Enjoy the migration in Andalusia
Millions of birds cross the Mediterranean twice a year to transit between their European breeding grounds and their African wintering quarters… They are not alone, accompanied by immense quantities of migratory insects which often go unnoticed.
Migration of vertebrates
When one thinks of the phenomenon of migrations on the European continent, flocks of storks immediately come to mind… Only a minority of bird species are resident in a given territory all year round, all the others making seasonal long-distance movements. These migrations are mainly motivated by the lack of food during the winter in high latitudes and are distinguished from simple dispersal in that they involve a route traveled twice a year. The same individual makes a trip from south to north at the end of winter to initiate reproduction, and another trip from north to south when it finalizes.
In some high places for observation, birds gather there in large numbers before passing an obstacle. Europe’s most famous “bottleneck” is none other than the Strait of Gibraltar, where millions of birds “jump” between Europe and Africa. Let’s not forget the movements of marine fauna (seabirds, cetaceans, fish), which are more difficult to study by nature observers, who also cross the strait between the Mediterranean and the Atlantic.
Finally, let us mention mammals, and in particular bats, which migrate between breeding and hibernation colonies, short and regional movements for most species or even on a continental scale for a few species such as the common noctule (Nyctalus noctula). Among terrestrial mammals, ungulates exhibit short-distance seasonal movements in Andalusian mountainous areas, even though today they are most often cut off by hunting fences.
Raptors and storks in the Strait of Gibraltar
Storks and raptors are large species, with diurnal activity and gliding flight (i.e. with few wing beats), taking advantage of the ascending thermal winds formed solely by convection of solar radiation absorbed by the ground. The migratory routes of these birds minimize the transit at sea, where these thermal lifts do not form, forcing a type of flapping flight.
The Strait of Gibraltar is one of the most important crossing points between the northern and southern hemispheres, crossed by between 300,000 and 500,000 soaring birds from Western Europe: one-third storks and two-thirds large raptors. The pre-nuptial spring stage is longer (February-June), with fewer individuals (only mature individuals), while the post-nuptial autumn stage is enriched with youngs of the year and is generally more concentrated (August-September). The months of June and November to February are the quietest in terms of migration. The autumn migration impresses above all with its large groups, especially if bad weather blocks them for several days on the European side. However, the prenuptial migration offers the moving spectacle of birds arriving in Europe, exhausted and flying at very low altitude, and is generally denser during the month of March.
The species follow an established order of passage, of which the Honey Buzzard (Pernis apivorus) is an excellent marker with its very short and abundant migration (100,000 specimens): it is the last species to migrate north (pre-nuptial) and almost the first to finalize the post-nuptial. As for the migration of white storks (Ciconia ciconia), it becomes complex to the point of bringing together at the end of summer groups in post-nuptial migration (Northern European storks descending in summer according to the classic pattern), groups already returning -very early- from Africa (southern storks which were the first to descend) with storks which no longer cross the strait towards Africa.
Short toed eagle
Soraing birds seasonality in the Strait of Gibraltar
Massive migration of 30 to 50 million birds per year, but this phenomenon goes largely unnoticed because it occurs mainly at night. More info later 😉
Sea birds in Andalusia
At least some sea and coastal birds migration is visible every day of the year in the Strait of Gibraltar with about 35 species passing through. In winter, once the breeding season is over, sea birds are attracted by the high productivity of the Alborran Sea, an internationaly important area for those populations.
– Cory’s Shearwater (Calonectris diomedea) > 600,000 birds.
– Gannet (Morus bassanus) >100,000.
– Razorbill (Alca torda) >30,000.
– Balearic shearwater (Puffinus mauretanicus) >23,000. 100% of the world’s population passes through the Strait.
Best spots on the Strait of Gibraltar: Punta Carnero and Tarifa. Other spots of major interest in Andalusia: Coastline of Doñana, Lighthouse of Chipiona (Cádiz), Calaburras (Málaga), Cabo de Gata (Almería). Reference of one year survey.
Migratory marine fauna in the waters of the Strait
Although more discreet and difficult to observe with binoculars, we cannot forget the marine fauna which transits between the Mediterranean Sea and the Atlantic Ocean, and whose ideal observation point is obviously the Strait of Gibraltar. On the contrary, most animal species drift and transported by ocean currents (plankton). Censusing marine fauna is an extremely complex task, and for this reason the following figures are given in order of magnitude, always taking into account significant variability.
Among the seven common and easiest cetaceans to observe in the Strait, two are long-distance migrants and the most imposing ones: Sperm whales (Physeter macrocephalus = P. catodon) with more than a hundred sightings per year and fin whales (Balaenoptera physalus) with less than a hundred observations per year.
There is very little quantified information on loggerhead sea turtles (Caretta caretta). Unfortunately they have disappeared as a regular breeder on the Andalusian coast.
Loggerhead sea turtle
Loggerhead sea turtle
Among the fish, let us mention the Bluefin Tuna (Thunnus thynnus), known and fished since Antiquity, which spends the winter in the cold waters of the North Atlantic and returns at the end of spring to the warm waters of the Mediterranean to reproduce, after a migration of more than 2,500 nautical miles (> 4,500 km), forming schools of several thousand individuals. Favorite prey of the Straits’ killer whales. Less than 10,000 bluefin tuna are caught each year in the traps (“almadrabas”). Swordfish (Xiphias gladius), eels (Anguila anguila) and many other commercial species are also migratory. Although very mobile, it would seem that the Atlantic and Mediterranean populations of swordfish do not cross the Strait (even if they feed there) and do not mix.
Migration of insects
In invertebrates, body temperature varies directly with the environment. The winter cold, typical of the temperate climate, supposes a severe limitation due to the freezing of the tissues and the absence of food resources. In general, insects survive the winter by entering a temporary dormant phase (diapause) until the following spring. These species carrying out their complete life cycle in a territory are considered resident.
Other insects not resistant to winter inclemencies are nevertheless able to colonize a region from southern latitudes thanks to the dispersal capacity of winged adults. These south-north movements are easily detectable on a continental scale when conditions are favorable for population explosions of high-flying insects. When, in addition, the existence of a North-South autumnal flight is verified, then the species is considered as a long-distance migrant (strict definition). Unlike vertebrates, the same individual does not perform both journeys and the cycle is completed by several generations (multigenerational migration).
A great intra- and inter-specific plasticity determines a great variability of situations between years and latitudes… The Red admiral (Vanessa atalanta) returns to the Mediterranean in autumn when its host plant (nettles) is again available there produces a winter generation, however this butterfly can also go into diapause and survive to adulthood in northern Europe. Another spectacular example, the Monarch (Danus plexippus) is a long-distance intergenerational migrant in North America, but behaves as a resident in southern Europe, where its range is limited by frost-free environmental conditions because this population does not go into diapause.
Insect migrations are often difficult to observe and knowledge of them has grown enormously in recent decades.
Migratory butterflies in Spain
Entomologists discovered only a few years ago that the Painted Lady (Vanessa cardui) is the longest known migrant butterfly in the world, making an annual trip between West Africa (Senegal) and northenr Europe (Scandinavia), and can cover up to a distance of 14,000 km in 6 generations. The Red admiral (Vanessa atalanta) is another migrant whose southward journey focuses on the Mediterranean. Other species very common and resident in Andalusia also migrate to northern Europe, such as the Clouded yelow (Colias crocea), Small white (Pieris rapae), Cabbage white (Pieris brassicae) and Lang’s short-tailed blue (Leptotes pirithous). Some species, rarer in the south of the Iberian Peninsula, seem to migrate locally, such as the Queen of Spain fritillary (Issoria lathonia). In some cases, the Mediterranean constitutes the northern limit of invasion of North African species such as the Desert orange tip (Colotis evagore) and the African monarch (Danaus chrysippus).
Lang’s short-tailed blue
Queen of Spain fritillary
Piéride du câprier
Migratory moths in the Iberian Peninsula
Moths, 90% of Lepidoptera, host the largest number of migrating insects. The most powerful sailfish are found in the Sphingidae family: the Hummingbird hawkmoth (Macroglossum stellatarum), an unusual species and very easy to observe thanks to its diurnal habits. Other migrants are visible in Andalusia: adults attracted by artificial lights and caterpillars, with remarkable colors, feeding on their host plant. These include the Striped hawkmoth (Hyles livornica), Convolvulus hawkmoth (Agrius convolvuli), African death’s-head hawkmoth (Acherontia atropos), Oleander hawkmoth (Daphnis nerii) and Vine hawkmoth (Hippotion celerio), the latter very rare in the rest of Europe. The huge Noctuidae family also hosts many migrants, the most abundant of which feed on various host plants (polyphagous) and often have a devastating impact on agricultural crops, as in the case of the Mediterranean brocade (Spodoptera littoralis) or the Silver-Y moth (Autographa gamma), the latter easy to observe due to its diurnal habits. There are many other remarkable species such as the Crimson-speckled footman (Utetheisa pulchella) or the Diamondback moth (Plutella xylostella). Indeed, dozens of species breed in the Mediterranean and Africa and disperse to northern Europe during the summer when conditions are no longer unfavorable there.
Migratory dragonflies in the Mediterranean basin
It is easy to see in the field the great flight capacity of dragonflies. Newly emerged adults disperse to distant areas and reach sexual maturity there before recolonizing a favorable aquatic area. A small number of species perform bidirectional migratory movements and in large numbers of individuals, usually dragonflies breeding in temporary Mediterranean or Sahelian wetlands. Doñana is the largest European reserve for these migrants, whose larvae can withstand a certain salinity. This is the case of the Vagrant emperor (Anax ephippiger): a small number of adults colonize Doñana at the end of winter from Africa; the next generation is more or less numerous depending on local conditions and the most favorable years experience population explosions in Doñana or other Sahelian wetlands; the species then invades the rest of the continent, being able to produce a third generation of adults in the high latitudes. It is unclear whether this generation is making a return trip south. This southern migration has been observed in the Migrant hawker (Aeshna mixta) which disperses from Doñana (before its summer or spring drying up) towards the arid mountains of south-eastern Spain and colonizes large parts of Western Europe. Third species: Huge groups of Red-veined darter (Sympetrum fonscolombii) are sometimes seen in late spring, mainly moving along the coast from Doñana or another Sahelian wetland. Finally, let’s mention Sympetrum sinaiticum, an odonate typical of the streams of the Spanish Mediterranean arc, which aestivates in the mountains before recolonizing them in autumn.
Locust swarms in southern Europe
While most grasshoppers (order Orthoptera – suborder Caelifera) are sedentary, a few species group together in swarms that can reach millions of individuals which move on a continental scale following a main direction without any return movement and are therefore not not considered as migratory species in the strict sense. However, it could be argued that these movements are part of a long-term survival strategy… Initially, as the herbaceous vegetation dries out, the densities of locusts (in the solitary phase) increase as well as direct contact between individuals, which trigger a hormonal reaction. The following generations gradually change in appearance, acquiring a shape with more elongated wings and a more robust and dark body by pigmentation melanin pigments (migratory phase). Then the swarm begins to move over long distances in search of areas richer in food… This phenomenon occurs especially in regions of Africa, with swarms of Desert Locusts (Schistocerca gregaria) reaching the Canary Islands. A few isolated individuals have been found in Andalusia. Although less well known in Europe, invasions of locusts (“langostas”) were not uncommon in the 20th century in the Iberian Peninsula: Moroccan locust (Dociostaurus maroccanus) and Short-horned grasshopper (Calliptamus barbarus). We can also mention the Migratory Locust (Locusta migratoria), a resident species (without a migratory phase) nowadays in Western Europe and probably originating from the Asian plains.
Migratory flies in Andalusia
Among the diptera / flies (insects characterized schematically by having two wings), the Hoverfly family (Syrphidae) stands out, insects very similar to wasps in their yellow and black colors. Some of these hoverflies are highly migratory and regularly visit gardens and patios in search of food (nectar for the adults, aphids for the larvae). The Marmalade hoverfly (Episyrphus balteatus), Migrant hoverfly (Eupeodes corollae) and Long hoverfly (Sphaerophoria scripta) have a very marked peak in abundance in spring and more discreet in autumn. These species, of mainly European distribution, migrate in autumn towards the south, and in winter in the hot Mediterranean zones (Iberian peninsula, Maghreb). Many other hoverfly species are also migratory.