3 0.58 2.21­2.36 min 1.28 4 18 max 2.1 2.25 3.75 1.59 2.38 0.79 1.59 0.0/6.0 0.79/6.0 0.79/2.0 0.0/0.0 0.0/6.0

R R R R R R R R

yabitsev yabitsev yabitsev yabitsev yabitsev yabitsev yabitsev yabitsev

pers. pers. pers. pers. pers. pers. pers. pers.

comm. comm. comm. comm. comm. comm. comm. comm.

Taimyr Peninsula Knipovich Bay, 76°05'N

Tomkovich et al. 1994

Cape Sterlegov, 75°25'N Pronchischev Lake, 75°16'N Medusa Bay, 73°13'N

Bludnaya R., 72°51'N

HÆtker 1995 Tulp et al. 1998 Schekkerman & van Romen 1995 Spiekman & Groen 1993 Hertzler & GÝnter 1994 Tulp et al. 1997 Khomenko et al. 1999 Kharitonov 2002 Kharitonov 2002 Soloviev et al. 2003 Soloviev et al. 2003 Soloviev et al. 2003 Soloviev et al. 2003 Soloviev et al. 2003 Soloviev et al. 2003 Soloviev et al. 2003 Soloviev et al. 2003 Soloviev et al. 2003

* two plots in different habitats


Tomkovich & Soloviev: Schedule and geographic distribution on the breeding grounds Table 3. Sex ratio on different study plots/years on Taimyr. Study area and latitude Year Study plot size (ha) Number of males Knipovich Bay, 76°05'N 1990 1991 1992 1983 1984 1989 1997 100 100 100 28 45 700 125 300 31 14 7 8 7 10 7 16 females 17 4 3 9 9 1 6 6 Source

21

Tomkovich & Soloviev 1994; Tomkovich et al. 1994 Tomkovich & Vronski 1988 Tomkovich 1988, unpubl. HÆtker 1995 S. Khomenko, in litt S. Khomenko, in litt

Lenivaya R., 75°16'N Uboinaya R., 73°37'N Malaya Logata R., 73°23'N Medusa Bay 73°20'N

This was recently supported by Tulp & Schekkerman (2001) for north-western Taimyr. In localities where male territories formed dense clusters in the best habitats, territory defence and courtship of females by males continued sometimes up to southward departure. These territorial males provided some protection to their incubating females against constant chasing by other males during the females' feeding bouts. Paired territorial males in territory clusters ceased territory defence only after predation of a female's nest or termination of the pairing season. The latest territorial males in a season were always associated with active nests (Tomkovich 1988). Thus, taking male association with a pre-nesting and incubating female as a pair bond, the bond can last for c.8­25 days in this species. Migratory drift during the nesting period Several indications exist of migratory drift during the nesting period, at least on Taimyr where most of our observations were made. a) In 1982, in the Dickson area, where rocky, dry tundra ridges are a characteristic feature of the landscape, we found that the number of territorial males decreased instantly after a quick snowmelt. Mostly nesting females and some associated males remained in the area during 20­29 June. At the same time, post-breeding flocks of inactive Curlew Sandpipers were not recorded. A similar pattern was reported by Tulp & Schekkerman (2001) for 2001 in Medusa Bay, to the south of Dickson. In that early and warm season, males left soon after clutch completion which occurred 13­29 June. However, subdued migration continued for about a week after termination of the main arrival period at the beginning of the third week of June. b) In 1984, a year of high predation pressure (Tomkovich 1995b), new females appeared during June on the study plot in the Uboinaya River area, allowing successive polygeny in some males. However, neither the female (including colourmarked birds) nor the male were ever seen again at a territory if a nest was depredated (Tomkovich 1988a), which happened regularly after 24 June. This indicates departure of failed breeders, which is supported by visible migration of single pairs eastward along the coastline on 21 and 27­29 June of that year. c) Disappearance of breeding males and females (including colour-marked birds) was recorded in cases of nest depredation in the last week of June 1983 on the lower Lenivaya River. However, gently sloping landscape and late snowmelt allowed sustained appearance of new territorial males during June in areas with suitable habitats and a mosaic of snow and snow-free patches.

d) In the Knipovich Bay area, the number of territorial males grew during June, both in 1990 and 1991. Mapping of territorial males showed an increase from three pairs on 12 June to 18 males on 19 June, and reached the maximum of 31 males/km2 on 27 June in 1990 (Table 3). Similarly, in 1991, male numbers increased towards the end of June from nine birds on 21 June to 14 on 28 June. One of several territorial males ringed in late June 1991 was seen two days later displaying at a distance of 0.5 km from his former territory. e) The same was observed in the Medusa Bay area in 1998 in a prolonged and cold spring season: 12 male territories were recorded on a plot of 4 km2 on 14 June, and 27 territories on 20 June (R. Felix & C. van Turnhout in litt.) These observations show that, at least in favourable seasons, numbers of territorial Curlew Sandpiper males decrease during the breeding season in southern parts of the species' breeding range at Taimyr, and increase farther north, indicating gradual movement of a portion of the population northward within this part of the breeding range. Observations supporting disappearance of Curlew Sandpipers from southern breeding areas in mid-June, once nesting had commenced, are also noted for the Indigirka River delta, Yakutia (J. Pearce in litt.). Re-nesting (replacement clutches) Disappearance of ringed females from study areas after clutch predation made it impossible to directly prove re-nesting in the Curlew Sandpiper. Nevertheless, brood-patches on female underparts are good indicators of nesting status. Falling out of feathers and skin vascularization of brood-patches develop during the egg-laying period (pers. obs.). Therefore, females with large non-vascularized brood-patches during the nesting period can be safely categorized as failed breeders, because vascularization in waders decreases in a few days without incubation. Among five egg-laying Curlew Sandpiper females collected on Taimyr in 1982­1991, all three birds of 17­19 June had their brood-patches at a developing stage, while two birds of 28 June 1990 and 10 July 1983 had well-developed, inactive brood-patches. Thus, there are some grounds to conclude that females laying in the second half of the nesting period are laying their replacement clutch. More data are needed to learn details of timing and regularity of re-nesting; however, re-nesting is unlikely in the most unfavourable seasons, such as 1992 (a female collected from a pair on 25 June 1992 had a well-developed ovarium, but had not laid her eggs yet). Curlew Sandpipers supposedly did not produce replacement clutches in the Medusa Bay area, north-western Taimyr, in 2000 and 2001 (Tulp et al. 2000, Tulp & Schekkerman 2001).


22

International Wader Studies 19

Broad distribution through non-breeding areas Ring recoveries and sight records of colour-marked birds have shown that Curlew Sandpipers from some parts of the breeding range fan out to several flyways across Eurasia (Underhill 1995, Minton 1998, Tomkovich et al. 2000). In this view, Taimyr is a prominent area having Curlew Sandpiper recovery links with Europe, Africa, south Asia and Australia. Nevertheless, most movement records link the Taimyr Curlew Sandpipers with Europe (Tomkovich et al. 2000), while Yakutia to the east provided mostly records of Australian marked birds (Underhill 1995, Minton 1998, papers in this volume). At the same time, there is only one record of exchange between nearby flyways on non-breeding grounds until now (Minton 1998, interpreted in Tomkovich et al. 2000). Therefore, based on currently available information, it is difficult to believe with Minton (1996) that an Australian banded Curlew Sandpiper will be recorded in South Africa (or vice versa). MIGRATION AND BREEDING SCHEDULE Few features of Curlew Sandpiper migrations in the Arctic are known due to scarcity of published observations and prevalence among them of general faunistic data. Few studies specifically focused on Curlew Sandpiper migration (Frodin et al. 1994 a,b, Tomkovich et al. 1994, HÆtker 1995). Below we discuss migration patterns for the tundra area, encompassing the species' breeding range between the Urals and Alaska. Arrival Information about first arrivals is most common (Table 1). Large among-year variation occurs due to varying snow and weather conditions at arrival time (Tomkovich et al. 1994). Nevertheless, even in late seasons, small numbers of Curlew Sandpipers may arrive early, encountering a winter-like environment with almost no snow-free patches (Kretchmar & Leonovich 1965, Tomkovich et al. 1994). Birds arrive at the northern parts of the species' breeding range several days later, compared to southern localities of the same region. Thus, the earliest species record date is 6 June for northern coastal Taimyr (Tomkovich & Vronski 1994, Tomkovich et al. 1994), 8 June for New Siberian Islands, Yakutia (Rutilevski 1958, 1963), and 3 June for Wrangel Island (Stishov et al. 1991); these dates are later than the earliest arrival dates for the southern parts of their respective regions (Table 1). Arrival/migration schedule differs by about one week between western and eastern parts of the species' breeding range (Table 1), that is, events develop earlier in Yakutia and Chukotka (east) than in Yamal and Taimyr (west). Little information is available on the termination of arrival, apart from data from several sites where Curlew Sandpipers normally do not breed, and therefore disappearance of migrants is obvious. However, a likely drift of Curlew Sandpipers in the direction of their northward migration continues till about the end of June (Taimyr; see above). Breeding The most comprehensive data on the species' breeding schedule were collected on Taimyr (Tomkovich et al. 1994, HÆtker 1995, Schekkerman & van Roomen 1995, Tulp et al. 1997, 2000). Assuming that egg-laying normally occurs over three days, and incubation lasts for 20.4 days on average

(Tomkovich et al. 1994, Tulp et al. 1997), it is possible to compile information from these studies (Fig. 1) and compare it with that from other sources. Curlew Sandpiper has a highly variable length of egglaying season, both among years and among sites (Fig. 1). The period required for clutch completion in local populations varied from nine to 31 days in a site/season, being the longest in the northernmost areas during good breeding conditions, while periods were shorter in northern areas if the season was characterised by late snow melting (e.g. 1992) and possibly in more southerly areas. Distribution of egg-laying and hatching dates were doublepeaked in at least three or four (if more flexible criteria for double-peaking are adopted) of eight apparently prolonged breeding seasons (Fig. 1). Almost all other records of egg-laying and hatching dates for Curlew Sandpipers at Taimyr and Yamal, from literature sources, fell within the broad range of breeding dates (Fig. 1). However, the earliest hatching dates in the majority of Taimyr sites/seasons, fell between 5 and 12 July (recorded in 14 of 21 sites/seasons), with three earlier and four later dates of beginning of hatching. This main period of the start of hatching corresponds to the first complete clutches on 15­22 June. The earliest breeding on Taimyr was recorded in the Knipovich Bay area (Fig. 1) where a brood of chicks of two days old was found on 2 July 1991, suggesting a start of egglaying on at least 8 June. The latest breeding on Taimyr was recorded for Cape Sterlegov with hatching on 4 August 1994 (Tulp et al. 1998). Other late breeding events are known from the lower Lenivaya River area in 1983 (Tomkovich & Vronski 1988), and other early breeding events were recorded in the Medusa Bay area in 2000 and 2001 (Tulp et al. 2000, Tulp & Schekkerman 2001). There are only anecdotal observations of Curlew Sandpipers breeding in Yakutia and Chukotka. However, it is striking that most records of nests and chicks (13 studies) indicated early laying or hatching dates within a brief period (start of incubation on 14­21 June, hatching on 4­10 July). In one study (Stishov & Maryukhnich 1990), two complete clutches were found even earlier, on 5 June (calculated hatching date of 25 June). These data indicate earlier breeding in East Siberia as compared to Taimyr. Departure Departure of Curlew Sandpipers from breeding grounds is less conspicuous than arrival, and therefore many contradictory statements exist. Contrary to some early studies (e.g. Birula in Pleske 1928, Gladkov 1951, Sdobnikov 1959) it is clear now that southward migration starts earlier than in late July or August. Appearance of non-displaying males in groups or in flocks with other waders was reported to start 30 June onwards in northern Taimyr (Tomkovich & Vronski 1988, HÆtker 1995). Their pronounced migration was seen in coastal areas in early July (Tomkovich & Vronski 1994, Tomkovich et al. 1994, HÆtker 1995, Khomenko et al. 1999, Felix & van Tornhout in litt.). Tulp & Schekkerman (2001) considered that "a peak consisting of males leaving the tundra was visible late June­ early July" in 2001. Observations of last territorial males in northern Taimyr were made between 2 and 11 July in eight seasons or sites (six studies). The latest adult males on Taimyr were recorded between 12 and 14 July (Tomkovich et al. 1994, collection of Zool. Inst. in St. Petersburg). The period of adult female migration varies greatly in relation to breeding success in a season, and possibly to time


Tomkovich & Soloviev: Schedule and geographic distribution on the breeding grounds

23

of breeding. Some females that fail to breed may start their post-breeding migration together with males, although this has not been documented. Unsuccessful females were collected from flocks in the second 10-day period of July, and they formed a migration peak in northern Taimyr in this period in seasons with heavy nest predation (Tomkovich et al. 1994). In such unsuccessful seasons, the very last Curlew Sandpipers could be observed in mid-July (Taimyr in 1992: Spieckman & Groen 1993, in 1997: Khomenko et al. 1999), or even on 6 July (Alaska in 1962: Holmes & Pitelka 1964). The peak of adult female migration in years of good breeding success was delayed till the end of July (Tomkovich et al. 1994, Schekkerman et al . 1998, Tulp and Schekkerman 2001). The latest females giving alarm near their young on Taimyr were recorded on 5­11 August in four seasons, and in two cases these were last records of females in a season. Nevertheless, several other records of adult birds between 12 and 15 August are known for Taimyr. An interesting observation related to Curlew Sandpiper departure was made by Sdobnikov (1959), who stated that most post-breeding flocks were found on the coastal tundra of Taimyr, not inland. Information obtained in recent decades does not contradict this suggestion. Young Curlew Sandpipers can be totally absent in seasons with high predation, as in 1992 (Spiekman & Groen 1993, Tomkovich et al. 1994). In other seasons, independent, fullgrown young occur in groups on Taimyr, starting from 27 July to 8 August onward in different years. Active passage of young birds was recorded during the first 10-day period of August in several studies. The latest records for Taimyr were on 1­10 September (Pleske 1928, Kozlova 1962, Tomkovich & Vronski 1988). Little information on departure and migration of Curlew Sandpipers exists for areas east of Taimyr. All records of migrating adults were from July, apart from one strange observation of a group consisting of young birds and one adult on the New Siberian Islands on 28 August (Rutilevski 1963). Uspenski (1965) described active migration of young birds with few adults in the Anabar River area in late July (earlier than on Taimyr). Apart from the above-mentioned strange record, other latest observations of the species belong to the second 10-day period of August (Kondratyev 1982, Stishov et al. 1991, Akhmadeeva et al. 1994), which is also earlier than on Taimyr. AN UTTER PANMIXY VERSUS GEOGRAPHIC POPULATIONS The absence of morphological differentiation between Curlew Sandpipers from different parts of the species' range (e.g. Portenko 1972, Melville 1981, Wymenga et al. 1990, Underhill 1995, Engelmoer & Roselaar 1998), the outlined opportunistic behaviour (pair formation on migration and on male breeding territories, negligible breeding-site fidelity, density fluctuations between and within a season at a site), as well as communal breeding of birds belonging to different flyways, all indicate panmixy of breeding birds within the species' breeding range. Based on such indirect evidence, the idea of panmixy was expressed in some studies (Tomkovich & Soloviev 1994, Underhill 1995, Lappo 1996). Nevertheless, we consider here that panmixing is not complete within the species' population. Two lines of evidence exist in support of this. Firstly, the above overview of the Curlew Sandpiper's migration and breeding schedule shows that all these events start, and possibly terminate, earlier in the eastern parts of the
Fig. 1. Distribution of dates of clutch completion in the Curlew Sandpiper. Number of clutches initiated on a given day is on the vertical axis; abbreviations correspond to the following sites and sources: KB ­ Knipovich Bay (Tomkovich & Soloviev 1994), PL ­ Pronchischev Lake, (Schekkerman & van Romen 1995, Spiekman & Groen 1993), PD ­ Pyasina River Delta (Stock & Bruns 1995), MB ­ Medusa Bay (Tulp et al. 1997, 2000).

species' breeding range. It seems that this difference is consistent, as can be seen from arrival dates. Secondly, according to recovery data, most birds from the Taimyr breeding population migrate towards African nonbreeding grounds (Tomkovich et al. 2000), and Curlew Sandpipers ringed in Africa have been recovered at the Yana River (c.135°E) at the furthest east (Elliott et al. 1976, Gromadzka 1985, Underhill 1995, Underhill et al. 1999, Pozdnyakov 2006). At the same time, a strong connection of Australian non-breeding quarters to East Siberian breeding grounds is evidenced by the results of ringing and colour-marking (Minton 1998). Central Taimyr (98°30'E) is the westernmost


24

International Wader Studies 19

Fig. 2. Covariation of breeding dates (clutch completion dates) and densities of Curlew Sandpipers at different sites in northern Taimyr in `normal' (open rectangles) and `late' (filled rectangles) seasons. Rectangle width increases with nesting density.

area where an Australian Curlew Sandpiper has been recorded (Tomkovich et al. 1994, Minton 1998). These recovery data are supported by direct observations of migrating Curlew Sandpipers. In several studies in northern Taimyr, a majority of Curlew Sandpipers migrated to the east and north-east in the pre-breeding period, and in the opposite direction in the post-breeding period (Sdobnikov 1959, Tomkovich & Vronsky 1988a,b, 1994, Tomkovich et al. 1994, Frodin et al. 1994a, HÆtker 1995, Schekkerman et al. 1998). In south-eastern Taimyr (72°51'N, 106°02'E), 48% of Curlew Sandpipers migrated to the west and north-west in the pre-breeding period, while 23% of birds moved to the east and north-east (MYS unpubl. data). Northward passage further east, near the Indigirka Delta, was directed northwestward (Uspenski et al. 1962). Thus, in spite of the broad overlap in breeding distribution of Curlew Sandpipers originating from African and Australian non-breeding grounds, clear differences exist between birds which inhabit western to central Taimyr, and more eastern breeding areas. They have generally different directions of migrations and slightly different migration and breeding schedules. Hence we are inclined to consider within the Curlew Sandpiper's breeding range two geographic breeding populations which overlap to a relatively small extent. Females from eastern and western parts of the breeding range also have some differences in plumage (Cramp & Simmons 1983). In addition, a tendency towards differentiation was observed in the mtDNA from samples obtained from flyways to western Africa and Australia (Wennerberg 2001). A MODEL FOR TIMING OF BREEDING EVENTS AND DISTRIBUTION OF THE TAIMYR CURLEW SANDPIPERS Available data clearly indicate annual and possibly intra-year redistribution of breeding Curlew Sandpipers, at least within the Taimyr population's breeding range. In addition, variation in breeding dates, as well as cases of double-peak breeding, are common in the population. All these characteristics at least partly relate to snow and weather conditions on arrival in June. To illustrate this relationship, we propose a model that considers normal and late-spring conditions separately (Fig. 2). Curlew Sandpiper males need snow patches for their territorial activity. Snow cover almost always disappears first and quicker in southern and central areas of the species' breeding range, thus creating the possibility that birds in the northernmost areas breed later. However, at the beginning of arrival, many migrating Curlew Sandpiper pairs do not stop

at the first suitable area they encounter, but often reach remote parts of their breeding range and may start breeding there if conditions allow. This explains why the onset of breeding does not differ much between southern and northern areas, except when conditions are extreme (such as in 1992) when breeding at the beginning of the season in northernmost areas is prevented by complete snow cover. This also explains why, in early or normal spring events, local egglaying periods are shorter in southern and central parts of the species' breeding range than in northern parts: quicker snowmelt in the south does not permit late breeding there. The possibility of longer breeding and peculiar intra-population movements are probably responsible for the Curlew Sandpiper having the least synchronised breeding among waders in northern Taimyr (Schekkerman & van Roomen 1995, Soloviev & Tomkovich 1997). Changes in snow conditions also provide a plausible explanation for a variation in breeding density of Curlew Sandpipers. Quick snowmelt in southern areas in early or normal seasons leads to a lower breeding density there, because only the early fraction of potential breeders settle down, while others move elsewhere. In cold seasons, some pairs may breed further south than normally and more birds settle down in southern parts of the core area (Fig. 2). In the absence of snow, Curlew Sandpipers not only settle down in lower densities, but males also disappear earlier from southern parts of the breeding range. This pattern may be substantially modified in seasons of high nest predation: both disappearance of pairs after egg loss and re-nesting females found among late breeders in northernmost Taimyr indicate possible mass movement of failed breeders to the north to make a second nesting attempt. Heavy snowfalls during the egg-laying/early incubation period, as in 1997 in the Medusa Bay area (Khomenko et al. 1999), may also strongly influence distribution and numbers of Curlew Sandpipers, resulting in a majority of pairs making re-nesting attempts. DOUBLE-PEAK BREEDING The bimodal distribution of breeding dates in the Curlew Sandpiper was found in some seasons in northern Taimyr (Fig. 1) and is reflected in the suggested population model (Fig. 2). At least four explanations for the phenomenon can be considered. 1. A flyway population hypothesis A difference in time of arrival and start of breeding of several days between populations was shown above, with later


Tomkovich & Soloviev: Schedule and geographic distribution on the breeding grounds

25

events at Taimyr and earlier further east. It can be speculated that the early wave of breeding is by birds of the `eastern' population. Appearance of these `eastern' birds may indeed explain `outliers' at arrival (see Table 1) and unusually early breeding in the Knipovich Bay area in 1991 (Fig. 1). Nevertheless, it seems unlikely that the whole `wave' of early breeders belongs to the `eastern' population. There are no indications that pre-breeding migration of Curlew Sandpipers in northern Taimyr changes direction from an initial easterly or south-easterly course to westerly later. The migration direction can change in successive days (Tomkovich & Vronski 1988, Tomkovich et al. 1994), but it generally heads to the north-east and east. In any event, there is no large time difference between migration influxes to explain the gap of at least four days between the two nesting `waves'. Moreover, if two peaks of breeding resulted from different geographic populations, these peaks could be expected to be evident through the whole breeding range in Taimyr, not only in its northern parts. 2. Breeding interruption by inclement weather Assuming that pairs need 4­5 days at a site before starting to lay eggs (unpubl. data; n = 4), a comparison of laying dates (Fig. 1) with weather data for sites/years when a bimodal distribution of breeding dates was recorded (Underhill et al. 1993, Tomkovich et al. 1994, Stock & Bruns 1995, Schekkerman & van Roomen 1995), fails to reveal a relationship between weather and dates of pairs settling down. Even the opposite was recorded in the Pyasina Delta in 1990 (16­ 23 June), when calculated dates for settling down of pairs of the second breeding "wave" overlapped broadly with a period of unfavourable weather (13­21 June; Stock & Bruns 1995). 3. Successive breeding of first and second females with polygynous males Although a gap of several days was observed between successive matings of a territorial male with different females, only a few cases of successive polygeny were documented during our five-year study in northern Taimyr. Most males mated only once in a season, and some of them not even once. Moreover, many males arrive in the northern breeding areas too late to undertake two matings. Therefore, the large second wave of nesting in northern Taimyr cannot be exclusively explained by successive polygyny, although some contribution is possible. 4. Northward drift for re-nesting This explanation agrees well with available data both on a northward drift of birds during June, and on late re-nesting attempts. Nevertheless, the data are fragmentary and further support for the hypothesis is necessary. Well-defined peaks can be due to higher egg survival during the first week of a nesting season, before recognition of the new food resource by predators (e.g. JÆnsson 1991, Tomkovich 1995a). This would result in a gap between a mass start of Curlew Sandpiper nesting in mid-June and re-nesting attempts, generally farther north, in late June and early July. CONCLUSIONS An interaction of inter- and intra-seasonal redistribution of birds with a polygynous breeding system and re-nesting, is responsible for a peculiar breeding population structure and

breeding schedule in the Curlew Sandpiper. The following succession of events is the most realistic model of the situation in `normal' years. The first pairs of Curlew Sandpipers to arrive, distribute through the breeding range according to available snow-free habitats, and a majority settle down in southern parts of the breeding range. Sociality of new arrivals makes them settle close to early pairs, and thus increase the concentration of birds in southern areas. After egg-laying, as snowmelt and predation on clutches develop, most males and females with failed nests move further north in Taimyr for a new breeding attempt. Here snow disappears later and the environment corresponds to an earlier stage of spring in the south. Nesting of these birds form the second wave of breeding. It is impossible to discount that some females may breed in this second wave for the first time in the season. Restriction of male southward departure to early July, creates the most obvious limit for re-nesting attempts (Fig. 2). In late or cold seasons, birds can find suitable conditions in the south. This permits them to nest and re-nest at lower latitudes, a reason for a different pattern of intra-seasonal redistribution for breeding. ACKNOWLEDGEMENTS Much of the data were collected in 1990­92 in the Knipovich Bay area, in one of the field camps of the International Arctic Expedition, Institute of Ecology and Evolution, Russian Academy of Sciences, under the leadership of Prof. E.E. Syroechkovski. We are thankful to R. Felix, S.V. Khomenko, J. Pearce, V.K. Ryabitsev, and C. van Turnhout for putting their unpublished data at our disposal. REFERENCES
Akhmadeeva, I.A., Karpov, N.S.,Klimovski, I.V., Kuz'min, O.V., Milulenko, K.I., Pozdnyakov, V.I. Safronov, V.M. & Skryabin R.M. 1994. State of nature complexes of Kotel'ny Island (New Siberian Archipelago): Materials of the Arctic Expedition, 1993. Yakutsk: Yakutian Sci. Center of Russian Acad. Sci. (in Russian). Cramp, S. & Simmons, K.E.L. (Eds) 1983. Birds of the Western Palearctic. Vol. 3. Oxford: Oxford University Press. Elliott, C.C.H., Waltner, M., Underhill, L.G., Pringle, J.S. & Dick, W.J.A. 1976. The migration system of the Curlew Sandpiper Calidris ferruginea in Africa. Ostrich 47: 191­213. Engelmoer, M. & Roselaar, C.S. 1998. Geographical Variation in Waders. Dordrecht: Kluwer Frodin, P., Haas, F. & LindstrÆm, A. 1994a. Bird migration at Sibiryakov Island, Taimyr, Siberia in early summer 1992. Lund: Report: Dept. of Ecol., Lund Univ. Frodin, P., Haas, F. & LindstrÆm, A. 1994b. Mate guarding by Curlew Sandpiper ( Calidris ferruginea ) during spring migration in North Siberia. Arctic 47: 142­144. Gladkov, N.A. 1951. Order Limicolae. In: Dementyev, G.P. & Gladkov, N.A. (Eds). Birds of the Soviet Union. Vol. 3. Moscow, Sovetskaya Nauka: 3­372. (in Russian) Gromadzka, J. 1985. Curlew Sandpiper ­ Calidris ferruginea (Pontopp.). In: Viksne, A.Ya. & Mikhelson, Kh. A. (eds.). Migrations of birds of Eastern Europe and Northern Asia: Gruiformes ­ Charadriiformes: 185­193. Moscow: Nauka. (in Russian) Haviland, M.D. 1915. Notes on the breeding habits of the Curlew Sandpiper. Brit. Birds 8: 178­183. Hertzler, I. & GÝnter, K. 1994. International Arctic Expedition 1994 ­ Medusa Bay. Unpubl. report. Holmes, R.T. & Pitelka, F.A. 1964. Breeding behavior and taxonomic relationships of the Curlew Sandpiper. Auk 81: 362­379. HÆtker, H. 1995. Avifaunistical records of the WWF Expedition to Taimyr in the years 1989, 1990 and 1991. In: Prokosch, P. & HÆtker, H. (Eds) Faunistik und Naturschutz auf Taimur ­ Expeditionen 1989­1991. Sonderheft der Schriftenreihe Nationalpark Schleswig-Holsteinisches Wattenmeer. Corax 16 Sonderheft: 34­89.


26

International Wader Studies 19 lew Sandpiper at Yakan Cape (the arctic coast of Chukotka). In: Yurlov, A.K. (Ed.) Information of the Working Group on Waders. Novosibirsk: Biol. Inst. of Russian Acad. Sci.: 66. (in Russian) Stock, M. & Bruns, H.A. 1995. Wetter, Schnee und Eislage. In: Prokosch, P. & H Æ tker, H. (Eds) Faunistik und Naturschutz auf Taimur­ Expeditionen 1989­1991. Sonderheft der Schriftenreihe Nationalpark Schleswig-Holsteinisches Wattenmeer Corax 16, Sonderheft: 17­24. Tomkovich, P.S. 1988a. Mating system and parental care in Curlew Sandpiper at the Taimyr. In: Andreev, A.V. & Kondratyev, A.Ya. (Eds.). Studies and Protection of Birds in Northern Ecosystems. Vladivostok: Far-Eastern Branch, USSR Acad. of Sci.: 180­184. (in Russian) Tomkovich, P.S. 1988b. The birds of the southern coast of the BuorKhaya Gulf, Northern Yakutia. Archives of Zool. Mus., Moscow State Univ. 26: 3­38. (in Russian) Tomkovich, P.S. 1995a. Breeding biology and breeding success of the Spoon-billed Sandpiper Eurynorhynchus pygmeus. Russ. J. Ornithol. 4: 77­91. (in Russian) Tomkovich, P.S. 1995b. Does the wind influence egg fertility? A probable case with Curlew Sandpiper. Wader Study Group Bull. 77: 48­49. Tomkovich, P.S. & Soloviev, M.Yu. 1994. Site fidelity in High Arctic breeding waders. Ostrich 65: 174­180. Tomkovich, P.S. & Vronski, N.V. 1988a. Avifauna and bird populations of the arctic tundras on the Khariton Laptev Coast (northwestern Taimyr). In: Rogacheva, H.V. (Ed.) Contributions to the fauna of Central Siberia and adjacent regions of Mongolia. Moscow: Inst. of Animal Morph. and Ecol., USSR: 5­47. (in Russian) Tomkovich, P.S. & Vronski, N.V. 1988b. Bird fauna of the Dickson area. Archives of Zool. Mus., Moscow State Univ. 26: 39­77 (in Russian) Tomkovich, P.S. & Vronski, N.V. 1994. Birds of lower reaches of the Uboynaya River (North-Western Taimyr). In: Rogacheva, E.V. (Ed.) Arctic Tundras of Taimyr and Kara Sea Islands: Nature, Fauna and Conservation Problems. Vol 1. Moscow: Inst. Ecol. and Evol., Russian Acad. Sci.: 161­206. (in Russian) Tomkovich, P.S., Soloviev, M.Yu. & Syroechkovski, E.E., Jr. 1994. Birds of arctic tundras of northern Taimyr, Knipovich Bay area. In: Rogacheva, H.V. (Ed.) Arctic Tundras of Taimyr and Kara Sea Islands: Nature, Fauna Conservation Problems. Vol 1. Moscow: Inst. of Animal Morph. and Ecol., USSR Acad. Sci.: 41­107. (in Russian) Tomkovich, P.S., Lappo, E.G. & Syroechkovski, E.E., Jr. 2000. Ringing and migratory links of Taimyr waders. In: Ebbinge, B.S., Mazourov, Yu.L. & Tomkovich, P.S. (Eds) Heritage of the Russian Arctic: Research, Conservation and International Co-operation: 458­ 475. Moscow, Ecopros Publishers. Tulp, I., Bruinzeel, L., Jukema, J. & Stepanova, O. 1997. Breeding Waders at Medusa Bay, Western Taimyr, in 1996. WIWO Report 57. Zeist: WIWO. Tulp, I., Schekkerman, H., Piersma, T., Jukema, J., de Goeij, P. & van de Kam, J. 1998. Breeding Waders at Cape Sterlegova, Northern Taimyr, in 1994. WIWO report 61. Zeist: WIWO. Tulp, I., Schekkerman, H. & Klaassen. R. 2000. Studies on breeding shorebirds at Medusa Bay, Taimyr, in summer 2000. Wageningen: Alterra Green World Research. Alterra Report 219. Tulp, I. & Schekkerman, H. 2001. Studies on breeding shorebirds at Medusa Bay, Taimyr, in summer 2001. Wageningen: Alterra Green World Research. Alterra Report 451. Underhill, L.G. 1995. The relationship between breeding and nonbreeding localities of waders: the Curlew Sandpiper Calidris ferruginea as an example. Ostrich 66: 41­46. Underhill, L.G., Pry s-Jones, R.P., Syroechkovski, E.E., jr., Groen, ^ N.M., Karpov, V., Lappo, H.G., van Roomen, M.W.J., Rybkin, A., Schekkerman, H., Spiekman, H. & Summers, R.W. 1993. Breeding of waders (Charadrii) and Brent Geese Branta bernicla bernicla at Pronchishcheva Lake, northeastern Taimyr, Russia, in a peak and a decreasing lemming year. Ibis 135: 277­292. Underhill, L.G., Tree, A.J., Oschadleus, H.D. & Parker, V. 1999. Review of Ring Recoveries of Waterbirds in Southern Africa. Cape Town: Avian Demography Unit, Univ. of Cape Town. Uspenski, S.M. 1965. Materials on the bird fauna of Anabar tundra. Archives of Zool. Mus., Moscow State Univ. 9: 63­97. (in Russian) Uspenski, S.M. Boehme, R.L., Priklonski, S.G. & Vekhov, V.N. 1962. The birds of north-eastern Yakutia. Ornithologia 4: 64­86. (in Russian) Wennerberg, L. 2001. Genetic variation and migration of waders. PhD thesis. Lund University, Sweden. Wymenga, E., Engelmoer, M., Smit, C.J. & van Spanje, T.M. 1990. Geographical breeding origin and migration of waders wintering in West Africa. Ardea 78: 83­112.

JÆnsson, P.E. 1991. Reproduction and survival in a declining population of the Southern Dunlin Calidris alpina schinzii. Wader Study Group Bull. 61 Suppl.: 56­68. Kharitoniv, S.P. 2002. An overview of the main studies of waders and other birds at the Willem Barents Station, north-western Taimyr. In: Tomkovich, P.S. & Shubin, A.O. (Eds). Information Materials of the Working Group on Waders. Moscow: 25­28. Khomenko, S., Rosenfeld, S. & Dylyuk, S. 1999. Birds of Medusa Bay, NW Taimyr, in 1997. WIWO Report 66. Zeist: WIWO. Kondratyev, A.Ya. 1982. Biology of Waders in Tundras of North-Eastern Asia. Moscow: Nauka. (in Russian). Kozlova, E.V. 1962. Charadriiformes. Suborder Limicolae. In: Fauna of the USSR. Birds. Vol.2, issue 1, part 3. Moscow & Leningrad: Acad. Sci. USSR. (in Russian) Kretchmar, A.V. & Leonovich, V.V. 1965. Spring migration of birds on Western Taimyr. Ornithologia 7: 29­35 (in Russian). Lappo, E.G. 1996. Comparison of breeding range structure for Dunlin Calidris alpina and Curlew Sandpiper Calidris ferruginea: conservative and nomadic tundra waders. Wader Study Group Bull. 80: 41­46. Lappo, E.G. & Tomkovich, P.S. 2006. Limits and structure of the breeding range of the Curlew Sandpiper Calidris ferruginea. Int. Wader Studies 19: 9­18. Leonovich, V.V. & Veprintsev, B.N. 1980. Biology of the Curlew Sandpiper (Calidris ferruginea). In: Flint, V.E. (Ed.) News in Studies of Biology and Distribution of Waders. Moscow: Nauka: 153­155. (in Russian) Melville, D.S. 1981. Spring measurements, weight and plumage status of Calidris ruficollis and Calidris ferruginea in Hong Kong. Wader Study Group Bull. 33: 18­21. Minton, C. 1996. Overseas movements of Red-necked Stints and Curlew Sandpipers. Victorian Wader Study Group Bull. 20: 39­43. Minton, C. 1998. Migratory movements of Curlew Sandpiper Calidris ferruginea that spend the non-breeding season in Australia. Stilt 32: 28­40. Pearce, J.M., Esler, D. & Degtyarev, A.G. 1998. Birds of the Indigirka River delta, Russia: historical and biogeographic comparisons. Arctic 51: 361­370. Pitelka, F.A., Holmes, R.T., MacLean, S.F., Jr. 1974. Ecology and evolution of social organization in arctic sandpipers. Amer. Zool. 14: 185­ 204. Pleske, T. 1928. Birds of the Eurasian tundra. Mem. Boston Soc. Nat. Hist. 6: 107­485. Portenko, L.A. 1959. Studien an einegen seltenen Limicolen aus dem nordlichen und ostlichen Siberien II. Der Sichelstrandlaufer. J. Ornithol. 100: 141­172. Portenko, L.A. 1972. The Birds of Chukchi Peninsula and Wrangel Island. Part 1. Leningrad: Nauka. (in Russian) Priklonski, S.G., Boehme, R.L. & Uspenski, S.M. 1962. Materials on bird migration in the Indigirka River delta. In: Pokrovski, V.S. (Ed.) Migrations of Animals. Vol. 3145­159. Moscow: USSR Acad. Sci.: 153­155. (in Russian) Rutilevski, G.P. 1958. Birds of Bolshoi Lyakhovski Island. Problemy Arctiki 4: 79­90. (in Russian) Rutilevski, G.P. 1963. Birds of Stilbovoi Island. Transactions of Arctic and Antarctic Res. Inst. 224: 93­117. (in Russian) Ryabitsev, V.K. & Alekseeva, N.S. 1998. Nesting density, dynamics and site tenacity of waders on the middle and northern Yamal. Int. Waders Studies 10: 195­200. Schekkerman, H. & van Roomen, M. 1995. Breeding Waders at Pronchishcheva Lake, Northeastern Taimyr, Siberia, in 1991. WIWO Report 55. Zeist: WIWO. Schekkerman, H., van Roomen, M.W.J. & Underhill, L.G. 1998. Growth, behaviour of broods and weather-related variation in breeding productivity of Curlew Sandpipers Calidris ferruginea. Ardea 86: 153­168. Sdobnikov, V.M. 1959. Waders of northern Taimyr. Transactions of Agriculture Inst. for the Extreme North 9: 184­207 (in Russian) Soloviev, M.Y., Golovnyuk, V.V., Rakhimberdiev, E.N. & Travina, I.V. 2003. Breeding conditions and numbers of birds on south eastern Taimyr, 2002. Unpubl. report. Spiekman, H. & Groen, N. 1993. Breeding Performance of Arctic Waders in Relation to Lemming Densities, North-east Taimyr, Siberia, 1992. WIWO Report 33. Zeist: WIWO. Stishov, M.S., Prodatko, V.I. & Baranyuk, V.V. 1991. Birds of Wrangel Island. Novosibirsk: Nauka. (in Russian) Stishov, M.S. & Maryukhnich, P.V. 1992. Nesting of Red Knot and Cur-