Black Storks ride the ridges toward Tarifa in peak passage week

Black Storks are passing over the Sierra de Alpujata.¹ On September 3, watchers at the Mirador de las Águilas above Mijas logged them on half a dozen checklists, never more than two at a time, riding thermals off the ridge on their way southwest.¹ That is right on schedule. September is the peak month for the species at the Strait of Gibraltar, and this lookout, which exists to count soaring birds on the autumn passage, sits roughly a hundred kilometers up the coast from the crossing at Tarifa.

Overhead, a Black Stork (Ciconia nigra) is easy to mistake for its common cousin until the light hits it. Both are the same size, about a meter tall with a wingspan near a meter and a half, and both fly with neck and legs stretched straight out, which is what separates any stork from a heron. The White Stork is white with black flight feathers. The Black Stork is the reverse: black head, neck, back and wings, with a green and purple gloss in good sun, and white confined to the belly and undertail, so the bird reads as dark with a pale patch behind the legs. Where White Storks cross in flocks of dozens or hundreds, Black Storks come singly, in pairs, or in small loose groups, which is why two at a time is a typical count here.¹

The habits are as different as the plumage. White Storks stride through open pasture and follow tractors; Black Storks are shy, wading slowly through shallow rivers and marshes, usually alone, hunting by eye. The bird walks head-down through the water or stands with wings outstretched, then lunges with the long bill. Fish make up most of the diet in the breeding season, with frogs, eels, salamanders, small reptiles and the occasional small mammal filling in. Iberian pairs are unusual among Black Storks in that many nest on cliffs, boulders and overhanging ledges in mountain country rather than in big forest trees, and they are wary enough that finding and monitoring those nests is hard work.²

The birds crossing the Málaga sierras now have a reason to hug the ridges. A stork is a soarer, not a flapper. It climbs on a column of warm air rising off a sun-heated slope, glides to the next, and climbs again. Cold sea makes no thermals, so the last thing a three-kilogram bird wants is to leave land early. The coastal ranges, Alpujata, Sierra Bermeja, then the hills above Tarifa, work as stepping stones that deliver it to the narrowest point of the Strait with height to spare for the fourteen-kilometer jump. Those that cross keep going to the West Sahel, wintering on wetlands in Mali and Nigeria.

Not every Iberian Black Stork makes the trip anymore. Since at least the early 2000s a growing number have stayed to winter in Spain and Portugal, most of them on rice fields, reservoirs and ponds. Spain lists the species as Vulnerable in its national catalogue of threatened species, and the pressures named are the ones that hit its feeding water: altered river flows, drought, over-extraction and pollution, all a long way from a dry ridge like this one.³

Counters at the Mirador de las Águilas have tallied nearly 900 Black Storks since 2008, a small share of the soaring traffic on this flyway but a steady one. A dark stork over the ridge in the first weeks of September is exactly what the lookout was built to catch.