Body mass changes in waders (Charadrii) in a high arctic area at northern Taimyr, Siberia

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<ul><li><p>271 </p><p>Body Mass Changes in Waders (Charadrii) in a High Arctic Area at Northern Taimyr, Siberia </p><p>Mikhail Y. Soloviev and Pavel $. Tomkovich </p><p>SOLOWEV, M. Y. &amp; R S. ToivnvowcH (1997): Body mass changes in waders (Charadrii) in a high arctic area at northern Taimyr, Siberia. J. Orn. 139: 271-281. - Body mass data were collected for 5 species of tundra waders during 6 breeding seasons to study variation in nutrient reserves relative to high arctic climatic conditions and the stage of reproduction. Structural size was accounted for by the 1st Principal Component of external linear measure- ments: wing length, bill length and tarsus length. Sandpipers Calidris spp. were on average lighter in phenologically late seasons, while mass of Turnstones (Arenaria interpres) was similar in all years. Mass of waders was lower during brood-rearing than during incubation. Body mass during pre-nesting was most variable between years, reflecting the unpredictable weather conditions in this period. Monogamous species (Knots Calidris canl~tUs and Turnstones) began to breed earlier, and were on average, as hea W during the pre-nesting period as during incubation. In contrast, species with a proven or suspected rapid double- clutch breeding system (Little Stints C. rninuta and Sanderlings C. alba) began to breed later and had during the laying period masses close to those of adults attending broods, and lower than during incubation. Body mass of the two latter species and Curlew Sandpipers (Calidris ferruginea) varied during incubation, reaching peak at 7 to 13 days after clutch completion. </p><p>(MYS) Department of Vertebrate Zoology and General Ecology, Biological Faculty, Moscow State University, 119899 Moscow, Russia; (PST) Zoological Museum of Moscow State University; Bol. Nikitskaya Str. 6, 103009 Moscow, Russia. </p><p>Introduction </p><p>Waders (Charadrii) go through significant changes in body mass in the course of the annual cycle Variation in mass has been most thoroughly studied ha wintering areas and on migration routes. These studies have been instrumental in understanding wader adaptations to long-distant flights and survival in winter (e,g. Jonson 1985, SUMMERS et al. 1987, ENS et al. 1990, CASTRO et al. 1992, Su~t~vmRs et al. 1992, LIND- STROM &amp; PmRSMA 1993). During reproduction, waders engage in a number of energy demanding activities like territory defense, egg-laying, incubation rand attending young that should be reflected in changes of body mass. Energetics of r~producfion must be especially limiting in the harsh climatic conditions of the Arctic, which is used for breeding by many wader species. However, previously studies of wader mass dynamics at their breeding grounds in the High Arctic were focused mainly on certain periods within a breeding season (~ g., MORRISON &amp; DAVIDSON 1990, PIERSMA &amp; MORVdSON 1994), and usually did not provide material for inter-year comparison. The most recent studies at the Taimyr peninsula revealed a peak of body mass during incubation compared to brood-rearing in Sandertings (Calidris alba; SoLovmv &amp; TOMKOVICH </p></li><li><p>272 Journal fiir Ornithologie 138, 1997 </p><p>1995), Little Stints (Calidris rninuta) and Curlew Sandpipers (Calidris ferruginea; SCHEKKERMA?q &amp; VAN ROOMEN 1995). However, for wader species other than the Sanderling, neither patterns of body mass dynamics in the pre-nesting period, nor the influence of a season's phenology on body mass changes are known. Since three previously considered species belong to uniparental incubators, no data is available on regularities of mass changes in waders with both parents participating in incubation. Addressing these problems, we undertake comparative analysis of patterns of mass dynamics in Little Stints, Curlew Sandpipers, Knots (Calidris canutus) and Turnstones (Arenaria interpres) inhabiting different localities of northern and northwestern Taimyr, Siberia, in an attempt to understand adaptations to the environment of the High Arctic. When studying variation of body mass within breeding stages we also re-analyzed the Sanderling data, because this problem was not accounted for in our previous study of this species. </p><p>Materials and methods </p><p>Data were collected within the arctic tundra subzone of the Taimyr peninsula (CHn</p></li><li><p>M. Y. SoLovmv &amp; R S. TOMKOVICH: Mass changes in waders 273 </p><p>behavior of marked birds, breadth of cloaca, measured with a ruler to the nearest 0.5 ram. As waders are sexually dimorphic with respect to size, discriminant analysis of linear measure- ments increased the sample sizes of Sanderlings and Little Stints, sexed with probability exceeding 0.9. All the sexing procedures are described in detail in SoLovmv &amp; TOMKOVlCH (t995). </p><p>Analysis of variance (ANOVA; AFIn &amp; AZ~N 1979) was used for statistical analysis of body mass. To control for the effect of nutrient-reserve independent structural size (PmRsMa 1984) on mass, we included the first principal component of wing length, bill length and tarsus length (PC1) in the model as a covariate, which transformed ANOVA into analysis of covariance (ANACOVA). </p><p>The basic ANACOVA included three factors with fixed effects: (1) sex (male and female); (2) breeding state (birds in the pre-nesting period, incubating birds, and birds attending broods); (3) year ('normal' and 'late'). Pairwise interactions of factors were included in the model. If the influence of the main effect of sex and its interactions was found insignificant we excluded it from further reestimates, which permitted us to enlarge the sample size by using unsexed birds. Since male Curlew Sandpipers do not participate in incubation and attending broods (ToMKOVlCH 1988), and leave breeding grounds in early July, regardless of the current stage of incubation by females, estimates were made separately for females and pre-nesting males, for this species. To check whether the date rather than the breeding state was responsible for body mass change during the season, we constructed models without the factor 'breeding state', but instead including the Julian date as the covariate (in the form of a linear or quadratic function). </p><p>Dates of clutch completion were determined for 432 nests of five species in order to check whether temporal differences between species in reproductive strategies are connected some- how with the pattern of mass dynamics during breeding season, and to study variation of mass within breeding states. These dates were derived from direct observations of laying birds, or back-calculated from the hatching dates on the basis of incubation periods determined by TOMKOVICH et al. (1994). Since data on the dates of clutch completion were not available for pre-nesting birds and also entirely missing or extremely scarce in different species of waders in the late years 1983 and 1992, we estimated separate ANACOVA (when the factor 'sex' parti- cipated) or multiple regression models with PC1 of linear measurements and the time after clutch completion in the form of linear and quadratic functions as independent variables separ- ately for periods of incubation and brood-rearing in normal seasons. </p><p>Analysis of studentized residuals allowed us to detect one to two outliers in every species' sample which were excluded from further calculations. Statistical e~imates and graphs were made using SYSTAT 5.0 (WiLKiNSON 1990). </p><p>The studies of PST in 1982--84 were financed by the Zoological Museum of the Moscow State University, while the data of 1990-92 were collected by both the authors in the field camp of the International Arctic Expedition of the Institute of Ecology and Evolution, Russian Academy of Sciences, thanks to the financial and logistic support of the expedition organizers. Therefore we express our gratitude to the head of the expedition, Acad. E. E. SYROEC~KOVSX~, and to the expedition staff, especially to N. V. VRONSKY, E. E. SYROECHKOVSKI Jr., M. M. ZAB~LIN, M. G. SINITSYN, A. ABo~Ivs. The study- of MYS was also supported by grant ~ 96-04-49290 of the Russian Fund for Fundamental Studies awarded to G. N. S~KiN. We greatly appreciated the pleasant company and the help in the search for nests and bird catching of the expedition participants in different years: O. HaLngN, E. G. Lappo, G. Th. n~ Roos, A. V. R~xIN, E. E. SYROeCHKOVSSI Jr., N. V. VRONSKY, V. O. YAKOVLeV, R Y~sou. We are thankful to I. BVRKJ~DaL, H. HOT~:ZR, J. S. SEDINOER and tk SUMMERS for valuable comments on the manuscript, and to J. TUR~BULL for correcting the English in the final draft. </p></li><li><p>274 Journal fiir Ornithologie 138, 1997 </p><p>Results </p><p>The data on body mass of waders in different seasons and breeding states are sum- marized in Table 1. Inclusion of the date in statistical models instead of the factor of breeding state resulted in a decrease of multiple square correlation coefficients, in- dicating a reduction of models' fitness, and the Julian date was not considered in the further re-estimates. The measure of structural size, the first principal component of wing, bill and tarsus length was responsible for 47 to 66 % of their total variance in different species. In the ANACOVA PC1 score was significantly related to body mass of Curlew Sandpipers (P0.9). Body mass of Sanderlings and Little Stints was influenced by sex (P0.25). Interaction of sex with other factors was not significant for all species (P&gt;0.25). On this basis, both the main effect of sex and its interactions were excluded from further re-estimates for Knots and Turnstones, while models for Sanderlings and Little Stints retained the main effect of sex. </p><p>The breeding state had a significant effect on body mass in sandpipers (P</p></li><li><p>M. Y. SOLOVIEV &amp; I). S. TOMKOVICH: Mass changes in waders 275 </p><p>brood-rearing waders, was the most pronounced change in mass and was common to all species (Table 2; P0.4), the former species significantly differing (P</p></li><li><p>276 Journal f/ir Ornithologie 138, 1997 </p><p>between-year difference in median dates was smaller (5.5 to 6.5 days), but more signifi- cant (P0.136, for pairwise MW; Figure). These species were followed by Little Stints, having significantly later median dates (P0.15). This particular feature of Curlew Sandpipers is explained by the bimodal type of their arrival to the breeding grounds, when a portion of birds are the first to appear already in pairs, while an additional party of females arrives later and consequently begins to breed later (Toiv~ovIcu et al. 1994). </p><p>July 20 </p><p>10 </p><p>June 30 * </p><p>10 t n=15 </p><p>Turnstone </p><p>n=52 n=68 n=133 n=60 </p><p>Knot Curlew Little Sanderling Sandpiper Stint </p><p>The dates of clutch completion in five wader species in 'normal' years at Northern Taimyr. Box plots show nonparametric statistics: median, quartiles, and outside values of the data (asterisks). </p></li><li><p>M. Y. SoLoxaEv &amp; P. S. TOMKOVICH: Mass changes in waders 277 </p><p>The date relative to time of clutch completion contributed significantly both as linear and quadratic functions to variation of mass during incubation in 'normal' seasons in Little Stints (P</p></li><li><p>278 Journal fiir Ornithologie 138, 1997 </p><p>periods of negative energy budget (DUGAN et al. 1981). The field metabolic rate of Knots during the temperate winter period is about 4 times the basal metabolic rate at this time of the year (POOT &amp; PIERSMA 1994), being identical with measured field metabolic rates of a similarly sized shorebird species, the Turnstone during the incuba- tion period in the Canadian High Arctic (PIEr, SMA &amp; MORRISON 1994). </p><p>A possible advantage of lower mass during brood-rearing as adaptation to cheaper flight when performing anti-predator behavior near chicks was mentioned both in studies of SOLOVIEV &amp; TOMKOVICH (1995) and SCt-mKKEI~'aAN &amp; VAN ROOMEN (1995). </p><p>Confirming the peak of body mass in incubating Little Stints and Curlew Sand- pipers, we also found it for Knots and Turnstones. The extra mass relative to brood- rearing of biparental incubators the Knot and the Turnstone (8.5 and 9.6 %, respec- tively) was smaller than that of spedes with a single incubating bird (12.3 to 15.0 %), which obviously have to spend more time on the nest. This provides an additional indirect support to the hypothesis about the compensatory nature of stores deposited by incubating birds. </p><p>SCHEKKERMAN &amp;; VAN ROOMEN (1995) found that the mass of Curlew Sandpiper females decreased as hatching approached. They lacked, however, weight data for the first half of the incubation period, which, probably, precluded revealing the curvilinear nature of mass variation within the incubation state, found for Little Stints, Curlew Sandpipers and Sanderlings in our study. Given the need to accumulate compensatory stores for incubation, a bird can hardly be expected to have a full stock at the very moment of completing the energy demanding process of egg-laying. The gradual increase of body mass during the first one or two weeks of incubation, probably, corresponds to the steady transition from one physiological condition to another. As the season progresses, environmental conditions (air temperature and food supply) improve, diminishing the need in energetic insurance, at one hand, while approach of hatching demands to reduce body mass in advance, at the other hand, that can explain a decrease of mass in the second half of incubation. The failure to reveal similar mass dynamics during incubation in Knots is, probably, connected to the fact that peak of mass is less pronounced in this species than in uniparental incubators. </p><p>The pronounced influence of phenologically unfavorable seasons on wader mass during the pre-nesting period seems natural, because birds have to spend much energy either on territory defense (males), or egg production (females) (t~CKLeFS 1974, ASHKENAZIE &amp; SAFRIEL 1979, GAV~tOV 1988). The first shorebirds of different species appeared from 6 to 10 June (median 8 June) in 'normal' years and from 10 to 19 June (median 12 June) in 'late' ones (based on the data from TOMKOVICH &amp; VRONSKY 1988a,b, TOMKOVICH &amp; VRONSKY 1994, TOMKOVICH et al. 1994), while the snow melting developed in 1992 with an approximate delay of 10 days, compared to 1991 (our data). This indicates lesser variation in arrival dates than in snow conditions, which may prevent feeding and breeding of birds at arrival in late seasons and make them wait for the appearance of snow-free patches, meanwhile depleting energy stores left after the flight from the last staging area. Poor feeding conditions at the beginning of reproduction may still affect the body mass during incubation, but by brood-rearing </p></li><li><p>M. Y. SOLOVIEV &amp; P. S. TOMKOVICH: Mass changes in waders 279 </p><p>a new generation of surface-active insects appears (MYERS &amp; PITELKA 1979, LANTSOV &amp; CHERNOV 1987), and food-shortage can no longer be connected with weather conditions at the start of the season. </p><p>The critical role of the pre-nesting period with its instability finds indirect evidence in the dynamics of numbers of the islandica subspecies of the Knot in Britain in January, that tended to be lower after cool Junes in the breeding range...</p></li></ul>