AUTUMN MIGRATION AND RECURRENCE OF THE THRUSH NIGHTINGALE LUSCINIA LUSCINIA

Tibor Cst)~G6*and Gabor L. LC)VElt*

SUMMARY.-Aurtrmn migration and recurrence ofthe Thrrtsh Nightingale Luscinia lusoinia at a stopover sire in Central Hunaarv. The mieration dvnamics and recurrence of the Thrush Nishtinsale Ltmcinia luscinia was studied ita stopover iite at 6c;a. central Hungary, between 1983 and 1993;~uring this time, a total of 293 brrds wen ringed. The migralion peaked on 19 August, with the main period kfwcen 8-30 Auaust. Adults did not seem to mi~rateahead of vouna birds. Reoeated rewotures oroved that the area war used lor stopover and premigr;tory fatlening.'~e ;ecapturcd '114 birds in416 &asms. I2 oithem after the date oithe last nnging. 24 September. The median stopover length was II days, the maximum 38 davs. There were no sianificant dillercnces in stooover lcneths throuehout mieration. 01all birds 6.1 % were recaplured aiter onc year or later; birds a&uing ea;ly and la& during-the migratton had higher probab~lttyof being recaptured in subsequent years. Thc proportton or birds with the maximum la1 score mcreased from 0% in earl\ Auaust to 33% bv midJeotcmber. Fat scores and body masses on arrrval were significantly higher in.btrd;arriuing aiter 50 ~ugu; than in those ringed earlier-~eanwing lenglhc of btrds, allhough gradually decreasing durmg the course olmigralion, did nor show sign~ficantchanges. Key words: Hungary, migration, recurrence, stopover, Thrush Nightingale.

RESUMEN.-Miyracidn otorial y recurrencia del Ruiseiior Combn Luscinia luscinia a una zona de descunso en Hunurfa Central. Se estudid la dinhifa migratoria y la recurrencia del Ruiseaor Com~n Lssciniu luscinia iuna zona de descanso en 6csa. ~ungrfa?entral,entrc 1983 y 1993. Durante cse liempo se an~llilron293 aves. La migraci6n alcanz6 el maximo el 19 dc agosto, con un perlodo cenlrrl enlre el X y 30 de acosto. No oarece sue 10s adultos iniciasen la migraci6n antes aue lor ibvencs. Las revetidas rccuper'cionn muistran que el Area era ulilizada como zoia de descanso y zona de engorde prem.igra~o- rio. Se rccapruraron 114 individuos en 416 ocusioncs dilerentes. 12 de ellas dcspuds del llltimo dla dc anillamiento. el 24 de seotcmhre. El ticmpo medio de parada iuc dc II dlas, Y el maximo 38 dlas No hub0 diierencias signilic&as entre las dishas etapas be descanso a lo largo he la migraci6n. El 6.1 % de las aves luc recuperado un aiio mas tarde, o m6s; las aves que llegaban al principio o al final del perlodo migratorio tenlan mas probabiiidad de ser recuperadas en aaos sucesivos. La proporcidn de aves con un actimulo miximo de grasa aument6 desde un 0%. a primeros dc agosto, hasta un 33 % a mcdiados de septiembre. Las reservas de grasa y la masa corporal a la llegada eran signilicativamente mayores en las aves que llegaban despugs del 30 de agosto cn comparaci6n con las anilladas con anterioridad a nta lecha. La longitud media del ala, aunque disminuye gradualmente durante la migra- ci6n. no mostr6 cambios signilicativos. Paiahrus clave: Hungrla, migraci6n. recurrencia, Ruiscaor ComBn, zona de descanso.

without considering stopover ecology, which is poorly known for many species (LOvei, Stopovers are necessary elements of inter- 1989). Descriptions of dynamics, stopover ti- continental bird migrations as most smaB mes and changes in body mass condition at passerines are not able to accumulate sufli- such sites can provide important information cient fat reserves to complete their migratory to understand migration strategies of indivi- journey without refuelling (Berthold, 1975; dual species (Ellegren, 1991). Studies of sto- Blem, 1980). Description and understanding pover sites at the edge of the range, where the of bird migration systems are not possible species only occurs during migration are es-

Dept. oi General Zoology. L. EQtv6s University. Puskin u. 3. H-1088 Budapest. Hungary. .' Horticultural Research Institute of New Zealand Ltd. Batchelar Research Centre. Private Bag 11030. Palmerston North 5301. New Zealand. Send repnnt request lo: G. LOvei. 58 AROEOLA 42UL 1995 pecially important as changes in the status of STUDYAREA AND METHODS species are frequently first detectable at the edge of the range (Lawton, 1993). The study site was in the 6csa Landscape The Thrush Nightingale (Luscinia lusci- Reserve, about 20 km southeast of Budapest, nia). a member of the thrush family, 1s a Hungary. The area is a marshland, with reed- medium-sized, insectivorous, ground-feedlag bed vegetation, meadows, bushes and forest intercontinental mtgrant, somewhat larger patches. This was similar to the birds' prefer- but closely related to the better-known Nigh- red habitat during breeding (Sorjonen, 1980; tingale L. megarhynclros (Cramp, 1988). The Cramp, 1988). From 1983-1993, birds were Thrush Nightingale prefers dense but patchy captured in mist nets, set up at standard mrst- vegetation, and moist, litter-covered ground; netting sites operating throughout the whole in central and southern Europe, this is found period of the study. A constant mist-netting in marshes, swamps and gallery forests. This effort was kept as much as possible. Mist net habitat selectivity seems to be retained du- operation was continuous between midJuly ring migration (Sorjonen, 1980; Cramp, and mid-September. Before and after this 1988). period, mist nets were operated for two-three The breeding range of the Thrush Nightin- days every week. Mist nets were controlled gale extends from 60'N to the line running every hour from dawn to dusk. The birds between the Carpathians, Balkans, Caucasus captured were removed from the nets and and the Central As~andeserts. Its eastern li- transported to the ringing station, where rin- mit is roughly 60'E. and its western limit ging and measurements were performed with- runs in a NW-SE direction, from Denmark in one hour after capture. From the data to the Carpathians (Harrison, 1982). Hunga- measured and registered, only capture date, ry lies at the western edge of the breedmg recapture status, age, fat score, body mass, range. Here the specles nests only in the gal- and wing length arc considered here. No bird lery forests in the northeastern part of the captured was moulting, except a few with country. Densities in northern Europe and replacement moult. These were excluded Russia can be high (Cramp, 1988). but are from the material evaluated. presumably low in Hungary (Schmidt, 1982). Ageing was based on criteria given in The species' wintering areas are in the East Svensson (1975) and subsequent editions. The African savanna region, between the Equator amount of subcutaneous body fat was esti- and 28"s (Moreau, 1972). In autumn, birds mated on a scale of 0 (no visible fat on the migrate southeastward to the eastern Medi- abdomen or in the furculum) to 5 (fat bulging terranean (Zink, 1975), enter Africa east of both on the abdomen and the furculum) 25"E then continue south towards their win- (Busse & Kania. 1970; Szentendrey el al., ter quarters (Cramp, 1988; Hogg er d., 1979). Body mass was measured with a Peso- 1984). la spring balance to the nearest 0.1 g. Wing Autumn passage at the Bosphorus lasts up length was measured by the maximal chord to late September. In Egypt, thrush nightin- method (Svensson, 1975). gales pass from mid-August to mid- October The seasonal dynamics of migration was (Cramp, 1988). In Sudan, the species is com- described by the Preston- equation (Preston, mon from the end of August until November 1966). This approach assumes that the migra- along the Nile (Hogg et al., 1984). In Hunga- tion curve follows a normal distribution. If ry, the first migrating birds arrive in the be- this assumption is correct, the curve of the ginning of August. with a migration peak du- cumulative catch VS. time falls on a straight ring the second half of August. A few birds line when drawn on probability paper. The are reported after middeptember (Schmidt, peak of migration is when the cumulative 1982). catch reaches 50% of the total. The main In this paper, we describe the dynamics of migration period is defined as the time bet- migration and the changes in wing lengths, ween the 15.9% and 84.1 % points on the body mass and fat reserves of the Thrush cumulative curve. These points enclose the Nightingale at a stopover site in Hungary, area of the normal curve-between its mean based on 11 years of data. and + 1 SD or 68.2 % of all data. AUTUMN MIGRATION AND RECURRENCE OF THE THRUSH NIGHTINGALE 59

Body mass and wing length measurements of adult vs. juvenile thrush nightingales. Luscinia luscinia, ringed at a stopover site, 6csa, central Hungary, 1983-1993. [Voiores de maso corporal (g) y longitud afar (wm) en aduNos y j6uenes dc Ruisetior Rmo, Luscinia luscina. anillados en uim zona de descariso ea bcsa (Hungrtu Ccnlrol). en el perlodo 1983-1993.1

Migration period [Perindo migrntorio] Early Pre-peak Post-peak Late [antes del8 [8-19 agosto] [%30 agosm] [despuis dd30 de agoslo] de agosro]

Body mas g Adult 2315~2.46(6)' 24.61 + 1.61 (16) 24.831 3.50 (23 21.461 5.67 181 Juvenile 23.97+1.80(37) 24.I8f 2.19 (93) ?3.90_+3.0?169) 27.44=5.17135) Wing lenglh. mm Adult 88.67i.1.97 161 88.35+3.32 (17) 88Mk2.27 (181 88.71 32.19 171 Juvenile 8913i. 1.79 (37) 88.34i.2.36 (871 8RR2 2.18 (621 RR.?5x2.37 132)

Data an mcans+one SD. (n). [* Lor dam represenlatt lo ntrdioidrsviaci6n esfnndw. (n)].

Due to the long time period of data collec- was ringed on 24 July and the latest one on tion, and the inevitable variation in trapping 24 September (birds stayed in the area later conditions, we divided the migration penod than this, see recaptures). During the I1 into 'early', 'pre-peak', 'post-peak' and 'late' years, 293 individual birds were ringed; 50 of periods, based on the Preston-diagram. All these were identified as adults. The migration subsequent evaluations were done following was unimodal w~thone migration wave only. th~sconvention. Age and/or sex classes may According to the Preston-diagram (Fig. I), follow different mtgration strategies (Alers- the peak of the migration was on 19 August tam, 1990). In thrush nightingales, however, and the main migratton period was between birds during mlgratton cannot be sexed by 8-30 August (23 days). Due to late migration external criteria (Svensson, 1975). Young and activity, the migration curve was skewed to old birds did not differ either in body mass the right (skewness, g, =0.487). New captures or in wing length (Table 1; G2 tests; body were somewhat concentrated around the ml- mass comparisons G2r8,2so=0.017- 1.236, gration peak, which made the curve lepto- all P>0.05; wing length comparisons kurtic, more peaked than a standard normal G2s,,=0.016-0.616. all P>0.05). Data for distributton (kurtosis, g, =0.117). old and young birds were therefore pooled. More adult birds were ringed during the Statistical analyses were done usmg the second than the first hall of the migration BIOM package (Rohlf, 1988) and the proce- (Table 2), which means that old thrush nigh- dures described in Sokal & Rohlf (1981). For tingales do not migrate ahead ol the juveni- fat score evaluation, medians rather than les. Mean wing lengths of the newly arrlved means were calculated (Hailman, 1965). Dif- birds slightly decreased during migration, ferences were tested by nonparametric me- from 89.1 mm during early migration (before thods. 8 August) to 88.3 mm during late migration (after 30 August, see Table 2). This difference was not significant (Tukey-Kramer tests, T- RESULTS K428s=0.343-2.264, all P>O.O5). The me- Migrmioti dynamics and niorphology dians were not dillerent either (89 mm, 88 mm, 89 mm, and 88 mm for early, pre- Thrush nightingales were not present at peak, post-peak and late periods, respectively). the site during the breeding season but were The shape of the wing length distributions regular during migration. The earliest bird (Fig. 2), however, indicated differences. Du- AROEOLA 4201 1995

7 Aug 17 ~ug 27Aug 6Scp 16 Sep MSep

FIG. 1.-Preston-diagram of the migration of the Thrush Nightingale at &a, central Hungary. The cumulative curve was generated from the numbers of newly ringed birds between 1983-1993. Arrows indicate the main mieration hod. [Diagramn de ~resron~arala'migraci6n del Ruiseflor Ruso en beso. Hungrla Central. Lo Ilnea acumulariua fue qenerada a parrir de las auzs onilladas enrre 1983 y 1993. Lusllechas indican el perlodo principal de la ring the early period (Fig. 2A), the distribu- me day recaptures excluded). Although the tion was skewed to the left: the range of wing latest migrant was ringed on 24 September lenghts was 83-94 mm, with the mean at (see earlier), 7 birds were recaptured on 12 89.1 mm. Wing lengths tended to be spread occasions after this date. The latest recapture out and not concentrating near the mean date was 8 October (in 1992). (platykurtic distribution). Before the migra- There were several between-year recaptu- tion peak (Fig. 2B), the distribution became res (Table 2), demonstrating faithfulness to skewed to the right and centered around the the stopover site. The longest period between mean (leptokurtic). During the post-peak ringing and recapture was 1463 days: this period (Fig. 2C), the distribution was similar- bird was ringed as a 1st year old on 3 Sep- ly right-skewed with even more values around tember 1983, and was recaptured on 5 Sep- the mean (leptokurtic). The wing length dis- tember 1987, with no in-between recaptures. tribution of late migrants (Fig. 2D) was qual- There were 5 other birds whose recaptures itatively similar to the early period but more spanned over three seasons (711-751 days skewed to the left and more spread out (slight between first and last captures) and 12 more platykurtosis). with recaptures in more than one autumn (intervals between recaptures between 345- 416 days). Altogether, 6.1 % of the birds rin- Recapture dynamics ged at 6csa were recaptured in later years. Birds at this site started gaining mass after Between 1983-1993, a total of 114 indivi- 2 days (LGvei & Csdrgb, manuscript); recap- duals were recaptured on 416 occasions (sa- tures after >3 days were therefore classified AUTUMN MIGRATION AND RECURRENCE OF THE THRUSH NIGHTINGALE 61

, , N; 2 '2 h 10 1 ,,A, 28 ,,u

4

82 & 06 88 90 92 94 O 82&18688909294 Wmg lmgh mm Wmg lmglh, m

FIG.2,Wing length distribution of newly ringed birds at 6csa. Hungary. 1983-1993. A) early migration. before 8 Aueust: B1 ore-oeak rninration.- 8-19 Auzust:- CI.. oost-oeak . miaration.- 20-30 Aueust:- D) late migration, akr 30 ;9Lgu;t. [Dtsrrihuc~drt de la longitud afar de aues anilladas en dcsa (Hungria). durunre el perindo 1983-1993. A) miaracidn temorona (antes del8 de aoosloJ:". BJ miaracidn anterior a1 oico mbximo miuratorio fenrre el 8-19 de"ugosto); 6) mi&cidn paslerior a1 pico m6xi& miyrotorio (enr;e el 20-30 de &sro); D) migraci6n rardlu (despub del 30 de agosro).] as 'true stopovers'. Following this criterion, than during the second half of the migration 86 individuals were 'true stopovers'. Some of per~od(Table 2). This is further underlined by these returned in several years, so we registe- the distribution oTminlmum stopover lengths red a total of 92 stopover periods. These (Fig. 4): although one third of the birds rin- birds were recaptured on 281 occasions ged during the early migration period was (Fig. 3). recaptured later, very few of these stayed lon- For within-season recaptures, the median ger than 20 days. In spite of this, 9.3 % of length of time between the first and last cap- them was recaptuted in later years. ture (if longer than 3 days) was 11 days Birds arrivtng late had a high recapture (SE= 1.2 days, n = 92). Differences in the 'mi- rate, d~dnot stay for shorter time than earlier nimum length of stay' were not significant recaptures, and more of them were recaptu- among the four groups of migrants (Kruskal- red in later years than for any other group Wallis test, H= 1.51, df=3, P<0.9). (Fig. 4D, Table 2). Migrants ringed durmg Birds arriving during the first half of mi- the peak period of migration had a lower gration had a lower probability of stopover probability of being recaptured in subsequent 62 ARDEOLA 42Il). 1995

28 Jul 07 Aug 17 Aug 27 Aug 06 Sep 16 Sep 26 Sep 06 Oct 11 Date

FIG.3.-Individual recapture histories of thrush nightingales recapturrd 23 days aner ringing at 6aa. Hungary, 1983-1993. Only within-season recaptures were included. [Recuperaciones de indiuiduos de Ruiserior Ruso quejiueron recaprerados mds de lres dfasdespuls de su ani- llamiento en 6csa (Hungrfa). en el perfodo 1983-1993. Sdlo se incluyen recupemciones intraesracionales.1 years (Table 2). This group showed no diffe- sed to 2 for the main migration period and to rence in their stopover characteristics with 3 (S.E.= 1.88, n=45) for birds ringed after 30 respect to other groups, yet few of them were August (Table 2). The frequency of birds with- recaptured in later years. out visible fat decreased, while the propor- tion of birds with fat scores of 4 and 5 increa- sed during the course of migration (Fig. 5). Body mass and fat reserve variation There was a pronounced difference m fat score distribution between the early and late mi- Average body mass on arrival changed little gration periods: during early migration, the during the first three periods but was higher frequency of scores 0, 1 and 2 was higher and during the late period of migration (Ta- the frequency of scores 4 and 5 lower than ble 2). The first three differences were not the corresponding frequencies for the late mi- statistically significant but migrants arri- gration period (Fig. 5). ving during the 'late' period had significant- Fat scores on arrival were significantly dif- ly higher body masses than birds arriving ferent from each other during the four migra- during earlier periods (Tukey-Kramer tests, tion per~ods(Kruskal-Wallis test, H= 16.83, T-K1.285=7.30 - 8.17, all P

Migration characteristics of the Thrush Nightingale. Lusriniu lusri~riu,at a stopover site at 6csa. cenlral Hungary. 1983-1993. [Curacterlsticm de lu nligrwi6n del Ruiseiiur Rrm. Luscinia luscinia. en lrno zona de descrurso en 6csu (Hurtqrfa Central) m el perlodo 1983-1993.1

Migration period [Perlodo migrurorio]

Characteristics Early Pre-peak Post-peak Late Time period ...... > 8 August 9-19 August 20-30 Augusl >30 August [Periudo de riempu] No. of newly ringed birds ...... 43 113 92 45 [Am unilludusj No. oladults (%) ...... 5 (11.6) 18 (15.9) 22 (23.9) 8 (17.8) [Addm r,'i,)] Body mass on arrival, g; meanf SD ...... 23.9k 1.9 24.2+2.1 24.1 k3.2 27.4k5.3 [Peso ul llegar. q: media fDT] Wing length*, mm; meanfSD ...... S9.1f 2.2 88.4k2.5 88.7k2.2 88.3k2.3 [Lonqitud ulur. mn~:media f DT] No. 01 birds recaptured aher >3 days (%) ...... 13 (30.2) 30 (26.5) 36 (39.1) 17 (37.8) [Aucs recupturadus desputs dc >3 dim (%)I No. recaptured in later years (%) ...... 4 (9.3) 6 (5.3) 2 (2.2) 6 (13.3) [Aues recoprurudns or 10s ~Wmosufios ((%)I Fat score on arrival; median* S.E...... 1 f0.3 2k0.2 2 _C 0.2 3k0.3 [Aclimulu de qrudu u Iu lleguda: mediunuf ES] Skewness ol la1 score distribution ...... 0.53 - 0.28 0.51 -0.38 [Sesgo en la disrrihucidn dc grasa] Kurtosis of la1 score distribution ...... - 1.05 - 0.94 -0.55 - 1.40 [Kurtosis en la distrihucidn tie grusaa] Min. length 01 stopover. days; medianfSE ...... Il f 2.1 13f 2.2 8 + 2.2 1223.1 [Duracidn mfn. de purudu. dhs: mediunuf ES

during the 'late' period was responsible for zation of the distribution: scores 1 & 2 de- the significant heterogeneity of the sample. creased dramatically, while scores 3-5 increa- This coincides with the results of the body sed; 33 % of birds had large fat reserves (sco- mass analysis (see abovc). re 5). The frequency of score '0' did not At the beginning of migration, almost decrease. 60 % of the ringed birds had little stored fat (classes 0 & 1). but 14 % of them had already accumulated substantial fat reserves (score 4). During the pre-peak migration period, the frequency of birds with medium fat reserves We caught no birds ringed at other sites increased sharply and constituted 63 % of all and none of the birds we ringed was caught birds (Fig. 5). There were fewer birds with elsewhere. The few existing foreign recoveries large fat reserves during the pre-peak period of thrush nightingales come from eastern than before 8 August. During the post-peak Germany, Denmark, Finland, and Belorussia migration period, the first birds with maxi- (Bird Migration Ofice, Hungarian Ornithol. mum fat reserves arrived (fat score 5). Soc., unpublished), leaving ample room to The fat score profile of birds ringed after speculate on the origin of the birds ringed at 30 August ('late' migration) showed a polari- our sites. The migration curve for central 64 ARDEOLA 4241). 1995

FIG. 4.-Minimum stopover lengths ol recaptured thrush nightingales at &a, Hungary, 1983-1993. A) early migration, before 8 August; B) pre-peak migration, 8-19 August; C) post-peak migrat~on,20-30 August; D) late migration, after 30 August. Stopover length is defined as the period between the first and last capture within one season. [Tienipo mlnimo de parada de ruiseflores rusos recaprurados en dm (Hungria), en el perlodo 1983-1993. A) miqracldn femorana (antes del8 de oqostoj: Bj m~aracrdnancerior 01 oico mdximo mioratorio lentre el 8-19 de agosro). C) migrocidn posterior 0.1 pic0 mdximo migrarorio (enrre &2V-30 de agosro); D) migracibn rurdia (despu4s del 30 dr agosro). El riempo de porada re define como el perfodo que transcurre enrre la primera y lo tiltima caprura denrro de una estacibn.]

Hungary was unimodal (Fig.1). suggesting man, 1985) and some species of wood war- only a single migration wave. In agreement blers (Parulidae) in North America (Hall, with available data on recoveries (Zink, 1981). 1975), we think that the birds we caught had he skewness towards longer-winged indi- come from breeding grounds in central Euro- viduals during the early migration period is pe, probably northwest of our study site. consistent with the interpretation that there The fact that old thrush nightingales did was an influx of longer-winged buds into a not migrate ahead of juveniles has been ob- shorter-winged, resident population. There served on arrival in Kenya (Cramp, 1988). are probably wing length differences among Other species with similar migration beha- sexes (Cramp, 1988). and similar differences viour include Willow Warblers Phylloscopus could exist between age classes as well as trochilus in the British Isles, where juveniles geographical populations. The timing of mi- migrate ahead of old birds (Norman & Nor- gration may also depend on the developmen- AUTUMN MIGRATION AND RECURRENCE OF THE THRUSH N~OHTINGALE 65

Fat score classes FIG.$.-Fat score distributions for thrush nightingales during autumn migration at baa, Hungary, 1983- 1993. early migration, before 8 August, n=43; B pre-peak migration. 8-19 August, n= 109: post-peak migration. 20-30 August, n=88; late migration. affer 30 Augusf. n=45. Only new captures are considered. . [Disrriblaidn del ocllrnub de grusu en el RuiseRor Ruso durunfe lo migracidn oroRal en 6csu (Hungrlu). en ei perfodo 1983-1993. O migracidn rempranu (anres d@IXde ugosto). n=43: a ntigracidn anterior a1 pico mdximo migraroriu (enrre el 8-19 de aqosfo). n= 109: migracidn posterior a1 pico mdximo migrarorio fenrre el 20-30 de agosro), n=88; miqrucidn rardfu (despub dcl 30 de agosto).n =45. Sdlo sc incluyen las nueuus capruras.] . tal and physiological condition of birds at 6csa. many species studied on migration which may vary between years and locations- in central Europe did not show clear trends more developed birds with longer wings may in wing length and only slight increases in migrate earlier. Of these possibilities, we can body mass during migration (Berthold el al., only exclude an influx of old birds with lon- 1991). ger wings. Differential migration between sex- The evaluation of the recapture periods is es is not documented for the Thrush Nightin- consistent with the hypothesis that birds arri- gale (Cramp, 1988; Zink, 1975). but we can- ving during the first half of the migration not exclude this possibility. During the late season were members of a breeding popula- period, the short-winged birds were possibly tion not far from our study site. This is sup- stragglers who were underdeveloped, but the ported by the low fat scores (60% of them oncoming autumn forced them to start mi- fell into classes '0' and '1'). If these would grating. Similarly to the thrush nightingales have been northern birds after the first bout 66 ARDEOLA 4211). 1995 of a long flight, they should have spent time cords are sparse and methods of calculating refuelling which they didn't. Feeding condi- stopover lengths vary. At a migratory stopo- tions, although not specifically measured, we- ver site in Sweden, the adults of the congener re expected to be better during the early part Bluethroat L. svecica spend an average of 3.7 of the migration season. We think that a si- days (maximum I1 days), while the juveniles multaneous increase of both low and high fat spend 4.46 days (max. 22 days; Ellegren, classes during the late migration period indi- 1991). In Germany and Austria, bluethroats cated the arrival of the first 'en route' nort- spend an average of 7 days, with a maximum hern migrants. of 2.5 weeks (Berthold et al., 1991). The ob- Birds arriving late regularly used the reser- served stopover length of the same species on ve as one of their refuelling sites, and, judging autumn migration in Israel is 3 days (SD=8 from the between-year recaptures, this group days; Lavee er al., 1991). Twenty-one other contained the most successful migrants. Mi- medium- or long-distance migrants stop over grants captured during the peak of the mi- for 1.2-4 days (Lavee et al., 1991). The ten- gration period may have used the area op- year Mettnau-Reit-lllrnitz program in central portunistically; however, they could also Europe found that many species stopped represent the normal fate of individuals be- over for varying periods. The overall mean longing to an edge population, with higher was 11.4 days and, contrary to our findings, mortalities than members of populations in the length of stopovers generally decreased the centre of the area of distribution. during migration (Berthold er al., 1991). Data The increase in 'fat score 1' during the late from Illmitz, Austria (which is the closest to period of migration could have arisen due to Ocsa), however, are the least reliable, due to two groups of birds: the arrival of those par- limitations of the trapping design (Berthold tially successful at an earlier stopover site, in et a!., 1991). They did not catch any Thrush search of a better fattening area, or the arri- nightingales, either. Bairlein (1988) reports a val of the first 'true migrants' from the north, maximum stopover of 20 days for the Reed who had, en route, partially depleted their Warbler Acrocephalus scirpaceus and 25 days reserves. The analysis of changes in body for the Garden Warbler Sylvia borin, two mass during stopovers can distinguish bet- transaaharan migrants, in northern Algeria. ween these two groups and is evaluated el- In an oasis in northern Egypt, Biebach et al. sewhere (LBvei & CsOrgo, manuscript). (1986) found median stopovers for the Lesser Late birds with no or minimal fat reserves Whitethroat Sylvia curruca of 4 days, maxi- (fat scores of '0' and '1') were, we assume, mum 17 days, and for the Willow Warbler stragglers: they had failed to accumulate suf- Phylloscopus trochilus, the median was 5 ficient fat reserves and it was too late at this days, the maximum 22 days. Sylviid warblers site to start: at least two of the main food in southern Spain stayed, on average, for 4-8 items, elderberry fruit and aphids, were past days (Hilgerloh, 1986). Most of these are their abundance peak (G. LBvei & T. Cs6rg6, shorter than our median or maximum values. personal observations). This would indicate However, these data mclude all birds captu- that about 3.8 % of birds (11 from a total of red and most do not make an attempt to 293) would eventually perish due to inade- distinguish between transients and true sto- quate fat reserve accumulation during the povers, so direct comparison is difficult. first phase of their journey. Two further caveats concerning our me- From the fat swre patterns during the four thods need to be discussed. Our estimation of main periods of the migration we conclude that the stopover period is conservative. We defi- birds in the first three main periods of migra- ned the period between first capture and rin- tion used the area as a premigratory fattening ging and the last capture as 'minimum stopo- area, while birds present during the late migra- ver length' as it is highly unlikely that every tion period were on stopovers for refuelling bird was captured on the first day of arrival. plus stragglers which were unable to follow a Likewise, the last capture does not necessari- 'typical' fattening and migration pattern. ly mean that the bird was not present later, The duration of stopovers is difficult to even if the mist-netting activity was conti- compare with other species and sites as re- nuous throughout the migration per~od.This AUTUMN MIGRATION AND RECURRENCE OF THE THRUSH NIGHTINGALE 67

is vividly illustrated by the bird with ring No. Foundation. Hungarian Nature Protection Guild, 992152 which was not recaptured between its Hungarian Credit Bank, The Independent Ecology ringing and subsequent recapture four years Centre, Budapest, and Earthwatch, Boston, U.S.A.. later. 6csa Migratory Bird Research Program, publica- tion no. 28. The second point of consideration is how representative are the fat class distributions in our samples. Our birds were collected by mist-netting, where capture results when a bird fails to notice the mist net in its flight ALERSTAM. T. 1990. Bird Migrulion. Cambridge path and gets trapped. This is a capture me- University Press, Cambridge. thod which depends on bird activity and the BAIRLE~N,F. 1988. Herbstlicher Durchzug. behaviour of birds has an unknown influence Kbrpergewichte und Fettdeposition von ZugvO- of capture probability. Not every encounter gcln in einem Rastgebiet in Nordalgerien. VnwL wurlr, 34: 237-248. with a mist net ends in capture but no quan- BERTHOLD,P. 1975. Migration: Control and meta- titative data are available on capture success bolic physiology. In D. S. Farner & J. R. King, or escape rate. Birds with dikrent fat reser- (Eds.): Aciun hioloy>~,Vol. 5, pp. 77.128. Acade- ves also have diflerent probabilities to escape mic Press. New York. danger (Witter & Cuthill, 1993). Fat birds are -. FLIEGE.G.. HEINE.G., QUERNER,U. & more prone to being captured as they are less SCHLENKER,R. 1991. Wegzug, Rastvcrhalten. able to manoeuvre in flight; on the other Biomelrie und Mauser von Klcinvbgeln in Mit- hand, they are probably less active than their teleuropa. Vogcl~torre.36 (Suppl.): 1-224. leaner conspecifics (Yong & Moore, 1993). BIEBACH,H., F~levR!cn, W. & HEINE,G. 1986. Interaction of bodymass, fat, foraging and sto- The former would result in overrepresenta- pover period in tmns-sahara migrating passerine tion of fat birds in the sample, the latter birds. Oecologiu, 69: 370-379. would tend to decrease their frequency of BLEM,C. R. 1980. The energetics of migration. In occurrence. The erect of these biases on our S. A. Garlhreux (Ed.): Animal miyrufion. nrienru- samples is not known. rion und noci!)urbn. pp. 175-224. Academic Press. Our data show that Thrush nightingales New York. used our site as a refuelling stopover point, Busst?, P. & KANIA.W. 1970. Ogeration Baltic. in spite of it being near the edge of their Polish Section. Methods. Acra Or~tirhokrgicu,12: breeding range. Such stopover sites are in- 231-267. (In Polish). CRAMP.S. (Ed.) 1988. Hundho,~k qf !Illre hirh <,j' dispensable for the Thrush Nighringale as Europe. rlre Milkdlr, Eusl und Nnrrh Apicu: rite the migration distance is too great to bridge birds of the Wesrer~Puleurcric. Vol. V. Tyrant it with one fat load (Zink, 1975). Continued flycatchers to thrushes. Oxford University Press. monitoring of migrating populations at sig- Oxiord. nificant stopover sites are important to as- ELLEGKEN,H. 1991. Slopovcr ecology of autumn sess the status of species. It would be of migrating Bluethroats Luainia s. scecico in rela- further interest to study the stopover beha- tion to age and sex. Ornis Scundinoaicu. 22: 340- viour of the species at a 'central' stopover 348. site, lo see if migration strategies and recur- HAILMAN,J. P. 1965. Notes on quanlitalive treal- mcnts of subcutaneous lipid data. Bird-Bunding. rence diner between 'central' and 'marginal' 36: 14-20. populations. HALL,G. A. 1981. Fall migration patterns of wood warblers in the southern Appalachians. Jnrmrd of Field Omhl~olngy.52: 43-49. AcKN0WLeDGEMaNTS.-We acknowledge the HARRISON,C. 1982. An Allus of ihe Birds qr the help of many volunteers who participated in the Wesrert~Pulumrcric. Collins. London. collection of data. We thank the Bird Banding HILGERLOH.G. 1986. Migratory behaviour in !he Ollice, Hungarian Ornithological Society, for un- southern Iberian Peninsula. In A. Farina (Ed.): published recapture information, Drs. H. Biebach, Proceedings ofrhe Is! Cor~fi.rcnceon Birds Winlr- P. J. Jones. J. H. Lawlon, E. 0.Minot, and C. J. rinu hr rhr !Medirerruneu~tRation. Rherriw di Veltman as well as G. Hilgerloh and an anony- ~i&,io rlellu Seluug~,ittn 10 (~'"ppl.):189-202. mous reviewer for comments on earlier drafts. HOSG. P.. DARE.P. 1. & RINTOUL,J. V. 1984. Field work over the years was supportcd by the Palaearctic mierants in the Central Sudan. ibis Hungarian Ornithologicsl Society, the Soros 68 ARDEOLA 4x0 199s

LAVEE, D., SAFRIEL,U. N. & MEILIJSON,I. 1991. SORJONEN,1. 1980. Selection of breeding habitat For how long trans-Saharan migrants stop over by the thrush nightingale Luscinialuscinia and its at an oasis? Ornis Scandinauica, 22: 33-44. position in bird communities. Ornis Scandinavi- LAWTON,1. H. 1993. Range, population abundance ca 11: 125- 134. and conservation Trends in Ecology & Evolution, SVENSSON.L. 1975. Identification Guide to Euro- 8: 409- 413. pean Passerines. Second edition. Natural History LWEI, G. L. 1989. Passerine migration between Museum. Stockholm. the Palaearctic and Africa. Current Ornithology, SZENTENDREY, G., Lbvat, G. & KLLAY,G. 1919. 6: 143-174. The qActio Hungancan bird ringing network. MOREAU,R. E. 1972. The Palaeorctic-Afiican Bird Working methods (In Hungarian) Allatrani Migration System. Academic Press. New York. KUzlerntnyek, 66: 161-166. NORMAN,S. C. &NORMAN,W. 1985. Autumn mo- W~rrEn,M. S. & CumlLL, I. C. 1993. The ecologi- vements of Willow Warblers ringed in the Bri- cal costs of avian fat storage. Philosophical Trm- tish Isles. Ringing & Migration, 6: 7-18. sactrons of the Royal Society of London Series 8, PRESTON, F. W. 1966. The mathematical represen- 340: 73-92. talion of migration. Ecology. 47: 375-392. ZINK,G. 1975. Der Zug europoeischer Singu(lge1. ROHLF,F. 1. 1988. BIOM. A package of statistical Vogelwarte Radolfzcll. programs to occon!pany the text Biometry. App- YONG,W. &MOORE,,F. R. 1993. Relation between lied Biostatistics, Inc., Setauket. New York. migratory activity and energetic condition SOKAL,R. R. & ROHLF,F. J. 1981. Biometry. Se- among thmshes (Turdinae) following passage cond edition. Freeman & Co. New York. across the Gulf of Mexico. Condor, 95: 934-943. SCHMIDT.E. 1982. Data on the autumn migration of the Thrush Nightingale (Luscinia lu~cinia)in Hunnarv. Maddrmni TdiPkoztatb 6: 171.172. fln [Recibido: 25.10.94j [Aceprodo: 11.4.95)