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A comparison of two methods for monitoring migrating broad-winged Raptors approaching a long water crossing

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Observations on raptor migration were carried out at the island of Marettimo (Central Mediterranean) during the first half of October 2007. Raptors concentrate at this site before crossing the Channel of Sicily en route to Africa (130 km). We used and compared two different census methods in order to limit the problem of double-counting of migrating raptors. A total of 510 and 299 individuals were respectively counted using two different methods: the first one is the standard method in use to count migrating raptors (all-occurrence), the second one consists in considering the maximum number of raptors observed together for each observation day (maximumdaily-count). Raptors observed were almost juveniles and immatures (inexperienced individuals). For short-toed snake eagle Circaetus gallicus, booted eagle Aquila pennata and common buzzard Buteo buteo, the results show significant differences in counts. Weather conditions affected observed numbers of these species at the site, although they did so similarly for both methods. Results show that, at Marettimo, it is not possible to make an accurate count of inexperienced broad-winged raptors approaching the long water crossing. For this reason we suggest to consider as an activity index the daily count of the maximum number of birds of the same species observed together during each day of field work.
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inexperienced and/or young individuals (Agostini 2005,
Agostini and Malara 1997, Agostini et al. 2000, 2004a,
2004b, 2005).
 Whenaraptorfacesopenwater,severalfactorsinu-
ence its decision of whether or not to attempt a crossing:
the morphology, the distribution of landmarks and lead-
ing lines, the length of the water crossing, the physiologi-
calconditionofthebird,ockingbehaviour,timeofday,
and previous experiences; moreover, weather conditions
strongly affect water crossing behaviour (Kerlinger 1985,
1989, Agostini et al. 1994, 2002, 2003, 2005, Agostini
and Duchi 1994, Agostini and Panuccio 2003a, 2003b,
Klaas sen et al. 2010, Meyer et al. 2000, 2003, Panuccio
2005, 2011, Thorup et al. 2003). Thus, it is not surpris-
ing that at some sites, accurately counting migrating rap-
torsapproachingawatercrossingcanbedifcult;indeed,
in such cases Accipitriformes sometimes interrupt migra-
tion, disappear from view and pass again through the study
siteafterseveralhours.Raptorsockssometimeshesitate
and split up when faced with a water crossing and some-
timesyintheoppositedirectionofmigration(Bildstein
et al.2007).Becauseofthisbehaviourmanycoastalare-
INTRODUCTION
During migration Accipitriformes mostly use soaring
ight, thus optimizing the use of thermal currents, and
avoidinglongwatercrossingtolimitpoweredightover
water and to reduce energetic costs (Kerlinger 1989). The
wing morphology of raptors plays a role in the evolution of
migration strategies; in particular, species with relatively
broad wings (low aspect ratio) are less suited to undertake
the crossing of large bodies of water while the same, heav-
ier,speciesmaximizetheirightspeedoverland.Inpar-
ticular Kerlinger (1989) proposed the aspect ratio [(Wing
Span)2/(Wing Area)] as one of the most important mor-
phologic features explaining water crossing tendency of
raptors, while other authors highlighted the weight differ-
ences(SpaarandBruderer1997,ÅkessonandHedenström
2007, Pennycuik 2008). As a result, large soaring raptors
likevultures,eagles and common buzzardsareobserved
in small numbers during spring and autumn migration in
Central Mediterranean. Observations of broad-winged
raptorsinthis area donotgenerallyreectthe existence
ofatruemigrationyway,butrathertheymostlyconcern
A comparison of two methods for monitoring migrating
broad-winged Raptors approaching a long water crossing
Michele Panuccio¹,², Marco Gustin³, GiusePPe BoGliani¹
¹ Università di Pavia, Dipartimento di Scienze della Terra e dell’Ambiente - Via Ferrata 1, 27100 Pavia (Italy)
(panucciomichele@gmail.com)
² MEDRAPTORS (Mediterranean Raptor Migration Network) - Via Mario Fioretti 18, 00152 Rome (Italy)
³ LIPU (Lega Italiana Protezione Uccelli) - Via Trento 49, 43122 Parma (Italy)
Abstract–ObservationsonraptormigrationwerecarriedoutattheislandofMarettimo(CentralMediterranean)duringthersthalfof
October 2007. Raptors concentrate at this site before crossing the Channel of Sicily en route to Africa (130 km). We used and compared
two different census methods in order to limit the problem of double-counting of migrating raptors. A total of 510 and 299 individuals
wererespectivelycountedusingtwodifferentmethods:therstoneisthestandardmethodinusetocountmigratingraptors(all-occur-
rence), the second one consists in considering the maximum number of raptors observed together for each observation day (maximum-
daily-count). Raptors observed were almost juveniles and immatures (inexperienced individuals). For short-toed snake eagle Circaetus
gallicus, booted eagle Aquila pennataandcommonbuzzardButeo buteo,theresultsshowsignicantdifferencesincounts.Weathercon-
ditions affected observed numbers of these species at the site, although they did so similarly for both methods. Results show that, at Ma-
rettimo, it is not possible to make an accurate count of inexperienced broad-winged raptors approaching the long water crossing. For this
reason we suggest to consider as an activity index the daily count of the maximum number of birds of the same species observed together
duringeachdayofeldwork.
13
Avocetta 35: 13-17 (2011)
Panuccio et al.
as(likeCapBonPeninsula,MountConero,CirceoProm-
ontory), were previously considered unsuitable for count-
ing migrating raptors (Agostini 2005, Agostini et al. 1994,
Agostini and Duchi 1994, Agostini and Panuccio 2003a,
2003b, Panuccio 2005, Panuccio et al. 2004, Premuda et
al. 2008).
 ThedistancebetweenAfricaandItalyisnarrowestat
the Channel of Sicily between the island of Marettimo and
theTunisianpeninsulaofCapBon;inthisareathousands
of migrating raptors are regularly observed during autumn
(Agostini et al.2000,2004b).Inparticular,betweenmid-
August and the end of September large numbers of black
kites Milvus migrans,honeybuzzardsPernis apivorus and
marsh harriers Circus aeruginosus are observed. Later in
the season, a smaller number of raptors, mostly juvenile
short-toed snake eagles Circaetus gallicus are recorded
(Agostini et al. 2004a, 2005).
The aim of this paper is to verify whether it is possible
to make an accurate count of large soaring raptors migrat-
ing through the island of Marettimo en route to Africa, and
to compare two different methods for doing so.
STUDY AREA AND METHODS
The island of Marettimo (Fig. 1) is located 30 Km off
WesternSicilyand130KmNEoftheCapBonPeninsula
(Tunisia). Observations were made from the 3rd to the 15th
October 2007 using a single watch point located along the
main ridge of the island at an elevation of 500 m above sea
level. Two observers with binoculars and telescopes were
employed. Observations were made from 9:00 (solar time)
until dusk.
Two different methods were used to count raptors.
Therstmethod isthestandard oneinobservationstud-
ies(Bibbyet al. 2000,Bildsteinet al. 2007) and hereaf-
ter called “all-occurrence”: it consists in counting raptors
when they passed over the watch point; in order to avoid
counting them again, birds were followed with binoculars
andtelescopeinordertoensureindividualsandocksre-
allywereleavingtheisland.Raptorsobservedyinginthe
opposite direction of the presumed optimal migration were
notconsideredin thecount(Bibby et al. 2000, Panuccio
2005).
The second method, hereafter called “maximum-daily-
count”, consists to count the maximum number of individ-
ualsofthesamespeciesobservedtogetheroneachday.In
both cases, we noted whether any individual birds could be
identiedbyplumagepeculiarities;moreover,birdsroost-
ing at the site were counted only if they were not observed
the following morning.
We tested the hypothesis that local weather conditions
affect the count of migrating raptors. We considered the
daily counts of the three species that show signicantly
different results with the two census methods: the short-
toed snake eagle, the booted eagle Aquila pennata and the
commonbuzzardButeo buteo.AGeneralizedLinearMod-
el (GLM) with negative binomial distribution was applied
using as independent factors: i) wind direction, ii) wind
speed (km/h), iii) temperature (°C), iv) air pressure (mbar)
and v) humidity (%) to explain variation in daily counts
of each species. These variables were obtained from the
meteorological station of the Trapani Airport every day at
13.20. Wind direction was divided into two categories ac-
cording to the most common winds in the study period:
northerly and southerly winds. The GLM was repeated
with the results of both census techniques. A Spearman
test was run to avoid collinearity between the 5 variables;
air pressure was excluded from the analysis since it corre-
lates with wind direction (Rho=-0.63; P<0.05). We veri-
edthestatisticalpowerofeachGLMbyapplyingaSha-
piro-Wilktestontheresidueofthemodel.Itwasnonsig-
nicantinallcases(P>0.05).
14
Figure 1.Study area(M=IslandofMarettimo,CB =Cap Bon
Pe ninsula, CP = Circeo Promontory, MC = Mount Conero).
150 km
N
MC
CP
CB
M
Sicily
Tunisia
A comparison of two methods for monitoring migrating broad-winged Raptors
15
RESULTS AND DISCUSSION
During the entire survey, we counted 510 raptors with the
“all-occurrence” method and 299 with the “maximum-dai-
ly count” method, for a total of 12 species (Tab. 1). For
comparisons involving more than 10 birds, the differences
incountsbetweenthetwomethods appear to be signi-
cantforthreespecies:theshorttoedsnakeeagle(χ²=22.2,
d.f.1,P<0.01),thecommonbuzzard(χ²=41.2,d.f.1,P<
0.01)andthebootedeagle(χ²=5.9, d.f. 1, P< 0.05). For
the marsh harrier, the black kite and the honey buzzard
thedifferencesarenotsignicant,but onlyfewindividu-
alsofeachwereobserved.Broad-wingedraptorshesitated
infrontof thewatercrossingand infourcasesocks of
shorttoed snake eagles and common buzzards were ob-
servedying east towards Sicily, while eagles wereob-
served undertaking the water crossing toward Africa in on-
ly three cases.
 Forall these three species, weather conditions inu-
enced the number of individuals recorded, to a similar ex-
tent for both census techniques (Tab. 2). Wind speed in
the case of short-toed snake eagle and booted eagle and
winddirectioninthecaseofcommonbuzzardstronglyaf-
fectedobservednumberofmigrants.Inparticular,within-
creasing wind speeds numbers of short-toed snake eagles
and booted eagles decreased, while with southerly winds
(head-winds) lower numbers of common buzzards were
recorded. These results are expected, since raptors tend
to avoid water crossings when wind conditions require
an extra amount of energy consumption, as such as when
strong winds or headwinds are blowing (Meyer et al. 2000,
2003, Panuccio 2011, Panuccio et al.2002).Inthecaseof
short-toedsnakeeaglesand common buzzards, observed
numbers were also positively correlated with tempera-
tures; however, since temperature decreased as the days
passed (Rho=-0.72; P<0.01), we suggest that this corre-
lation could be related to the migration timing of the two
species.Resultssuggestthatweatherconditionsinuence
daily counts similarly for both methods probably because
raptors do not reach the island of Marettimo with unfa-
vourable wind conditions, as in these cases they do not un-
dertake the short water crossing between Sicily and Maret-
timo (approx. 30 km).
Previous studies which were carried out at the same
site showed that other species of Accipitriformes, such as
blackkites,honey buzzards, egyptianvulturesNeophron
percnopterus and marsh harriers were more likely to un-
dertake the water crossing en route to Africa (Agostini
et al. 2000, Agostini et al. 2004b, Ceccolini et al. 2009,
Panuccio 2005). Different behaviours also reect differ-
entmigrationstrategies:indeed,themigrationywaysof
those species pass over the Central Mediterranean area
and the island of Marettimo. On the other hand, short-toed
snakeeagles, bootedeaglesandcommonbuzzardsrarely
cross the central Mediterranean, preferring to use alterna-
tive yways or wintering mostly in Europe (Agostini et
al. 2000, 2004a, 2005, Agostini and Malara 1997, Isen-
mann et al. 2005). Additional support for the above hy-
pothesis comes from an analysis of the age classes of birds
observed in the present study, which were mostly young,
inexperienced individuals (Tab. 3).
This study shows that at the island of Marettimo it is
better do not use the same census method for all species of
migrating raptors. Since an accurate count of raptors mi-
Table 1. Numbers of raptors counted by two census methods.
SPECIES
Short-toed snake eagle Circaetus gallicus
BootedeagleAquila pennata
Lesser spotted eagle Aquila pomarina
Bonelli’seagleAquila fasciata
Egyptian vulture Neophron percnopterus
CommonbuzzardButeo buteo
HoneybuzzardPernis apivorus
BlackkiteMilvus migrans
Marsh harrier Circus aeruginosus
HenharrierCircus cyaneus
Pallid harrier Circus macrourus
Circus pygargus/macrourus
TOTAL
ALL-OCCURRENCE
210
44
10
1
1
144
11
33
51
2
1
2
510
MAXIMUM-DAILY-COUNT
123
23
6
1
1
53
10
32
44
2
1
2
299
Panuccio et al.
16
grating through Marettimo is unrealistic, we suggest that
broad-winged raptors should be “counted” by considering
the maximum number of individuals of the same species
observed at the same time on each day. Since recent stud-
iesusingsatellitetrackingshoweda highdegreeofex-
ibility between different individuals and years (Mellone et
al. 2011, Vardanis et al. 2011), we cannot exclude that the
proposedcensus techniquecouldalsobeawed andbias
the data. For this reason, this method should be seen more
as an “activity index rather than an actual estimate of the
numbers of individuals passing through”(Bildstein et al.
2007) the island of Marettimo, mainly considering that an
accurate count is not possible in the case of inexperienced
broad-winged raptors approaching a long water crossing.
Acknowledgements – This study has been made on behalf of the
LIPUBirdLifeItaly(LegaItalianaProtezioneUccelli).Wewould
liketothankAntoninoProvenzaandVitoVaccarofortheirhelp.
Table 2. Results of the GLM investigating the relationship between daily count numbers (dependent variable) and weather variables. The
asteriskindicatesthesignicanceoftheweathervariableinthemodel.
Short- toed snake eagle
Bootedeagle
Commonbuzzard
All occurrence
Maximum daily count
All occurrence
Maximum daily count
All occurrence
Maximum daily count
Explanatory Term
Wind direction
Wind speed
Temperature
Humidity
Wind direction
Wind speed
Temperature
Humidity
Wind direction
Wind speed
Temperature
Humidity
Wind direction
Wind speed
Temperature
Humidity
Wind direction
Wind speed
Temperature
Humidity
Wind direction
Wind speed
Temperature
Humidity
Estimate
1.0
-0.1
-0.7
-0.07
1.0
-0.1
-0.7
-0.07
1.2
-0.1
-0.3
-0.04
1.2
-0.1
-0.3
-0.04
1.8
-0.02
-0.9
-0.03
1.8
-0.03
-0.9
-0.03
Z value
1.41
-2.7
-3.0
-1.8
1.4
-2.8
-3.1
-1.8
1.9
-2.5
-1.2
-1.2
1.8
-2.5
-1.1
-1.2
2.4
-0.6
-3.6
-0.8
2.4
-0.6
-3.6
-0.8
P (> |z|)
>0.05
<0.01*
<0.01*
>0.05
>0.05
<0.01*
<0.01*
>0.05
>0.05
<0.05*
>0.05
>0.05
>0.05
<0.05*
>0.05
>0.05
<0.05*
>0.05
<0.01*
>0.05
<0.05*
>0.05
<0.01*
>0.05
S.E.
0.7
0.04
0.2
0.04
0.7
0.04
0.2
0.04
0.7
0.05
0.2
0.04
0.7
0.05
0.2
0.03
0.8
0.04
0.3
0.04
0.8
0.04
0.3
0.03
Table 3. Percentage of adults and juveniles/immatures observed at the site.
Species
Short-toed snake eagle
Bootedeagle
Lesser spotted eagle
Commonbuzzard
Honeybuzzard
Blackkite
Marsh harrier
Adult (%)
4.2
12.5
0
15.1
0
7.1
42
Juveniles/immatures (%)
95.8
87.5
100
84.9
100
92.9
58
Sample size
95
8
6
33
9
28
31
A comparison of two methods for monitoring migrating broad-winged Raptors
17
We would like to thank MEDRAPTORS (www.raptormigration.
org), a network of ornithologists and birdwatchers involved in the
research and the protection of migrating birds of prey through spe-
cicprojectsandobservationcamps.
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Associate Editor: G. Tellini Florenzano
... The proportion of birds showing a reversed direction of migration increases at night (Bruderer & Liechti 1998). In the case of a sea barrier, soaring raptors show reverse migration on coastal areas, flying inland and sometimes flying back from the sea (Agostini et al. , 2000Panuccio et al. 2004Panuccio et al. , 2011Mellone et al. 2013). In this case, among factors affecting reverse migration, wind condition, flock size and time of day are of paramount importance in explaining the flight direction of raptors (Agostini & Duchi 1994;Panuccio & Agostini 2010). ...
... Most juveniles learn this flyway by following adults (see also Mellone et al. 2016), while some, migrating later in the season than older (experienced) birds, head southward passing along southern continental Italy and concentrating over the island of Marettimo (western Sicily; Figure 1) located 130 km NE of the Cap Bon promontory (Tunisia), and rarely also over Malta (Agostini et al. 2002;Sammut & Bonavia 2004;Mellone et al. 2016). Observations made over Marettimo during autumn migration reported tens of juveniles and few immature and adult birds hesitating in front of the open sea, sometimes flying back toward the mainland (Agostini et al. , 2009Panuccio et al. 2011). Such reversed migration has been also recorded in a recent study made by satellite telemetry (Mellone et al. 2016). ...
... In particular, two eagles tracked from their natal sites in southern Italy travelled two and three times between the Sicilian mainland and Marettimo and, finally, spent the winter in Sicily. The proportion of juveniles recorded in southern continental Italy during this research is nearly the same as that reported over Marettimo (between 79 and 95.8%; Agostini et al. 2009;Panuccio et al. 2011). Considering the behavior here reported (as well as at the island of Marettimo), and that at least some birds winter in Sicily (Mascara 1985;Mellone et al. 2016), we suggest that many individuals heading south during autumn movements do not reach Africa, but interrupt their migration or die during the crossing, such as juvenile Egyptian vultures (Neophron percnopterus) attempting the crossing of the Mediterranean Sea between southern Greece and North Africa (Oppel et al. 2015). ...
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We investigated the directions of migration (reversed vs. expected) of raptors approaching a geographical strait in relation to local wind conditions, time of day, flock size and location of the observation post (coastal zone vs. inland zone). Fieldwork was conducted during autumn migration in 2011, 2012 and 2013 at a migratory bottle neck located in the southernmost part of the Italian Peninsula (Calabrian Apennines), using four watch points. In this area, migrating birds face the narrowest water surface between continental Italy and Sicily, the Strait of Messina. The only species showing substantial reverse migration was the short-toed snake eagle (Circaetus gallicus). In particular, eagles, mostly first cy birds, showed this behavior when passing closer to the coast (5 km inland of the Strait of Messina). Our results could reflect the reluctance of these birds to head south when approaching this relatively short stretch of sea, even before reaching the coastline. This behavior could be evidence of the strong selective pressure, which would have led to the evolution of the extremely detoured flight path of birds breeding in Italy.
... At several coastal sites, raptor counts are very uncertain due to their flying behaviour ; therefore, it is usually not possible to determine by eye if raptors really undertake a water-crossing, as shown by our case study at the island of Ustica (Figure 4). Counting migrating raptors at coastal watch sites is likely to produce biased data, and also in this case, the extension of this bias can be very large depending upon different elements, such as the length of the crossing, the time of day, the age of birds, and the morphology of the target species (Kerlinger 1989, Agostini 2005, Agostini & Panuccio 2003, Panuccio & Agostini 2010, Panuccio et al. 2011. In this last study case, the use of radar can determine the behaviour of migrants and the proportion of individuals that do not undertake the sea crossing, as well as identify the variables influencing the water-crossing behaviour. ...
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Capsule: Raptor migration attracts the interest for different reasons, but not all raptor counts achieve the goal of repeatability through the use of standardized field protocols, and this does not allow comparisons of data to be made across years and sites. Aims: We analysed migrating raptor count activities in Italy to verify the interest on this phenomenon by identifying organizers of such counts, and we ascertained the use of a minimum repeatable field protocol (MRFP), and the implications of using it or not. Moreover, we tested the use of radar to support field monitoring. Methods: We analysed 298 migrating raptor counts carried out between 1984 and 2016 by considering characteristics of raptor counts at migratory bottlenecks (number of years covered, use of MRFP, numbers of raptors counted, etc.). In addition, we analysed two case studies using radar to evaluate the effectiveness of raptor counts. Results: There is a growing interest in raptor migration, as well as an increasing use of a MRFP, although differences between counts emerged, probably due to the different aims of the promoting organizations. At sites not using MRFP, more raptors were counted than at other sites, probably because of a greater bias in the data collected. Radar is able to clarify the water-crossing behaviour of raptors at coastal sites, and allows the proportion of birds passing undetected by observers to be evaluated. It also provides data on the spatial density of migrants across a sample area. Conclusions: The use of MRFP is important to harmonize data collection and is necessary to allow comparisons across years and sites. Moreover, the use of radar can be recommended for optimizing raptor monitoring schemes.
... At the Dardanelles Strait, wind speed negatively affected numbers of Common/Steppe buzzards, probably because this species is 2017,[305][306][307][308][309][310][311][312][313][314][315][316][317][318][319][320][321][322][323][324]PANuCCIO, M., DuChI, A., luCIA, g. and AgOSTINI, N. particularly wind selective (Panuccio et al., 2011; Malmiga et al., 2014). here, unlike at the bosphorus, we observed larger numbers of European honey-buzzards both with higher air pressure and higher temperature, ideal weather conditions for thermal activity. ...
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Afro-Palearctic migrants move between breeding and wintering grounds along flyways determined by several factors (bird morphology, geography, behavioural adaptations) and raptors often concentrate at straits to avoid long sea crossings. Here we test the hypothesis that raptor passages across different areas of the Turkish straits are similar in species composition as well as flight behaviour. We made simultaneous observations at the bosphorus and at the Dardanelles in autumn 2010. We tested the influence of weather, time of day and flock size on the intensity and spatial shift of migratory flow as well as the tendency to cross the Dardanelles Strait rather than follow the peninsula. we also collected information of the flight altitude of raptors using an optical range finder. The species composition observed at the two sites was completely different, with eagles predominating at the bosphorus and small and medium-sized raptors predominating at the Dardanelles Strait. Compensation for wind drift at the bosphorus was species-specific, with small and medium-sized raptors showing a drift effect by crosswinds, and eagles showing compensation and overcompensation. Mean flight altitude was similar among species, while the response to weather conditions varied, being mainly affected by wind. In the case of Short-toed Snake-eagles, flight ability and response to weather conditions was also agedependent. These results show that the flight strategies of migrating raptors are species-specific even if some flight parameters may converge as a result of risk minimisation. The differences between species and flyways probably reflect interspecific differences in the ability to fly over water. Key words: bosphorus, Dardanelles Strait, raptor migration, Turkey, weather.
... Also the results obtained from the two birds migrating via the Sicilian route are consistent with field observations that also show a larger number of individuals taking this route. The migratory flow of inexperienced Short-toed Eagles through southern Italy, although less heavy than the one following the western route (Premuda et al. 2015), is quite conspicuous especially on the island of Marettimo, where every October, 150-200 individuals, mainly juveniles (79%; Agostini et al. 2009, Panuccio et al. 2011, are observed, exhibiting the same indecisive behaviour shown by our satellite tracks (Fig. 2b). Therefore, combining both these visual observations and the satellite data presented in this study, it can be argued that every year a small proportion of juvenile Short-toed Eagles (perhaps around 20% of the juveniles raised in the Italian peninsula; Premuda et al. 2015) follow an inherited migration direction, heading to the south without learning the western route from adults, and attempt to cross the Sicily Channel. ...
Article
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Migrating juvenile birds rely on endogenous information in choosing the direction in which to fly, but such input may be over-ridden by social interactions with experienced individuals. We tagged seven juvenile Short-toed Eagles Circaetus gallicus with GPS transmitters in southern Italy. This trans-Saharan migrant flies mainly by soaring and is therefore not well adapted to performing long water crossings. Five of the seven tagged juveniles used the longer but apparently safer route towards the Strait of Gibraltar, while two migrated along a southerly trajectory and subsequently spent the winter in Sicily, apparently forced to do so by the 150-km wide Sicily Channel. One of these individuals took the longer route the following autumn. These results, combined with long-term (15 years) visual field observations involving thousands of individuals, suggest that inexperienced Short-toed Eagles may learn their migratory routes from experienced adults, while some of them migrate south in response to an innate orientation instinct. Transport costs, inherited information and geography apparently interact, forcing some Short-toed Eagles to winter 3000 km to the north of the majority of their conspecifics. This article is protected by copyright. All rights reserved.
... In addition, large numbers of booted eagles, mostly juveniles, reach the Italian peninsula and Sicily to spend the winter. These individuals take the same detoured route performed by short-toed snake eagles (i.e. from Western Europe via north-western Italy), but fly in the opposite direction; only a few individuals are observed attempting to cross the sea between western Sicily (southern Italy) and North Africa (Baghino et al., 2007;Panuccio et al., 2011). The Balkans booted eagles migrate through the Bosphorus, while very few individuals are observed migrating in southern Greece en route to Crete and Lybia (Lucia et al., 2010). ...
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Raptors primarily use soaring-gliding flight which exploits thermals and ridge lifts over land to reduce energetic costs. However during migration, these birds often have to cross water surfaces where thermal currents are weak; during these times, birds mainly use flapping (powered) flight which increases energy consumption and mortality risk. As a result, some species have evolved strategies to reduce the amount of time spent over water by taking extensive detours over land. In this paper, we conducted a meta-analysis of water-crossing tendencies in Afro-Palearctic migrating raptors in relation to their morphology, their flight performance, and their phylogenetic relationships. In particular, we considered the aspect ratio of the wing (calculated as the wingspan squared divided by wing area), the energetic cost of powered flight, and the maximum water crossing length regularly performed by adult birds. Our results suggest that energy consumption during powered flight predominately affects the ability of raptors to fly over water surfaces.
... Along the coast of Thrace 470 individuals were counted in spring 1987 moving toward west and northwest peaking during the second half of March (De Nobel et al. 1990 ) In autumn, at the island of Antikythira a maximum of 105 individuals was reported passing mostly in October (Lucia et al. 2011). Since this species rarely undertakes long water crossings (, Panuccio et al. 2011b), it is likely that individuals migrating through the island of Antikythira spend the winter in Crete, where substantial numbers of common buzzards are regularly observed in winter (Tzortzakaki et al. 2012). On the other hand, observations at DNP and along the coast of Thrace indicate that there is a flyway of this species passing across the Turkish Straits (De Nobel et al. 1990, Schindler et al. 2009). ...
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Greece is located at the southernmost end of the Balkan Peninsula and the shortest distance between Greece and north Africa is roughly 280 km. As raptors mostly fly over land exploiting thermal currents, the ecological barrier shaped by the Mediterranean Sea south of Greece, has a strong impact on the migration strategy adopted by each species. Using data from recent studies at three watchsites in Greece (island of Antikythira, Mount Olympus, National Park of Dadia-Lefkimi-Soufli) we discuss the migratory behaviour of some selected species. The three commonest species were the Eurasian marsh harrier Circus aeruginosus, the western honey buzzard Pernis apivorus and the short-toed snake eagle Circaetus gallicus. The first migrates on a broad front over the sea. A similar migration strategy is adopted also by the Eleonora’s falcon Falco eleonorae. The western honey buzzard performs a loop migration strategy concentrating over the island of Antikythira in autumn but bypassing it in spring. The short-toed snake eagle, on the other hand, avoids the crossing of the Mediterranean Sea performing a long detour and crosses the sea at the Bosphorus. Observations suggest that the levant sparrowhawk Accipiter brevipes and the lesser spotted eagle Aquila pomarina adopt a similar strategy. Finally, species such as the common buzzard Buteo buteo and the sparrowhawk Accipiter nisus do not cross the Mediterranean Sea but move across Greece to winter in southern Greece.
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Capsule: Juvenile Short-toed Snake Eagles Circaetus gallicus hatching in the peripheral populations of Greece and Italy have limited opportunities for social learning of migration routes compared to those hatched elsewhere. Aims: To test the prediction that there would be a higher degree of migration synchrony between adult and juvenile Short-toed Snake Eagles originating from peripheral populations and using an extremely detoured flyway, when compared to other populations using a direct overland flyway. Methods: We use linear regression models to compare seasonal changes in the age distribution of migrating Short-toed Snake Eagles counted at two migration watch-sites in Italy (Arenzano) and Georgia (Batumi), along a detoured and a direct flyway, respectively. Results: Juveniles migrated a fewdays later thanadults at both sites and the age ratios recorded at these two sites was similar. The daily proportion of juveniles increased along a similar slope during the migration season, thus showing a similar degree of synchrony between the age classes on both flyways. Conclusions: Contrary to our hypothesis, juvenile and adult migration is not more synchronized in peripheral populations using a detoured flyway compared to a core population using a direct migration flyway. Our results suggest that juveniles do not learn detours to complete transMediterranean migration from their parents, but from other elders.
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A vast number of raptors migrates between the Western Palearctic and Africa every autumn. Species and/or populations of migratory raptors that choose to cross the Mediterra-nean Sea need to overcome an extended ecological barrier, which is particularly extensive in the area of east–central and east Mediterranean. We tested the selectivity of two raptor species to weather and phenology analyzing the data collected on a small Greek island throughout four different years. Weather selectivity of the two species shows both similarities and differences. The intensity of migration of both studied species is positively correlated with air temperature. The European Honey Buzzard selects days with strong tailwind assistance that helps to reduce flight time over sea thus decreasing mortality risk and energy consumption during this sea crossing. On the other hand, the Western Marsh Harrier seems to be less wind selective reaching the island in good numbers also with headwinds, probably because of its higher ability in using powered-flapping flight.
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Introductory note For the first time in Italy, Avocetta collected the abstracts of some of the Doctoral theses focused on Ornithology and defended in Italian Universities between 2010-2011 and 2014-2015 academic years. The aim of this collection is to offer a review of the research lines on which Italian ornithology is actually working and to offer visibility to researchers who with their doctorates contribute to the development of this scientific field. In this first review, 10 theses were received belonging to six Universities. Overall, the theses spread over six major topics, not mutually exclusive: migration ecology (3), reproductive biology (3), biodiversity and conservation (3), climate change effects (2), evolution (2), sexual selection (1). Five theses are structured as a series of experiments on a unique model species, while the rest consider altogether a set of species sharing common traits. The majority of the theses present results from field-collected data, while in one case results mainly comes from genetic analyses. The most of the chapters of them are already available as published papers, in which case are indicated in the reference list at the end of the review. When the full pdf file of a thesis is available, the appropriate link is indicated at the end of the abstract. Theses are presented in alphabetical order following the name of University and of the doctoral candidate surname. Contents of the abstract are not reviewed and are responsibility of the authors.
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Daily observations were carried out from 23 April to 7 May 2005 over three sites along the Adriatic coast: Mount Conero, Mount San Bartolo (Marche region) and the Po Delta (Emilia-Romagna region), where 1849, 658 and 337 raptors were counted respectively. In addition, two watchpoints in the Mount Conero area were both monitored from 20 April to 20 May 2004, in order to determine the percentage of the migrating raptors starting to cross the Adriatic Sea. Marsh harrier, honey buzzard and red-footed falcon (the latter in Conero and S. Bartolo sites) were the most frequently observed migrating raptors species. The low correlation among the different migration peaks over the three sites seems to show that raptors perform coasting behaviour only partially during spring migration along the part of the Adriatic coast studied. Furthermore, the importance of the Mount Conero as geomorphologic reference sites seems confirmed, since a fraction of the migrating raptors apparently cross the Adriatic Sea towards the Balkans. Nevertheless, further researches are nee-ded at the Mount Conero in order to better quantify the risk of recounting. Riassunto – La migrazione primaverile dei rapaci lungo la costa adriatica (Italia): uno studio comparativo in tre siti. Dal 23 aprile al 7 maggio 2005 sono state effettuate osservazioni giornaliere in tre siti lungo la costa adriatica: Monte Conero, Monte San Bartolo (Marche) e delta del Po (Emilia-Romagna), dove sono stati contati rispettivamente 1849, 658 e 337 rapaci. Inoltre, due punti d'osservazione nell'area del Monte Conero sono stati monitorati dal 20 aprile al 20 maggio 2004, allo scopo di determinare la percentuale di rapaci che cominciano l'attraversamento del mare Adriatico. Il falco di palude, il falco pecchiaiolo e il falco cuculo (quest'ultimo nei siti del Conero e S. Bartolo) sono le specie di rapaci in migrazione maggiormente osservate. Come testimoniato dalle poche correlazioni esistenti tra i differenti picchi di migrazione rilevati nei tre siti, i rapaci mostrano solo parzialmente il comportamento di costeggiare, durante la migrazione primaverile, la zona di litorale adriatico oggetto di studio. Sembra inoltre confermata l'importanza del Monte Conero quale sito di riferimento geomorfologico, perché una parte dei rapaci apparentemente migra attraverso il mare Adriatico verso i Balcani. Tuttavia, altre ricerche sono necessarie nell'area del Monte Conero allo scopo di quantificare meglio il rischio di riconteggio in questo sito.
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Using radar, we studied the migratory flight behaviour of harriers Circus spp. and falcons Falco spp. at the edge of a large water barrier. Arriving at the southern coast of Spain during autumn migration, raptors have to decide whether to cross the Mediterranean Sea by flapping flight (distance at least 150 km) or to fly a detour along the coast of the Iberian Peninsula (250 km) with the possibility of travelling by thermal soaring. In autumn, mean flight directions of falcons (228°) and harriers (229°) were similar, and the majority of falcons (57 %) and harriers (65 %) crossed the sea, preferably with support of following north-westerly winds. A higher proportion of Montagu's harriers Circus pygargus (74 %) than of the larger marsh harriers C. aeruginosus (50 %) crossed the sea. In spring, 65 falcons and 5 harriers approaching the coast from the sea had mean flight directions of 10° and 16°, respectively, and none of them was observed in strong northerly, i.e. opposing winds. In autumn, harriers slightly decreased air-and ground-speed as well as flight altitude when crossing the coast seawards, whereas falcons showed no change in flight behaviour. In spring, falcons approaching the coast from the sea decreased flight altitudes towards land, but no landings were observed within the 8 km range of the radar. The high proportion of birds crossing the sea, even during twilight and at night, and with little change in flight behaviour when crossing the coast seawards in autumn and landwards in spring, indicate that these small raptors are well adapted to cross relatively large water bodies on migration. By selecting following winds and stable weather conditions for sea crossing they reduce flight time to cross the sea and reduce the risks, in particular the potential hazard of sudden weather changes. Keywords: Migration, barrier, sea crossing, Falco, Circus, Mediterranean sea, Spain
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This article presents tests of the theoretical predictions on optimal soaring and gliding flight of large, diurnal migrants using Pennycuick's program 2 for “bird flight performance.” Predictions were compared with 141 observed flight paths of migrating steppe buzzards, Buteo buteo vulpinus. Calculations of cross-country speed relative to the air included bird's airspeeds and sinking rates in interthermal gliding and climbing rates in thermal circling. Steppe buzzards adjusted interthermal gliding airspeed . according to their actual climbing rate in thermal circling. By optimizing their gliding airspeed, the birds maximized their crosscountry performance relative to the air. Despite this general agreement with the model, there was much scatter in the data, for the model neglects horizontal winds and updrafts during the gliding phase. Lower sinking rates due to updrafts during the gliding phases allowed many birds to achieve higher cross-country speeds than predicted. In addition, birds reacted to different wind directions and speeds: in side and opposing winds, the steppe buzzards compensated for wind displacement during soaring and increased their gliding airspeed with decreasing tailwind component Nevenheless, cross-country speed relative to the ground, which is the important measure for a migratory bird, was still higher under following winds. This study shows that Pennycuick's program 2 provides reliable predictions on optimal soaring and gliding behavior using realistic assumptions and constants in the model, but a great deal of variation around the mean is generated by factors not included in the model
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Migratory animals show a suite of adaptations to cope with their journeys. These include not only morphological features for efficient locomotion and storage of energy but also behavioral adjustments to exploit winds and currents or to avoid drift caused by moving fluids. Migration strategies across locomotory modes can be analyzed in the context of optimality models, using some general principles concerning migration range and selection criteria. Comparisons of model predictions with natural behavior help researchers understand the selection pressures that underlie migration strategies. We give examples of typical migration speeds and distances for animals using different locomotion models. Successful migration also requires accurate orientation and/or navigation between distant areas for reproduction and survival. Animals can use a suite of different compasses, which may be cross-calibrated or integrated for direction finding, depending on the geographical and ecological situation, and may be used with an endogenous clock for time compensation.
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Observations were made on the autumn migration of Accipitriformes over the islands of Maret- timo and Pantelleria, located between western Sicily and Tunisia (Central Mediterranean). A total of 7451 raptors was counted between 24 August and 12 September 2003, mostly adult Honey Buzzards Pernis apivorus – 4045, and Black Kites Milvus migrans – 2489. Mixed-age flocks were regularly reported for the Black Kite (1956 adults and 533 juveniles estimated) confirming information transmission concerning orientation behaviour in this species. Al- though in the Honey Buzzard juveniles tend to migrate later than adults, crossing the Mediter- ranean on a broad front mostly after mid-September, we observed some mixed-age flocks, esti- mating the passage of 3830 adults and 215 juveniles. In particular, over Pantelleria we recorded in seven cases juveniles in flocks of adults heading towards WNW, presumably learning (simi- larly to juvenile Black Kites) the shortest route over water to reach Africa from this site. A total of 72 Egyptian Vultures Neophron percnopterus – 62 adults, 6 juveniles and 4 sub-adults – was counted over Marettimo confirming that their greatest concentration during autumn migration through Italy occurs at this island. In this species, all juveniles were seen migrating in flocks of adults. Finally, the passage of hundreds of Marsh Harriers Circus aeruginosus was reported, mostly over Pantelleria. Among adult harriers, it was possible to estimate the passage of birds belonging to different sex classes; unlike in the previous studies made in central, southern con- tinental Italy and Malta during autumn migration, adult females outnumbered adult males (372 vs 298 individuals). Finally, considering the huge number of Accipitriformes observed, Pan- telleria, so as Marettimo, should be enclosed among Important Bird Areas for the autumn mi- gration of raptors in the Mediterranean basin.