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Hellenic Ornithological Society, photo: I.Foufopoulos
Control of populations of seabird competitive species

Drawing: Vassilis HatzirvassanisThe Yellow-legged Gull (Larus michahellis), is the most common and frequently observed gull in Greece. It is an opportunistic species with a breeding range stretching out all over the Mediterranean. During the last decades, the species populations have increased significantly, mainly due to the increase of food sources related to human activities (e.g. rubbish dumps, fishing discards). The unnaturally large Yellow-legged Gull population has a negative impact on other seabird species, triggering problems such as competition for food and nesting sites, or predation of nests. Audouin’s Gull(Larus audouinii), is especially vulnerable as both gull species share nesting and feeding sites.

Yellow-legged gullsIn addition, rubbish dumps will be shutting down in the following years, meaning an important decrease in food sources for the Yellow-legged Gull populations. Although, in the long term, this will probably lead to a decrease in the population numbers, in the short term, it will probably lead to an increase in the pressure on other seabirds this species competes with or predates on. The impact of this process on other seabird species can be avoided, or at least decreased, through the implementation of suitable management measures.

Competition for food: Yellow-legged gulls chasing a Cory’s ShearwaterThe objective of this action is to test different methods of population control for the Yellow-legged Gull at selected project sites, aiming to improve breeding success of other seabird species, such as Audouin’s Gull and Mediterranean Shag. These methods should reduce the species breeding success, which in combination with the shutting down of rubbish dumps will consequently induce a decrease the species population in the area; the latter will have a positive effect on the breeding conditions of other seabirds.

Before any management measure can be implemented, a full assessment of all suitable methodologies and appropriate locations must be carried out, and the population control of the Yellow-legged Gull is no exception. Therefore, existing methodologies already implemented in other regions of the Mediterranean are tested in order to select and execute the most suitable ones. At the same time, HOS carries out an assessment of Yellow-legged Gull colonies in all project sites in order to select those where the population control will be implemented.

Pilot population control of Yellow-legged GullThe assessment of an islet addresses both the number of Yellow-legged gulls and their impact on other seabirds, and the suitableness of the islet for the implementation of the control method. After this, the selected methods will be implemented and their effectiveness monitored, giving special attention to their impact on the Yellow-legged Gull but also on Audouin’s Gull and Mediterranean Shag.

This action will provide the knowledge, know-how and experience on the implementation of population control methods needed to successfully apply this management action in the near future in other areas for the conservation of other seabird species and biodiversity of Greek islands and islets.
 

Results:

Pilot population control of Yellow-legged GullThe assessment of the existing population control methods for the Yellow-legged Gull has evaluated different methods included within the following categories: 1) methods involving the management of Yellow-legged Gull nesting sites, 2) methods involving the control of adult Yellow-legged Gull numbers, and 3) methods involving the control of Yellow-legged Gull breeding success.

This assessment showed that the best methods are those controlling breeding success, such as removal or oiling of eggs.

On the other hand, the assessment of islands and islets involved 144 uninhabited islets with Yellow-legged Gull colonies within the project sites. 13 different parameters were taken into account, including size and location of Yellow-legged Gull, Audouin’s Gull and Mediterranean Shag colonies, total population of each species in each region, distances among colonies, level of predation/competition of the Yellow-legged Gull with other species, presence and management of Yellow-legged Gull food sources (e.g. rubbish dumps, fishing) in the area, etc. Finally, a cost-benefit analysis was applied to determine where the ecological benefits are the greatest, giving as a result a list of high priority colonies where the Yellow-legged Gull population control method should be implemented.

The following table shows the 20 top priority colonies:

Region No. of colonies in each region
Thasos 2
Skyros 6
Limnos 3
Agathonisi 1
Amorgos 1
Arkoi 1
Zakynthos 1
Kinaros 1
North Sporades 1
Kythira 2
Gaudos 1

The first pilot actions for the population control of Yellow-legged Gull were already implemented in spring 2010 on an islet in Thasos, and three islets in Skyros. In total, the action involved 256 Yellow-legged Gull nests, out of which only four eggs hatched. This means the action had a 99% of success. In 2012 a pilot action of Yellow-legged Gull’s breeding performance control continued on islets of Kythera and Thasos which also host colonies of the Audouin’s Gull and Mediterranean Shag. In total 479 nests were treated preventing hatching of 1064 Yellow-legged Gull’s eggs.

Θαλασσοκόρακας & Αιγαιόγλαρος

take part in the Greek seabird population census

 Identify six seabirds at a glance!

Dark coloured, long necked and short tail

Mediterranean Shag: rounded crown, steep forehead, slender bill, thin straight neck.

Dark coloured, long wings, just above the water

Cory’s Shearwater: brown above, white below, long glides.
Mediterranean Shearwater: dark above, light below, quick wingbeats. Usually in flocks.

White coloured gull, with long wings 

Yellow-legged Gull: light-coloured bill, eyes and legs. Dark grey mantle with white edge, and black wing tips, with large white spots. Yellow bill. Most common gull.
Audouin’s Gull: dark-coloured bill, eye and legs. Light grey mantle without obvious white edge and black wing tips, with small white spots. Red bill. Typically observed close to islands and small islets.


Tiny, black, just above the water

Storm-petrel: very small, white rump like a swallow. Very rare

LIFE Natura 2000

LIFE07 NAT/GR/000285
Concrete conservation actions for the Mediterranean Shag and Audouin's Gull in Greece, including the inventory of relevant marine IBAs

The project is implemented by the Hellenic Ornithological Society, in collaboration with the Hellenic Society for the Study and Protection of the Monk Seal (ΜΟm), the Hellenic Centre for Marine Research (HCMR), the Technological Institution (TEI) of Ionian Islands and the Portuguese Society for the Study of Birds (SPEA), with the financial support of the European Commission and the co-financing of the A.G. Leventis Foundation.
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Last update: October 5, 2012

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Hellenic Ornithological Society Hellenic Society for the Study and Protection of the Monk Seal (ΜΟm) Hellenic Centre for Marine Research (HCMR) Technological Institution (TEI) of Ionian Islands Portuguese Society for the Study of Birds (SPEA) A.G. Leventis Foundation
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