Blackwell Publishing Ltd.Movements by Juvenile and Immature Steller's

Ibis (2003), 145, 318–328

Blackwell Publishing Ltd.Movements by juvenile and immature Steller’s Sea Eagles Haliaeetus pelagicus tracked by satellite

MICHAEL J. MCGRADY,1* MUTSUYUKI UETA,2 EUGENE R. POTAPOV,3 IRINA UTEKHINA,4 VLADIMIR MASTEROV,5 ALEXANDER LADYGUINE,6 VLADIMIR ZYKOV,5 JACK CIBOR,7 MARK FULLER1 & WILLIAM S. SEEGAR8 1Forest and Rangeland Ecosystem Science Center, Snake River Field Station, Boise State University-Raptor Research Center, 970 Lusk St., Boise, ID 83706, USA 2Research Center, Wild Bird Society of Japan, 2-35-2 Minamiadara, Hino, Tokyo, 191-0041 Japan 3Institute of Biological Problems of the North, Russian Academy of Sciences, Magadan, Russia 4Magadan State Reserve, Portovaya St., 8, 685000 Magadan, Russia 5Department of Vertebrate Zoology, Moscow State University, 119899 Moscow, Russia 6Science Park, Moscow State University, Vorobyovy gory, 119899 Moscow, Russia 7Center for Conservation Research and Technology, University of Maryland Baltimore County, Room 105, TRC Building, 5200 Westland Boulevard, Baltimore, MD 21227, USA 8Soldier Biological and Chemical Command, Aberdeen Proving Ground, MD 21019, USA

Twenty-four juvenile Steller’s Sea Eagles Haliaeetus pelagicus were tracked via satellite from natal areas in Magadan, Kabarovsk, Amur, Sakhalin and Kamchatka. Nestling dispersal occurred between 9 September and 6 December (n = 24), mostly 14 September–21 October, and did not differ among regions or years. Most eagles made stopovers of 4–28 days during migration. Migration occurred 9 September–18 January, mostly along previously described routes, taking 4–116 days to complete (n = 18). Eagles averaged 47.8 km/day excluding stopovers; 22.9 km/day including stopovers. The mean degrees of latitude spanned during migration was: Kamchatka, 2.1; Magadan, 11.6; Amur, 7.3; and Sakhalin, 1.1. Eagle winter range sizes varied. Eagles concentrated in 1–3 subareas within overall winter ranges. The mean size of the first wintering subareas was 274 km2, the second 529 km2, and the third 1181 km2. Second wintering areas were south of first wintering areas. Spring migration started between 2 February and 31 March. Two eagles from Magadan were tracked onto summering grounds, well south of their natal areas. Both had early and late summering areas. One bird was followed for 25 months. It initiated its second autumn migration in the first half of October and arrived on its wintering grounds on 26 December. The second autumn migration covered 1839 km (20.9–22.4 km/day). Unlike its first winter when it used two subareas, this bird used only one subarea in 1998–99, but this was located near wintering areas used in 1997–98. It left its wintering ground between 13 April and 13 May, and arrived on its summering grounds between 7 June and 8 July. Unlike most satellite radiotracking studies, data are presented from a relatively large number of birds from across their breeding range, including new information on eagle movements on the wintering grounds and during the second year.

Steller’s Sea Eagles Haliaeetus pelagicus occupy a Sakhalin Island and the Kuril Islands (Babenko et al. limited breeding range along the seacoasts and rivers of 1988, Lobkov 1988, Nakagawa & Fujimaki 1988), eastern Siberia from Koryakland south to Ussuriland and on Kamchatka (Lobkov & Neufeldt 1986, (del Hoyo et al. 1994). Most winter on Hokkaido, Nakagawa et al. 1987). Food availability is probably an important factor *Corresponding author. inﬂuencing the distribution and movement of Steller’s Email: [email protected] Sea Eagles on the wintering grounds. Since the

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mid 1990s, the diet of Steller’s Sea Eagles win- from Toyo Communication Equipment Co., Ltd. tering in Hokkaido has shifted to include more (Toyocom) and Microwave Telemetry, USA were deer (Cervus nippon) carrion, perhaps as a conse- used. PTTs are programmed to transmit according to quence of declines in the availability of fish prey a set of duty cycles, which determine the rate of (WGWESE 1996, Nakagawa 1999). This has caused transmission, and in turn influence battery life. more wintering eagles to spend increased time Table 1 summarizes PTT duty cycle and longevity inland, especially later in the winter, enhancing their characteristics. All transmitters weighed about 65 g, exposure to potential lead poisoning through inges- and were attached as backpacks using Teflon ribbon tion of bullet fragments (Kim et al. 1999, Kurosawa (Dunstan 1972), incorporating a degradable link so 2000), which may threaten the long-term stability of that radios would fall free of the eagles. the population (Ueta & Masterov 2000). PTT location estimates were made using the ARGOS Steller’s Sea Eagle migratory movements have satellite system (http://www.argosinc.com/). Each been studied using direct observations (Nakagawa location estimate has an associated estimate of accu- 1999), colour marks (Ueta & McGrady 2000), and racy, the location class (LC), which is calculated by satellite-received transmitters (PTTs) (Meyburg & the system based on signal quality (LC Z, B, A, 0, 1, Lobkov 1994, McGrady et al. 2000, Ueta et al. 2000). 2, 3, in ascending order of accuracy). Only LC 0, 1, 2, We report the results of tracking Steller’s Sea Eagle and 3 were used in the analyses, and have estimated nestlings fitted with PTTs. Tracking Steller’s Sea accuracies of > 1 km, 1 km, 350 m and 150 m, res- Eagles via satellites is appropriate given the remote- pectively. Although it was necessary to use LC 0 ness of the areas they occur in and the large distances data to discern more detail in the movement of covered during migration (Fuller et al. 1995). The some eagles, this was done selectively, using only large number of transmitters used in this study those LC 0 location estimates that did not appear and the geographical spread over which they were to be outliers in relation to higher quality estimates deployed provide new information on individual occurring immediately before and afterwards, and and regional variation in migration and wintering only in cases where few higher quality data were behaviour. The long life of two tags gives information available. on movements of eagles in their first two years of Data were analysed using the ARCVIEW G/S life. Also, movements are detailed during winter in (Environmental Systems Research Institute, Redlands, Hokkaido where a threat of lead poisoning exists. CA, USA) and the Animal Movement extension designed for it (Hooge et al. 1999). The dispersal date was taken as the first day fledg- STUDY AREA, MATERIALS AND lings moved more than 3 km from the nest (LC > 0), METHODS and did not return. After dispersal, eagle locations Nestling eagles were radiotagged on Sakhalin Island, clustered at stopover sites, wintering areas and along the Amur River, near Magadan, and in the summering areas. These areas were defined by loca- central part of the Kamchatka Peninsula (Fig. 1). PTTs tion estimates that were clustered both spatially

Table 1. Details of PTTs ﬁtted to Steller’s Sea Eagle nestlings in 1997 and 1998.

No. of Life Year Region ID numbers PTTs Make Duty cycle (on/off) expectancy

1997 Magadan 11986-89 4 MW 8 h/48 h 1.5 years 23370-74, 28509-13 10 TC 6 h/12 h 6 months Kamchatka 03223 1 TC 6 h/42 h 1 year Amur 28515-17 3 TC 6 h/12 h 6 months 1998 Kamchatka 6749, 55, 62 3 TC 5 h/19 h 9 months 7317, 7641 2 TC 6 h/42 h 1 year Amur 6761, 7017, 18, 7101 4 TC 5 h/19 h 9 months 7102 1 TC 6 h/48 h 1 year Sakhalin 4131 1 TC 5 h/19 h 9 months

MW, Microwave Telemetry; TC, Toyocom.

320 M.J. McGrady et al.

Figure 1. Natal areas, migration paths and wintering areas of 24 Steller’s Sea Eagles tracked via satellite 1997–99. ‘?’ show areas outside the previously described wintering grounds where eagles were located, but for which we have incomplete data.

and temporally. Location estimates were mapped and earliest location, and was outside known wintering spatial clusters were identified when two or more grounds. locations from different duty cycles were collected Clusters identified over a period of 3 or more weeks within 3 km of each other. The earliest of these between October and March and within known win- became the centre of the site-defining circle. The tering grounds were categorized as wintering areas. stopover cluster was augmented by subsequent loca- Some eagles used more than one wintering area within tion estimates inside the circle within four days of the overall winter range. Locations of wintering areas the last estimate, and by estimates outside the circle were the harmonic means of clusters of location collected over less than 4 days, as long as they were estimates within the period of use. Summering areas followed by locations within the circle and within were defined and their harmonic mean locations 4 days. Once the cluster was identified, its location were determined in the same way as for wintering was the harmonic mean of all location estimates areas, but during April–September. within the time period. A cluster was categorized as Bearings between wintering areas and between a stopover place when collected during migration summering areas were determined in a Lambert Equal over at least a 4-day period from the date of the Area Azimuthal projection (Central Meridian 148°E,

Steller’s Sea Eagle movements 321

Latitude 52°N) by connecting the harmonic mean Dispersal and first autumn migration centres of the areas. Because distances between these were relatively small, they were measured as straight- Nestling dispersal occurred between 7 September lines. and 5 December (n = 24); 22 nestlings dispersed The date of migration was taken as the first day between 14 September and 21 October. Dates of that a move away from the natal, final summering or dispersal did not differ among regions. Sixteen final wintering area was made. Sequential move- eagles (including all nine reared on the coast) made ments between natal, stopover, wintering and sum- stopovers on estuaries and along large rivers during mering areas characterized migration. Arrival at migration, where they spent 4–28 days before con- stopover, wintering and summering area was the tinuing. The distance from nest to first stopover date of the location estimate upon which the original varied (Kamchatka: 22–196 km (n = 3); Magadan: site defining a 3-km radius circle was centred. 78–1547 km (n = 9); Amur: 72–242 km (n = 4); Because of the variance of the accuracy in location Sakhalin: 660 km (n = 1)). Three eagles made two estimates, sizes of wintering and summering areas stopovers; none made more than two. were described as 90% minimum convex polygons Eighteen eagles were followed to their wintering (MCPs). MCPs could include large areas that were grounds; most used previously described migration not used by eagles. routes (Fig. 1). In general, birds from Magadan, The distance of migration was calculated by join- Khabarovsk, Amur and Sakhalin migrated south ing location estimates along the route, then adding along the western edge of the Okhotsk Sea to together the lengths of the segments. Distances Hokkaido and the southern Kuril Islands, and birds between areas of activity (i.e. natal to stopover, stop- reared in Kamchatka moved into southern Kam- over to wintering, between different wintering areas, chatka, with some moving onto the Kuril Island and wintering to summering) were measured using chain late in winter. Two eagles marked in Magadan the harmonic mean locations of each of these activ- migrated ‘atypically’, one (ID 23374) initially moved ity areas as end points. west, then turned east, migrating to the Kamchatka In some cases either bird mortality or transmitter Peninsula. One bird (ID 11987) migrated to inland failure resulted in incomplete data on migration and China where it died. wintering by eagles. We truncated our data so that First autumn migration occurred between 9 for any behaviour by any individual (e.g. use of a September and 18 January (Kamchatka: 11 September wintering area by ID 11988) we were confident that (n = 5)–27 December (n = 4); Magadan: 9 September we had recorded all the locations related to only that (n = 12)–18 January (n = 7); Amur: 10 September individual and that behaviour. For example, for indi- (n = 6)–10 December (n = 6); Sakhalin: 14 viduals for which we did not record movement on September–23 November (n = 1)). Birds took 4– spring migration, we were not confident that all data 116 days to reach their initial wintering destinations. on the last wintering ground had been collected, and When actively migrating, eagles averaged a mini- those data were not included in our analyses. We mum of 47.8 km/day (sd = ±54.9, n = 17), and the excluded data from birds whose pattern of locations minimum mean rate of migration between natal and suggested that they had died, although their trans- final wintering locations (including stopovers) was mitters continued to function. 22.9 km/day (sd = ±10.7, n = 17). There was no significant difference between the migration rates of eagles from Magadan and Amur in 1997 (T = −0.55, RESULTS df = 8, P > 0.5), nor between birds from Kamchatka Twenty-eight nestling Steller’s Sea Eagles were fitted and Amur in 1998 (T = −0.19, df = 4, P > 0.8). The with PTTs in 1997 (17) and 1998 (11). Seventeen mean number of degrees of latitude spanned during eagles fitted with PTTs were reared in nests on rivers migration was: Kamchatka, 2.3 (sd = ±0.8, n = 4); and lakes; 10 eagles from Magadan and one from Magadan, 12.6 (sd = ±4.5, n = 7); Amur, 7.2 (sd = Sakhalin were from coastal nests away from large ±0.8, n = 6); and Sakhalin, 1.1 (n = 1). The rate of rivers or lakes. Twenty-four eagles provided data useful migration was related to degrees of latitude between in understanding postfledging movements, 12 from natal sites and harmonic mean of wintering range Magadan (∼58°N), six from Amur (∼52°N), five from (R2 = 0.616, df = 1, F = 24.06, P = 0.0002; Fig. 2). Kamchatka (∼54°N) and one from Sakhalin (52°N). The death of one bird (ID 11987), apparently Longevity of PTTs ranged from 47 to 759 days. from hitting electricity lines in north-east China on

322 M.J. McGrady et al.

Table 2. Size (km2) of wintering areas (90% minimum convex polygon) used by Steller’s Sea Eagles.

Wintering range

ID number (natal area) 1st 2nd 3rd

1997/98 23374 (M) 167 f 11986 (M) 1545 1822 11988 (M) 2185 850 3130 1998/99 7102 (A) 17 115 379 7017 (A) 324 f 7317 (K) 166 6749 (K) 57 32 34

f, transmitter failure; M, Magadan; A, Amur; K, Kamchatka.

Figure 2. Relationship between the rate of migration and degrees of latitude between nest and wintering grounds in 2 ± 2 ± Steller’s Sea Eagles. 274 km (sd = 595, n = 16), 529 km (sd = 700, n = 5), and 1181 km2 (sd = ±1697, n = 3), respectively (Table 2, Fig. 3). The two largest winter ranges were recorded for eagles whose tags were programmed for 10 November, was confirmed; the deaths of two longer life. other birds were strongly suspected. An eagle from The second wintering areas of juvenile eagles were Magadan moved to the Okhotsk River drainage south of the first wintering areas (n = 6). Five of six about 100 km from its nest, where it appeared to movements between first and second wintering areas survive into January, when the signal was lost. At this were in the first week of January. Two of three third time of year ice covers almost all of the Okhotsk wintering areas were south of the second wintering River, and we know of no records of successful over- areas. The dates of movement from second to third wintering of Steller’s Sea Eagles in this area. Also, wintering areas fell between early February and early after the birds flew 118 km to the coast soon after April. There was no tendency to move inland as win- fledging, locations from a transmitter fitted in Amur ter passed, but birds that started the winter on the showed no further movement, suggesting either that southern Kuril Islands moved to Hokkaido as winter the bird had died or that the transmitter had been progressed. dropped. Post-first winter movements First-year wintering areas Two birds from Magadan were tracked through Eighteen birds were followed to wintering areas. spring migration to summering grounds, which were For the most part, birds from Sakhalin, Amur and well south of their natal areas. Both had early and Magadan wintered on Hokkaido and the southern late summering areas (Table 3, Fig. 4). Kuril Islands. Eagles reared on Kamchatka wintered By the time of the second autumn migrations the on the peninsula with some moving onto the north- reception rate of location estimates had declined, ern Kuril Islands, especially late in winter. At least affecting the accuracy with which we could estimate one eagle from Kamchatka shared wintering grounds the dates on which events (e.g. migration) occurred, on Iturup Island (southern Kuril Islands) with eagles and the accuracy of locations of areas used by the reared in Amur that migrated through Hokkaido. eagles. Two eagles from Magadan left their first sum- Eagles could range widely, and focused on 1–3 mering grounds in late September/early October; of subareas when wintering (Fig. 3). For birds tracked these, ID 11988 was followed for 25 months in all. through the whole winter period (n = 2 (1997/98), As in its first autumn, it made stopovers along the 3 (1998/99)), one used one wintering area, one used migration path. Its second autumn migration lasted two, and three eagles used three subareas. The mean 76–88 days, and it arrived at its second-year winter- areas of first, second and third wintering ranges were ing grounds on 26 December, having covered

Figure 3. Winter movements by Steller’s Sea Eagles: (a) reference map; (b) areas (90% minimum convex polygons) used by Steller’s Sea Eagles wintering in Kamchatka; (c) areas (90% minimum convex polygons) used by Steller’s Sea Eagles wintering in Hokkaido.

Table 3. Summary of movements by Steller’s Sea Eagles in Geography and genetics may also affect migration their second summer. timing, route and location of wintering areas.

In this study, dispersal from natal areas occurred PTT ID Date of 11986 11988 spring migration 10 April 26 April 2–15 weeks post-fledging and did not differ from data of a single bird from Kamchatka (Meyburg & First summering area Lobkov 1994). Dispersal in Bald Eagles H. leucoceph- Arrival 25 June 24 June alus coincides with declines in prey availability, and Departure 17 July 10 July may be related to physical condition of the fledgling Harmonic mean location 55.2°N, 137.7°W 50.1°N, 144.1°W Degrees to natal area 4.2 5.6 (Wood et al. 1998). This situation is likely to be Degrees to wintering 12 10.5 similar in the Steller’s Sea Eagle, although details of Second summering area prey availability are not known for the areas where Arrival 1 August 25 August eagles were radiotagged. Departure 10 September 24 September Stopovers were a feature of first-autumn migra- Harmonic mean location 57.1°N, 138.8°W 54.5°N, 136°W Degrees to natal area 2.3 5 tion by Steller’s Sea Eagle, especially for eaglets Degrees to wintering 14 11.2 reared on the coast. Stopover sites were on large rivers and estuaries. These sites were usually south of,

or at least at a latitude similar to, their natal places, although the nestling whose natal area was farthest south (Sakhalin) initially moved north. The fact that 1839 km (20.9–22.4 km/day). Unlike winter 1997/ most rivers in the region, and on which eagles were 98, this bird used only one wintering area in the winter marked, flow east or south probably enhanced this of 1998/99, although the areas used in different tendency. The use of stopover sites by eagles was winters were close to one another. It left its winter- probably related to prey availability, and departure ing ground between 13 April and 13 May, and from these may have been associated with declining arrived on the summering grounds between 7 June food availability as a result of reduced migration of and 8 July. Areas used during this second summer salmonids and perhaps increases in ice and snow after fledging were closer to its natal area than those cover. The late autumn distribution of Haliaeetus used in the summer following fledging (Fig. 5). eagles on Hokkaido is related to the abundance of salmon (Ueta et al. 1999). Although we saw no significant variation in the timing of migration among DISCUSSION regions, within-year sample size was low, and eagles Location estimates calculated by the ARGOS sys- reared in areas where sea and river ice forms earlier tem vary in accuracy, and sample sizes are sometimes in the year may migrate earlier. small because high-quality locations form only a The pace of migration appeared to be related to proportion of all estimates. PTT quality, latitude, the proximity of the natal area to the wintering battery characteristics and erroneous assumptions grounds, especially if this is measured by distance about the altitude of the PTT can cause variation in travelled rather than degrees of latitude covered, but the proportion of high-quality locations. In addition, may also have been affected by variations in weather some behaviours (such as short stopovers by eagles conditions in late autumn and early winter. From our or short forays away from wintering areas) might not data it is difficult to separate weather and regional be documented because PTTs do not provide data effects. continuously. Despite these factors, which contrib- In general, eagles migrated southward along ute to an effective reduction in the amount of usable known migratory routes, with eagles reared west data, and which sometimes limit their interpreta- of the Shelikhov Gulf moving west around the tion, PTTs are an effective tool in describing gross Okhotsk Sea, and birds reared in Kamchatka winter- movements of eagles (Fuller et al. 1995, Britten et al. ing in the south of the peninsula and on the Kuril 1999). Island chain. The ‘atypical’ migration routes used by Food supply plays some part in determining two birds reared in Magadan were to inland China whether birds migrate, and where they spend the and to Kamchatka. For the individual that went to nonbreeding period (Newton 1979), and the move- Kamchatka, only one location between the breeding ments recorded for Steller’s Sea Eagles are probably and wintering grounds was estimated (LC 0). This responses to prey availability and perhaps to weather. was located in the middle of the sea, which suggests

Figure 4. First spring migration and ﬁrst summering areas of Steller’s Sea Eagles reared in Magadan.

Figure 5. Movements of a Steller’s Sea Eagle tracked 22 July 1997 – 20 August 1999. Solid line: summer 1997 – summer 1998, broken line: summer 1998 – summer 1999.

that the bird made a sea crossing. The shortest cross- By late March most eagles have left the wintering ing would be about 730 km. Although one would grounds in Hokkaido (Nakagawa et al. 1987). The not expect a Steller’s Sea Eagle to migrate over such paths of northward migrating juvenile Steller’s Sea a large stretch of open water, raptors sometimes land Eagles tracked by us were similar to migration routes on oceangoing ships, and this might have been the recorded for Steller’s Sea Eagles of various ages (Ueta way in which such a crossing was made. Southward et al. 2000), and similar to part of the route used by migration by some Steller’s Sea Eagles marked in adult White-tailed Sea Eagles (Ueta et al. 1998). Kamchatka followed the routes used by a nestling The fact that juvenile eagles did not return to their Steller’s Sea Eagle tracked in 1991 (Meyburg & natal areas is not surprising. Several other raptor spe- Lobkov 1994) and two adult White-tailed Sea Eagles cies that mature only after a number of years do not H. albicilla in 1995 (Ueta et al. 1998). This reinforces show fidelity to their natal areas prior to maturation the findings from other studies showing that not all (e.g. Golden Eagle Aquila chrysaetos, Haller 1996). eaglets reared in Kamchatka winter on Kurilskoye In general the locations where juvenile eagles sum- Lake for the whole of the winter (Lobkov & Neufeldt mered have low breeding densities of Steller’s Sea 1986, Meyburg & Lobkov 1994). However, the high Eagles, and are characterized by few cliffs or big trees numbers of wintering eagles counted on the lake, for nesting, few large rivers, and lingering sea ice in and the fact that some of the eagles fitted with PTTs the spring. Because adult eagles defend the breeding spent part of the winter there supports the view territory, juvenile eagles may summer in areas of low that it is important for at least some of the winter. eagle breeding density to avoid conflict. Furthermore, the behaviour of ID 23374 suggests In general, these data support what is known about that not all birds wintering in Kamchatka are from Steller’s Sea Eagle movements from direct observations there. and other satellite-received radiotelemetry studies. The sizes of winter ranges were sometimes derived In terms of conservation these data highlight the im- from a small number of location estimates, and may portance of stopover areas on large rivers, implying have been affected by the inaccuracies in location that late summer runs of salmon are important. On estimation. These data should therefore be used to the wintering grounds in Hokkaido eagles can spend generate hypotheses for future testing rather than significant amounts of time inland, where they are accepting them as full descriptions of eagle move- exposed to the threat of lead poisoning from carcasses ments. Although some eagles seemed to move very left by hunters, but coastal areas are also important little once they arrived on the wintering grounds, as feeding areas in winter. In light of these data and others seemed to range widely, and some used more the vulnerability of the population, it is important that than one area during the course of the winter. The conservation action continues to be aimed at conserving reports of eagles spending the early part of the win- food supplies throughout the range, and reducing the ter in coastal areas, then moving to inland areas potential for lead poisoning, particularly on Hokkaido. (where deer carrion is available, Ueta et al. 2003) were not confirmed by the satellite tracking data L. Schueck, M. Bramer and S. Caquelin managed the but, especially in late winter, some eagles ranged ARGOS data. Funds for fieldwork and processing of over inland areas. The distribution of Steller’s Sea data from Magadan were supplied through Edgewood Research and Development and Engineering Center, Eagles in autumn and winter in Hokkaido has Aberdeen Proving Grounds, Aberdeen, USA. The Institute been linked to the distribution and availability of for Wildlife Studies and Chugach National Forest pro- prey. Important fish species include Chum Salmon vided support in the field in Magadan. NEC Corpora- Oncorhynchos keta (Ueta et al. 1999, Shiraki 1996), tion provided funding to the Wild Bird Society of Walleye Pollock Theragra chalcogramma, Pond Japan; NTT donated the Toyocom PTTs. 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