by Connor Panter
Many species of European birds of prey (otherwise known as raptors) journey along migratory flyways in the autumn to wintering grounds in Africa. Throughout the spring these birds migrate back to Europe to breed during the summer months. Raptors act as valuable indicators of ecosystem health because they are ‘apex predators’, occupying the upper trophic levels of most terrestrial European ecosystems. As well as this they are easy to monitor in comparison to more cryptic species of avifauna and are sensitive to changes in environmental and climatic conditions (Kovács et al., 2008).
Raptors can be separated into two groups depending on their flying technique. Those that fly by constantly flapping their wings are recognised as ‘active flyers’ and include falcons, harriers and sparrow hawks, these species typically move along a broad front and can undertake long sea-crossings (Agostini et al., 2017). Species that rely on thermal air currents to glide and soar through the air with minimal energy expenditure are known as ‘soarers’ and include buzzards, eagles and vultures. The temperate biome that extends across much of the European continent provides little thermal activity over water bodies, which along with the topographical constraints formed by mountain ranges results in the formation of migratory ‘bottlenecks’; often over short stretches of water and along narrow land bridges. These bottlenecks include the Strait of Messina between Italy and Sicily, the Strait of Gibraltar in Spain and Batumi in Georgia (Middle East).
The Strait of Messina is the most important bottleneck along the Central Mediterranean flyway (Panuccio et al., 2016) as birds travelling along this route in the spring are typically returning to their breeding grounds in central and northern Europe. Since the 1990’s research conducted by the Mediterranean Raptor Migration Network (MEDRAPTORS) and the University of Pavia has focussed on the behavioural ecology of migratory birds and the effect of weather on flock size and flow across the strait. These measures are important to assess current European population sizes and for future projections.
Species observed during the 2018 spring counting season
Between March and May this year over 21,000 migratory birds were recorded passing over the Strait of Messina study site. The European Honey Buzzard (Pernis apivorus) was the most numerous species recorded and amounted to approximately 80% of all observations. Birdlife International estimated the number of European breeding pairs to be between 118,000-171,000 in 2015 and as such the strait of Messina is a critical flyway for a large proportion of the Honey Buzzard population. A total of 1,382 raptors passed over in a single day during the spring counting season and included frequent migrants such as European Honey Buzzards (Pernis apivorus), Marsh Harriers (Circus aeruginosus), Montagu’s Harriers (Circus pygargus) and Black Kites (Milvus migrans). Excluding P. apivorus, these species represent 9% of the observations recorded during the 2018 spring season. Rarities such as the endangered Egyptian Vulture (Neophron percnopterus), Golden Eagle (Aquila chrysaetos) and the Eastern Imperial Eagle (Aquila heliaca) have also been recorded at the study site in the most recent count season (Straitobservatory.com, 2018).
Soaring raptors frequently gather in large flocks in close proximity to thermal updrafts and perform tight circling movements along the flyways; this is termed ‘kettling’ by ornithologists. Kettles comprising of 20 birds or less were commonly observed over the Strait but kettles consisting of over 100 birds were also recorded during the count season. Birds are usually counted by visual observations as they ‘stream’ away from a kettle and pass a designated point in the landscape (e.g. a structure such as a pylon). Visual observations are the most widespread method for monitoring migrating birds across the world, however, this manual observation approach can be limited by factors such as distance, weather conditions, time of day and topography (Panuccio et al., 2015). Thermal activity peaks around midday when birds take advantage of the favourable soaring conditions and tend to fly at high altitudes. Therefore, visual observations are often less frequent as birds pass undetected; this is known as the ‘midday lull’ (Panuccio et al., 2015).
Marine Surveillance Radar (MSR) is also currently being used to monitor birds passing over the Strait of Messina. Horizontal and vertical MSR is used in conjunction with Geographic Information System (GIS) software and enables researchers to calculate interspecific differences in ground-speeds along with flight altitudes. MSR also allows large flocks of birds to be counted that would otherwise have gone undetected by visual observation. Optimum data capture is achieved when both visual observations and MSR techniques are combined (Panuccio et al., 2015). This methodology allows flight metric data to be collected at the same time as species name data.
Threats facing migratory raptors
The greatest threat to the majority of raptor species currently is habitat degradation (specifically the loss of breeding, staging and wintering sites) along with changes to the climate (Barca et al., 2016). Furthermore, illegal hunting has been entrenched in several cultures for many years. Despite this the number of hunters in rural Italy have decreased by 50% since the 1980’s and hunters now represent 1-2% of the population (ISTAT, 2007). Even though hunting has decreased dramatically within Italian culture, it still remains a widespread threat to migratory raptor species across Europe and the rest of the world. Collisions with anthropogenic structures and trapping of raptors are other substantial threats facing birds of prey along their migratory flyways (Cianchetti-Benedetti et al., 2016).
In addition to this a study published in 2008 by de Lucas et al. revealed that the Griffon Vulture (Gyps fulvus) accounted for the highest number of collision mortalities from wind turbines in Southern Spain. The study site was located close to the Strait of Gibraltar bottleneck; however this study indicated that wind turbines do not have a detrimental effect on the species’ population overall in Spain. Despite this, the authors still suggest that additional studies are required to assess the long term impact of wind turbines on migratory bird populations for future conservation planning. Birdlife International reported that approximately 100,000 raptors are illegally killed in the Mediterranean every year and lists Reggio Calabria province as one of Italy’s worst locations reported for the illegal killings of birds (Birdlife International, 2016).
What are the main drivers for these killings?
The key motive for the illegal killing of birds is hunting for sport where raptors become abundant targets in migration bottlenecks. It has been noted that raptors are sometimes seen as a hindrance for wind farms and that permission may not be granted in areas where raptors are present (DW.com, 2017).
It has also been reported that taxidermy has also had a minor impact on global raptor populations. However, in Spain this practice poses a notable threat to rare species (DW.com, 2017).
An additional study conducted by Cianchetti-Benedetti et al. in Rome suggests that raptors are under increasing threat of illegal shooting within Italy’s urban environments as well as rural landscapes.
In Georgia, local communities still undertake the traditional practice of raptor trapping. This process typically targets the Eurasian Sparrow Hawk (Accipiter nisus; Van Maanen et al., 2001) which then enter the falconry trade or are used to hunt for quails (Coturnix coturnix). Goshawks (Accipiter gentilis) are also targeted by traditional trappers and are used to hunt larger game species such as rabbits (Batumiraptorcount.org, 2018).
What does the future look like for migratory raptors?
Migration is a hazardous process and exposes migratory birds to a myriad of threats, many derived from human activity. Birds flying lengthy distances cross numerous political borders between countries with differing environmental policies, legislation and levels of conservation protection. It is of paramount importance that international relationships between governments, NGOs and stakeholders along the migratory flyways are maintained to enable the sharing of information and conservation efforts to protect migratory birds. Multilateral environmental agreements such as the Convention on Migratory Species (CMS) provides the legal framework and coordination necessary to protect birds along their migratory route, but more work needs to be done with small rural communities and the resourcing of poor countries to mitigate the impacts of illegal hunting during the migration season (Worldmigratorybirdday.org, 2018). Finally, advances in technology used in ecological research such as GPS telemetry, RADAR and in observational equipment (such as spotting scopes and binoculars) will continue to reveal new information about migratory bird behaviour, ecology and population trends.
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Barca, Lindon and Root-Bernstein (2016). Environmentalism in the crosshairs: Perspectives on migratory bird hunting and poaching conflicts in Italy. Global Ecology and Conservation, [online] 6, pp.189-207. Available at: https://www.sciencedirect.com/science/article/pii/S2351989415300482#f000010 [Accessed 23 May 2018].
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Author biography: Connor is studying BSc Ecology at the University of Brighton in the UK. At present, he is completing a one-year research placement at the Royal Botanic Gardens Kew. Connor has interests in the large-scale conservation of flora and fauna, GPS telemetry, biogeography and conservation assessments. He is willing to discuss anything ecological! Follow him @ConnorEcology or contact firstname.lastname@example.org