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Wind patterns affect migration flyways and flock size

AVIAN BIOLOGY RESEARCH 9 (3), 2016 159–166

Wind patterns affect migration flyways and flock size of a

soaring bird over sea

Nicolantonio Agostini a,b* , Marco Gustin , Jost von Hardenberg and
c
b
Michele Panuccio a
a MEDRAPTORS (Mediterranean Raptor Migration Network), Viale Partigiani 19, 27100 Pavia, Italy
b LIPU (Lega Italiana Protezione Uccelli), Via Udine 3/A-43122 Parma, Italy
c Istituto di Scienze dell’Atmosfera e del Clima, CNR, Torino, Italy
*E-mail: nicolantonioagostini@gmail.com

ABSTRACT

Water surfaces are natural barriers for raptors mostly using soaring–gliding flight over land during migration.
Among these, the European Honey Buzzard (Pernis apivorus) is a total migrant, breeding in Europe and wintering
in central western Africa. Each spring thousands of buzzards undertake long sea crossings between Tunisia and
southern Italy, concentrating over small islands en route to central eastern Europe. The aim of this research is
to investigate the influence of wind patterns on the flyways used by these raptors during this critical phase of
migration through field observations at four small Mediterranean islands (Pantelleria, Marettimo, Ustica and
Panarea) and at the Straits of Messina between 20 April and 20 May 2006–2013. In our analyses, peak days

were considered for each site. This eight year multisite study allowed the collection of a large data set. While
crossing the Channel of Sicily, migrants concentrated over Pantelleria (southern side of the Channel) during
moderate NW winds, and over Marettimo (northern side) during weaker southerly winds. Over the island of
Ustica (north-western Sicily, Tyrrhenian Sea) raptors were observed mostly with weak southerly winds. Over
the island of Panarea (north-eastern Sicily) and at the Straits of Messina, European Honey Buzzards passed with
weak winds from W and NW, respectively. The average flock size during the peak days was significantly higher
over the island of Pantelleria, where birds migrated during the stronger winds. The results of this study show
that wind patterns affect both migration pathways and flocking behaviour of this species while crossing large
water surfaces.

Keywords: migration, European Honey Buzzards, Pernis apivorus, water crossing, wind, flocking, spring

1. INTRODUCTION et al., 2016). However, crossing water can save both time
and energy when the ratio between the distance around
Birds tend to minimise risks and energetic cost during the barrier and the distance across the barrier increases.
migration by exploiting favourable winds and avoiding Among Accipitriformes, Osprey (Pandion haliaetus),
geographic and topographic barriers, and sometimes harriers (Circus spp.) and kites (Milvus spp.) show
undertaking long detours en route to their breeding and morphology and flight performances which allow them
wintering grounds (Liechti and Bruderer, 1998; Åkesson to undertake long water crossings, while the European
and Hedenström, 2000, 2007; Alerstam, 2001; Agostini Honey Buzzard (Pernis apivorus) has intermediate flight
et al., 2002; Erni et al., 2005; Liechti 2006; Mellone et characteristics between them and Buteo spp., eagles (e.g.
al., 2011a, 2011b; Panuccio et al., 2012; Vansteelant et Aquila spp.) and vultures (e.g. Gyps spp.), which present
al., 2014; Vidal-Mateo et al., 2015). Raptors (especially flight characteristics less suitable for water crossings
the heavier, broader and rounded-winged species) (Kerlinger, 1989; Bildstein et al., 2009; Agostini et al.,
use soaring–gliding flight during their movements by 2015). Thus, although the European Honey Buzzard
exploiting thermals and updraft currents along mountain tends to use soaring–gliding flight over land like Buteo
chains and avoiding crossing large water bodies (Bildstein, spp., eagles and vultures, unlike them it is able to cross
2006; Agostini et al., 2015). Thermals are very weak and large water bodies. Especially during spring movements,
scarce over water, especially in temperate zones, thus thousands of European Honey Buzzards undertake long
birds are forced to use active (flapping) flight during water crossings through the Mediterranean Sea en route
the crossing. Soaring–gliding flight is significantly less between the breeding and wintering grounds located in
expensive from an energetic viewpoint than active flight, Europe and west-central equatorial Africa, respectively.
but it depends on topography and circadian patterns in Conversely, this Mediterranean area is a real ecological
thermal convection (Baudinette and Schmidt-Nielsen, barrier for other soaring raptors such as the Short-toed
1974; Hedenström, 1993; Mellone et al., 2012; Panuccio Snake Eagle (Circaetus gallicus) and the Booted Eagle

www.avianbiologyresearch.co.uk Paper 1500628 doi: 10.3184/175815516X14627928448105