Bird MigrationDynamics of bird migration in SW Portugal

Bird MigrationBirds come, birds go. Millions of them pass through the SW tip of Europe, specially in the post-breeding period. In late Summer and Autumn, the small village of Sagres becomes the birdwatching capital of Portugal. Find out why.

Why Sagres?

Besides it´s resident, breeding and wintering highlights, the most relevant ornithological phenomenon in SW Portugal is most likely to be the post-breeding migration that takes place roughly from August to November. This is particularly visible in Sagres peninsula. The peninsula is like an open window to a massive movement of birds throughout Portugal, which due to its geographical location, concentrates a great diversity and abundance of migrants.

These migrants are mainly raptors and passerines that undertake astonishing journeys, leaving their European breeding grounds on their way to wintering areas south of the Sahara desert, and also dispersing individuals from populations further North.
The coastline and coastal valleys lead the migrants to SW Portugal where they congregate. Which and how many of them arrive, is highly dependent on weather conditions, both in the peninsula and along their journey.

From Sagres, trasaharian migrants can head east along the South coast, presumably to the Strait of Gibraltar, where they can cross to Africa flying over the least area of sea possible. They can also try their luck crossing around 400 km of Atlantic Ocean that lies between both continents, although this a risky path, where many will die. In the open seas, land birds can hardly feed or stop flying, and soaring birds do not have the ascending thermals or hot air pockets that allow them to soar, for they do not form. A lot of the birds that reach Sagres are performing dispersive movements, and head back North, East or NE when they realize the land ends. The waters around SW Portugal are also an important flyway for seabirds travelling in the East Atlantic and in and out of the Mediterranean Sea.

Many of the birds that reach the area are juvenile or immature birds, unexperienced migrants astray from their optimal route through the Strait of Gibraltar. For this reason, Sagres is somewhat of a congregation place for lost birds, where almost anything can happen, and where you have to be alert for the possibility of rare birds showing up.

Meteorological conditions greatly influence the attendance of migrants to the peninsula. Factors like rain, and especially wind direction and speed both in Sagres and further North and NE (and NW for seabirds), condition arrivals and departures, and make each day an unique one. Eastern winds in Southern Iberia per example can blow migrants from Gibraltar, and Southern winds in the Strait can mean that birds that did not make it across, eventually reach the peninsula. However in rainy and windy days in Sagres, bird abundance drops, although diversity remains high. When the weather clears after a few poor days, bird activity peaks, to the birdwatchers delight.

Spring migration can also bring a few surprises to Sagres, but generally speaking it is not regarded as being as overwhelming in terms bird movements of as in the post-breeding period. Birds tend to travel north in a wider front, not being channeled down the coastline and nearby valleys by the dominant North winds that make them congregate in the Autumn. However, Sagres is usually quite unexplored at this time of year, and a good number and variety of migrants do reach the peninsula from March to May, especially when Easterly winds sweep Europe.

Soaring birds

Soaring birds (raptors, storks, herons and some corvids) are the greeting card of Autumn migration in Sagres. Every raptor species that has ever been record in Portugal, was been spotted here in the migration period.
These are mainly juveniles and immature birds that can form flocks, sometimes mixed ones, of dozens or even hundreds of individuals, circulating in the ascending thermal columns. Many of the birds present may was well be performing dispersion movements. One of the particularities of raptor behavior in Sagres is that usually they pass through the area quite low, at least compared to Gibraltar standards.

The most abundant species are Griffon Vulture Gyps fulvus, Booted Eagle Aquila pennata, Short-toed Eagle Circaetus gallicus and Common Buzard Buteo buteo, followed in numbers by Honey Buzzard Pernis apivorus, Black Kite Milvus migrans and Sparrowhawk Accipiter nisus. Birds like Egyptian Vulture Neophron percnopterus, Black Stork Ciconia nigra, Montague´s Harrier Circus pygargus, Hen Harrier Circus cyaneus, Hobby Falco subbuteo and Red Kite Milvus milvus are also frequent visitors. Some less common species like Rüppell’s Vulture Gyps rueppellii, Bonelli’s Eagle Aquila fasciata, Spanish Imperial Eagle Aquila adalberti or Eleonorae’s Falcon Falco eleonorae are also regular although much scarcer. True local rarities like Pallid harrier Circus macrourus or Red-footed Falcon Falco vespertinus have been occasionally sighted in recent years.

These species have different passage timings and peaks. While Griffon Vultures have their peak in October continuing to pass though along November, others like Honey Buzzards have their peaks in September. Black Kites are the earlier birds to arrive (some even in July), with passage peaks already in late August and early September. Booted Eagles pass though by the dozens in the last weeks of September and first half of October, while Short-toed Eagles start to show up in big numbers in October, but continue to be abundant throughout November, time when the Common Buzzard passage is more evident.
No two days are alike here, and between mid-September and early November it is frequent to have days with more than a dozen species of soaring birds in Cabranosa, the local raptor vantage point.

Passerines

Passerine migration is another highlight of the Autumn migration, often neglected or relegated to second plan. Millions of small birds pass through the area heading for tropical Africa, concentrating in shrubs and coastal valleys. By nightfall, an enormous number of silhouettes fly into the dusk in an amazing demonstration of the forces of Nature that move them. The more abundant species present seem to be Willow Warbler Phylloscopus trochilus, Pied Flycatcher Ficedula hypoleuca, Northern Weathear Oenanthe Oenanthe and Yellow Wagtail Motacilla flava, followed in numbers by Spotted Flyctaher Muscicapa striata, Redstart Phoenicurus phoenicurus, Whinchat Saxicola rubetra and Tree Pipit Anthus trivialis. Some days in Sagres, coastal bushes are swarmed with small migrants.
Many other species of migrants use the area as a stopover site before making the big cross or just continuing their journey. Scarcer birds like Boneli’s Warbler Phylloscopus bonelli, Bluethroat Luscinia svecica or Ortolan Bunting Emberiza ortolana are some of the species that can easily go unnoticed. It is always advisable to keep an eye out for rarities, for birds like Red-throated pipit Anthus cervinus, Red-breasted Flycatcher Ficedula parva, or Moussier’s Redstart Phoenicurus moussieri have been spotted.

While these trans-continental migrants pass through mainly in late August, September and early October, later in the season, from October onwards, and especially in the second half of the month and throughout November, the passerine cast changes dramatically in Sagres.
As most transaharian migrants are already in Africa, Northern populations of some common European species arrive in great numbers, fleeing from food scarcity up North, heading south in their search for more abundant feeding grounds, in some cases enlarging already existent resident populations. These are mostly Finches, Thrushes and Corn Buntings. Most common birds of this category are White Wagtail Motacilla alba, Meadow Pipit Anthus pratensis, European Robin Erithacus rubecula, Backcap Sylvia atricapilla, Song thrush Turdus philomelus, Chatfinch Fringilla coelebs, Goldfinch Carduellis carduellis and Corn Bunting Emberiza calandra. Some scarcer wintering visitors include Richard’s Pipit Anthus richardi, Ringed Ouzel Turdus torquatus and Alpine Accentor Prunella collaris.

Seabirds

The waters of the SW are an important flyway for seabird in transit between breeding colonies and wintering grounds, and also juveniles and immature in dispersion. Particularly after rough weather or periods of strong Western winds, pelagic seabirds tend to come closer to shore, offering one of the most spectacular perspectives of the migration phenomenon. Seawatching in Cape S. Vicente in the early mornings can be a rewarding experience.

Northern Gannet Morus bassanus is the most numerous species that cruises by the Cape, especially from mid-October onwards. In some days, rates of passage are in the orders of some hundreds or even a few thousands per hour. Also quite abundant are Cory’s Shearwaters Calonectris diomedea, the endangered Balearic Shearwaters Puffinus mauretanicus, Lesser black-backed Gulls Larus fuscus and Great Skuas Stercorarius skua skua. Regular but somewhat scarcer birds like Sooty shearwater Puffinus griseus, Audouin’s Gull Larus audouinnii, Mediterrannean Gull Larus melanocephalus, Pomarine Skua Stercorarius pomarinus, Arctic Skua Stercorarius parasiticus, Sandwich Tern Sterna sandvicensis and Common Tern Sterna hirundo, are can be spotted from land in due time. Great Shearwater Puffinus gravis and Wilson’s Storm-Petrel Oceanites oceanicus are also quite abundant (especially during the Summer), but require a pelagic trip. Auks like Razorbill Alca torda or the elusive Atlantic Puffin Fratercula arctica are later migrants, crossing especially in November and December. Rarities like Sabine’s Gull Larus sabini and Long-tailed Skua Stercorarius longicaudus have been spotted.

Nocturnal Birds

The migration of nocturnal birds can pass largely unnoticed. However species like Long-eared Owl Asio otus, Short-eared Owls Asio flammeus, European Nightjar Caprimulgus europaeus, Red-necked Nightjar Caprimulgus ruficollis, or even Scops Owl Otus scops occur every year in Sagres, although they are scarce and harder to find as they move in the cover of dusk. A visit to some areas of open country and tree lines after the sunset is the best approach to try to watch them, but never with guaranteed success.

Why Migrating?

Migration is an evolutionary strategy that birds use to maximize the species’ success, driven by food availability. There are many forms of migration. Some of the widest known are altitudinal migration (form higher to lower altitudes), progressive dispersals (where birds just keep moving in search of food), and long-distance travels (where birds undertake one major journey between breeding and wintering grounds). At first impression, this last one apparently defies reasonability, especially for small passerines. So why did birds start performing these marathons?

During the last Ice Age most of the antecessors of today’s European breeders where cornered in Africa, for most of Europe was covered in ice. When the ice started to retreat, bird numbers expanded and consequently food must have turned scarcer, and competition more fierce. In Europe, plant and animal live was growing more abundant and diverse, and there was plenty of food. With cool weather, lots of fresh water and many hours of daylight, insects flourished. That meant good protein supply, plenty of hunting hours and less energy to be spent in feeding. Migration was the answer. It was too much of an opportunity to be missed.

The ones that made it through the journey would have a chance to raise more chicks, and hopefully to be well enough fed for surviving the trip back. So eventually and gradually, birds that performed these long journeys were naturally selected. While migration can prove to be fatal for lots of individual birds, in the big picture is was beneficial for the species. When days start getting shorter and food scarcer up north, this large scale primordial phenomenon starts again, this time with birds heading south to take advantage of the blossoming food supplies in tropical Africa, created by the rainy season that should be finished by then.

So maybe, instead of considering our breeders as European birds that winter in Africa, perhaps a wiser perspective would be to think of them as originally African birds, taking advantage of an European opportunity. Either way you name it, don’t let an ancient large scale natural phenomenon like the post-breeding migration pass you by.

Bird Migration


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