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27
ORNIS SVECICA 16: 27–33, 2006
Abstract
Introduction
Over the past decades many organisms have ad-
vanced the timing of spring events, most likely in
response to recent climate change (e.g. Stenseth
et al. 2002, Walther et al. 2002, Parmesan &
Yohe 2003). For instance, recent empirical work
has demonstrated changing phenology patterns
in the flowering of plant species (Fitter & Fitter
2002), in the emergence from pupae in insects
(Roy & Sparks 2000), and in earlier breeding
by amphibians (Beebee 1995) and birds (Crick
et al. 1997). Most ornithological studies demon-
strating temporal trends towards earlier spring
arrival or egg-laying dates have been carried
out in the temperate region of Europe and North
America (reviewed by Lehikoinen et al. 2004,
Dunn 2004), whereas only a few publications
Some migratory birds have advanced their spring arriv-
al to Northern Europe, possibly by increasing the speed
of migration through Europe in response to increased
temperature en route. In this paper we compare the
phenology of spring arrival of seven trans-Saharan mi-
grants along their migration route and test for patterns
indicating that migration speed varied over the season
using long-term data collected on the Italian island of
Capri and at Ottenby Bird Observatory, Sweden. There
was a linear relationship between median arrival dates
on Capri and at Ottenby. The slope was not significantly
different from one. On average, the seven species ar-
rived 15 days later at Ottenby compared to Capri. There
was a (non-significant) negative relationship between
the species-specific arrival dates at Capri and the dif-
ferences in median arrival dates between Capri and
Ottenby, possibly indicating a tendency towards faster
migration through Europe later in the season. To what
extent different species are able to speed up their migra-
tion to benefit from the advancement of spring events
is unknown.
Niclas Jonzén, Department of Theoretical Ecology,
Ecology Building, Lund University, SE-223 62 Lund,
Sweden. Email: niclas.jonzen@teorekol.lu.se
Dario Piacentini, Alessandro Montemaggiori and
Fernando Spina, Istituto Nazionale per la Fauna Sel-
vatica, via Ca’ Fornacetta 9, I-40064 Ozzano Emilia
(BO), Italy
Arne Andersson and Martin Stervander, Ottenby Bird
Observatory, P. O. Box 1500, SE-380 65 Degerhamn,
Sweden
Diego Rubolini, Dipartimento di Biologia Animale,
Università degli Studi di Pavia, piazza Botta 9, I-27100
Pavia, Italy
Jonas Waldenström, Department of Animal Ecology,
Ecology Building, Lund University, SE-223 62 Lund,
Sweden
Received 17 July 2005, Accepted 12 Jan 2006, Editor: D. Hasselquist
cover the Mediterranean region or Africa (e.g.
Peñuelas et al. 2002, Sanz et al. 2003, Gordo et
al. 2005). Thus, at present our understanding of
these patterns in migrant birds is somewhat bi-
ased towards the situation close to the breeding
areas, which makes it difficult to identify to what
extent arrival patterns in Northern Europe are
caused by processes in Africa or along the mi-
gration route through Europe.
One hypothesis to explain how tropical migrants
can advance their spring arrival to Northern Eu-
rope is that the migration speed through Europe
has increased, as suggested by e.g. Hüppop &
Hüppop (2003). A more rapid spring migration
in response to increased temperature en route has
recently been demonstrated in the Pied Flycatcher
Ficedula hypoleuca (Both et al. 2005). However,
the ability to speed up migration may be affected
The timing of spring migration in trans-Saharan migrants: a
comparison between Ottenby, Sweden and Capri, Italy
Vårflyttningens tidsmönster hos tropikflyttare: en jämförelse mellan Ottenby,
Sverige och Capri, Italien
NICLAS JONZÉN, DARIO PIACENTINI, ARNE ANDERSSON, ALESSANDRO MONTEMAGGIORI,
MARTIN STERVANDER, DIEGO RUBOLINI, JONAS WALDENSTRÖM & FERNANDO SPINA
28
by the “normal” speed of migration, which in turn
may vary across species.
In this paper, we compare the phenology of
spring arrival of seven trans-Saharan migrants
along their migration route by analysing long-term
data collected on the island of Capri, Italy, and at
Ottenby Bird Observatory, Sweden. By analysing
the relationship between arrival dates at Ottenby
and on Capri we tested for patterns indicating
whether migration speed varied over season. Late
migrating species may be more time constrained
than early migrating species, and they may there-
fore migrate faster.
Material and methods
Study sites
The island of Capri is situated c. 5 km off main-
land Italy, in the bay of Naples, with the trapping
site (40°33’N, 14°15’E) located about 400m above
sea level (Pettersson et al. 1990, Hjort 2006). In
spring, many migrating birds stop to rest, at least
for a short time (Holmgren & Engström 2006), on
this island after their passage over the Mediterra-
nean Sea. The trapping area on Capri lies mainly
within the perimeter of the walls of the old cas-
tle Castello Barbarossa and comprises c. 2 ha of
macchia vegetation typical for this region of the
Mediterranean. However, the plant species and
especially the structural composition of the veg-
etation has changed over the study period, most
dramatically by fires (the latest occurred in 1989),
which killed the larger pine trees and favoured
lower bush vegetation. This could potentially have
had an effect on the species composition of the
birds trapped, considering that different species
have different habitat preferences and the trapping
efficiencies of the nets may have changed.
On Capri data have been collected during 45
springs from 1956 to 2004 (no trapping in the pe-
riod 1982–1985), with the coverage varying from
13 to 89 days per season (Table 1). Birds were
trapped with mist nets throughout the study, but
the number of nets used varied considerably be-
tween, and sometimes also within, years. How-
ever, we could not take into account variation in
trapping effort in this study. The spring trapping
season on Capri is included in the Progetto Piccole
Isole, run by the Istituto Nazionale per la Fauna
Selvatica (Ozzano Emilia, BO) (Spina 2006).
Ottenby Bird Observatory (56°12’ N, 16°24’ E)
is situated at the southernmost point of Öland, a
137 km long island c.10 km off the coast of south-
eastern Sweden. The trapping area in the observa-
tory garden is 1.2 hectares and contains most of
the higher vegetation within the nearest 2 km. It is
surrounded by water on three sides and by grazed
meadows to the north. Birds have been caught at
Ottenby in funnel traps of Helgoland-type since
the first year of trapping in 1946, and mist nets
have been used since 1959. Since 1980 the num-
bers of nets and traps, their position and use in
spring have been strictly standardised. We consid-
ered data for 53 spring seasons from 1952–2004
as reliable for the purpose of this study. Details
on the data collection at Ottenby Bird Observa-
tory are given elsewhere, e.g. in Stervander et al.
(2005).
Species analysed
We have compiled data for seven of the most nu-
merously trapped bird species on Capri: Redstart
Phoenicurus phoenicurus, Willow Warbler Phyl-
loscopus trochilus, Icterine Warbler Hippolais
icterina, Garden Warbler Sylvia borin, Common
Whitethroat Sylvia communis, Spotted Flycatcher
Muscicapa striata and Pied Flycatcher Ficedula
hypoleuca. We have used ringing recoveries from
birds ringed on Capri and elsewhere in the Cam-
pania region (Naples, Sorrento, Amalfi; Scebba
(1993)), and recoveries of birds ringed at Ottenby
to sketch putative breeding areas, migration fly-
ways and possible wintering areas of the inves-
tigated species. An underlying assumption when
comparing arrival times between Capri and Ot-
tenby is that the species trapped belong roughly to
the same population.
Statistical analyses
We estimated the median spring arrival date for
each of the seven species. The estimated medians
were not dependent on whether we only analysed
data from years including ringing activity on both
Capri and at Ottenby, and we therefore decided to
keep data from all years. Due to the large samples,
any effect of variability in ringing activity within
and between seasons was effectively smoothened
out.
Because there are observation errors in both
the Capri and the Ottenby data sets we performed
a reduced major axis (RMA) to test whether the
relationship between median arrival on Capri and
at Ottenby differed from unity. RMA regression
minimize the product of the deviations from the
regression line across both the x (Capri) and the y
(Ottenby) variables.
29
Table 1. Ringing details and trapping data from Capri. No ringing in 1982–1985. Species: P.p. = Common
Redstart Phoenicurus phoenicurus, H.i. = Icterine Warbler Hippolais icterina, S.c. = Common Whitethroat
Sylvia communis, S.b. = Garden Warbler Sylvia borin, P.t. = Willow Warbler Phylloscopus trochilus, M.s. =
Spotted Flycatcher Muscicapa striata, F.h. = Pied Flycatcher Ficedula hypoleuca.
Fångsuppgifter från ringmärkningen på Capri. Ingen ringmärkning åren 1982–1985. Arter: P.p. = rödstjärt, H.i.
= härmsångare, S.c. = törnsångare, S.b. = trädgårdssångare, P.t. = lövsångare, M.s. = grå flugsnappare, F.h.
= svartvit flugsnappare.
Catch period Fångstperiod Number of birds ringed Antal märkta fåglar
Year Start Stop Days P.p. H.i. S.c. S.b. P.t. M.s. F.h.
1956 May 1 May 31 31 25 52 57 77 1 14 16
1957 Apr 1 May 30 60 164 320 227 445 69 125 88
1958 May 1 Jun 11 42 177 501 361 1248 26 339 54
1959 Apr 26 Jun 20 56 199 934 450 1305 53 664 264
1960 Apr 15 May 23 39 618 405 661 1327 235 347 539
1961 Mar 23 Jun 3 73 257 880 563 1472 89 880 286
1962 Mar 9 Jun 5 89 105 103 524 170 204 429 152
1963 Mar 24 May 31 69 196 436 330 683 135 578 343
1964 May 2 May 27 26 44 608 289 993 33 229 37
1965 Apr 14 May 27 44 178 420 451 557 378 203 138
1966 Apr 8 May 27 50 146 427 331 505 108 470 153
1967 Apr 11 Jun 7 58 286 368 240 384 257 194 355
1968 Apr 9 May 23 45 231 265 401 381 288 346 351
1969 Apr 1 May 25 55 197 213 408 163 384 294 180
1970 Apr 7 May 29 53 101 403 593 603 200 382 219
1971 Mar 24 Jun 5 74 140 195 305 223 140 300 144
1972 Apr 25 May 26 32 194 250 200 387 225 193 140
1973 Apr 8 May 26 49 89 403 178 266 101 327 114
1974 Apr 19 May 27 39 75 979 364 910 250 444 89
1975 Apr 11 Jun 2 53 160 374 401 546 124 722 261
1976 Apr 4 May 28 55 44 457 221 233 74 310 108
1977 Apr 19 May 23 35 94 149 188 206 70 241 110
1978 Apr 23 May 30 38 84 358 159 272 81 174 116
1979 Apr 14 May 23 40 108 624 368 666 282 58 183
1980 May 2 May 27 26 37 876 174 423 65 176 46
1981 Apr 15 May 23 39 88 485 171 180 97 195 174
1986 Apr 15 May 22 38 122 730 570 1113 273 474 465
1987 Apr 11 May 24 44 80 600 623 728 259 134 256
1988 Apr 16 May 23 38 41 366 185 237 125 280 176
1989 Mar 18 May 24 68 60 707 614 457 350 258 131
1990 Apr 5 May 23 49 95 757 902 614 197 572 465
1991 Apr 2 May 23 52 90 218 221 170 286 126 341
1992 Apr 5 May 22 48 69 798 419 350 364 538 188
1993 Apr 1 May 21 51 103 522 1105 748 433 324 453
1994 Apr 16 May 15 30 82 314 299 418 226 337 429
1995 Apr 17 May 15 29 81 236 314 302 241 199 357
1996 Apr 16 May 15 30 63 71 262 431 245 49 275
1997 Apr 16 May 15 30 185 334 519 367 422 291 358
1998 Apr 16 May 15 27 83 178 336 338 396 156 362
1999 Apr 16 May 15 29 79 451 448 876 321 245 286
2000 May 1 May 14 13 15 245 287 355 25 117 107
2001 Apr 16 May 15 27 119 79 314 284 457 298 497
2002 Apr 16 May 15 26 133 321 380 266 433 215 297
2003 Apr 16 May 15 30 74 876 320 487 317 260 566
2004 Apr 16 May 15 30 105 448 273 282 364 228 450
Total 1959 5716 19736 17006 23448 9703 13735 11119
30
Figure 1.
13
Figure 2
14
Figure 1. Map showing the recoveries of
Spotted Flycatchers Muscicapa striata ring-
ed or controlled at Ottenby (grey circles) and
Capri (black circles). The black stars indi-
cate the location of Ottenby and Capri. The
sample from Capri also includes recoveries
of birds ringed or recovered elsewhere in the
Campania region (from Scebba 1993).
Återfyndskarta för grå flugsnappare Mus-
cicapa striata som ringmärkts eller kontrol-
lerats vid Ottenby (grå cirklar) eller Capri
(svarta cirklar). De svarta stjärnorna anger
Ottenbys och Capris geografiska läge. Ca-
primaterialet inkluderar återfynd från hela
Campania regionen ( från Scebba 1993).
Figure 2. Map showing the recoveries of Ic-
terine Warblers Hippolais icterina ringed or
controlled at Ottenby (grey circles) and Capri
(black circles). The black stars indicate the
location of Ottenby and Capri. The sample
from Capri also includes recoveries of birds
ringed or recovered elsewhere in the Campa-
nia region (from Scebba 1993).
Återfyndskarta för Härmsångare Hippolais
icterina som ringmärkts eller kontrollerats
vid Ottenby (grå cirklar) eller Capri (svarta
cirklar). De svarta stjärnorna anger Otten-
bys och Capris geografiska läge. Caprimate-
rialet inkluderar återfynd från hela Campa-
nia regionen (från Scebba 1993).
31
Results
The ringing recoveries indicate that Spotted Fly-
catchers and Icterine Warblers (Figures 1 and 2)
passing Capri follow a central flyway in Europe
and Africa, and are later found in the general
direction of Ottenby. A similar pattern was also
found for Redstarts, Willow Warblers, Common
Whitethroats and Pied Flycatchers (not shown).
On the other hand, the recoveries of Garden War-
blers suggest a more eastern origin of the birds
trapped at Capri compared with those trapped at
Ottenby (Figure 3).
Figure 4 shows the linear relationship be-
tween median arrival dates on Capri and at
Ottenby for each species. The point estimate of the
slope was 0.87 (t5 = 8.45, P < 0.001), which is not
significantly different from one (95% confidence
interval: 0.61–1.14). On average, the seven spe-
cies migrated 15 days (0.79 SE) later at Ottenby
compared to Capri. In order to see if migration
speed varied over the season we tested if there was
a relationship between species-specific arrival
dates on Capri and the differences in median ar-
Figure 3.
15
Figure 3. Map showing the recoveries of Gar-
den Warblers Sylvia borin ringed or control-
led at Ottenby (grey circles) and Capri (black
circles). The black stars indicate the location
of Ottenby and Capri. The sample from Ca-
pri also includes recoveries of birds ringed or
recovered elsewhere in the Campania region
(from Scebba 1993).
Återfyndskarta för Trädgårdssångare Syl-
via borin som ringmärkts eller kontrollerats
vid Ottenby (grå cirklar) eller Capri (svarta
cirklar). De svarta stjärnorna anger Otten-
bys och Capris geografiska läge. Caprimate-
rialet inkluderar återfynd från hela Campa-
nia regionen (från Scebba 1993).
rival dates between Capri and Ottenby. There was
a non-significant negative correlation between the
species-specific arrival dates on Capri and the dif-
ferences in median arrival dates between Capri
and Ottenby (r = -0.57, P = 0.18; Figure 5).
Discussion
The strong and positive relationship between mi-
gration dates at Ottenby and on Capri suggests that
there are either common underlying environmental
factors affecting long-distance migrants along their
migration route, or that arrival dates are mainly
reflecting a specific endogenous time-programme.
In long-distance migrants, the onset of migration
is known to be under strong endogenous control
(Berthold 1996, Gwinner 1996), although the
speed of migration through Europe can be affected
by local conditions en route, as recently shown in
the Pied Flycatcher (Both et al. 2005).
The difference in median arrival date on Capri
and at Ottenby may indicate variation in migration
speed between species. We find that the Willow
Warbler, being the earliest migrant of the species
32
analysed, is also the species having the largest dif-
ference (19 days) in median arrival dates between
the two sites. In the same vein, late migrating spe-
cies such as the Spotted Flycatcher and the Icterine
Warbler show a difference of only 13 and 14 days,
respectively. However, the overall pattern is weak
even though some of the extremes are behaving as
expected. It would be interesting to know to what
extent the migration speed is limited by the time
needed to stop-over. A number of recent stud-
ies (e.g. Saino et al. 2004, Both et al. 2005) have
shown that arrival time is affected by environmen-
tal conditions en route, such that migration speed
increases when conditions en route are favourable.
If this is a general pattern the timing of migration
may not constrain adaptations to climate change
as much as previously thought (e.g. Both & Visser
2001, Both et al. 2005).
Competition for territories is an important fac-
tor affecting the timing of migration (Kokko
1999). A close look at Figure 4 shows that all
species falling below the regression line (i.e., mi-
grating faster than predicted by the linear model)
are using cavities as nesting sites. If cavities are
limited one may expect severe competition for ter-
ritories. In fact, comparative evidence indicates
that, among trans-Saharan migrants, hole-nesting
species migrate earlier than other species in the
Mediterranean (Rubolini et al. 2005). However, to
what extent different species are able to speed up
their migration to benefit from the advancement of
spring events is currently unknown.
Acknowledgements
This article is based on the efforts of many Swed-
ish and Italian ringers that have contributed to the
running of the long-term trapping series at Otten-
by and Capri. Although many people have been
involved on Capri, we would like to extend our
special gratitude to Carl Edelstam – the founder
of the station – and Jan Pettersson. We would also
like to thank the present and former staff of Villa
San Michele who has contributed significantly to
the study of bird migration on Monte Barbarossa
– thereby following the intentions of Axel Munthe.
N.J. is financially supported by the Swedish Re-
search Council. Finally, we would like to thank
Christian Hjort, Dennis Hasselquist and an anon-
ymous referee for constructive comments on an
earlier draft of this article. This is contribution no.
208 from Ottenby Bird Observatory, and results
from the Progetto Piccole Isole (I.N.F.S.): paper
no. 36.
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Sammanfattning
Klimatförändringar har gjort att många organis-
mers fenologi har tidigarelagts i norra Europa.
Flera tropikflyttande fågelarter anländer allt tidi-
gare och en förklaring till hur detta är möjligt är
att flyttningen genom Europa går allt snabbare då
vårtemperaturen ökar. Hur pass mycket olika arter
kan öka sin flyttningshastighet är okänt och borde
bero på deras ”normala” hastighet. I denna arti-
kel jämför vi datum för medianankomst på Capri
(Italien) och Ottenby (Sverige) på våren hos sju
arter som alla övervintrar söder om Sahara. Ring-
märkningsåterfynd visar att några arter (t.ex. grå
flugsnappare och härmsångare; Figur 1 resp. Figur
2) passerar Capri längs en central flyttningsväg
genom Europa och återfinns senare i riktning mot
Ottenby. Återfynd av andra arter ringmärkta på
Capri (t.ex. trädgårdssångare; Figur 3) pekar på ett
östligare ursprung än Ottenby. I Tabell 1 redovisas
fångstperioder och antal fångade fåglar under vå-
ren på Capri för de sju arter vilkas ankomsttider
analyseras i denna uppsats.
Jämför man medianankomst på Capri och Ot-
tenby (Figur 4) finner man att det är ett linjärt
förhållande med en lutning på 0.87 som dock inte
skiljer sig statistiskt från 1. I genomsnitt passerar
de sju studerade arterna 15 dagar senare på Ot-
tenby än på Capri. Det finns även en icke-signifi-
kant antydan till att ju senare en art flyttar desto
snabbare flyttar den genom Europa, att döma av
skillnader i medianankomst på Ottenby och Capri
(Figur 5). Det är okänt i vilken utsträckning olika
arter skulle kunna öka sin flyttningshastighet för
att dra nytta av vårens allt tidigare ankomst i norra
Europa. Det är därför viktigt att man studerar vil-
ka egenskaper som gör att en art har (eller saknar)
förmågan att anpassa sig till klimatförändringar.
