Southwest Iberian Mediterranean sclerophyllous and mixed forests

The first cohort of southbound migrants has touched down on the Tagus and Setúbal mudflats this past week—a compressed ecological moment when breeding and departure overlap. Dunlin, Curlew Sandpiper, Common Greenshank, and Ruddy Turnstone are all active along the exposed sediment, while Little Terns remain on their breeding territories on the same shoreline. Mid-July is when the East Atlantic Flyway reaches a biological crossroads: the high-latitude nesting season is not yet finished for some species while the long return migration to West Africa has already begun for others.The earliest arrivals are adult female Curlew Sandpipers, which depart the Arctic breeding grounds within days of laying eggs if conditions turn—often weeks before the males and juveniles that will follow. The estuary itself functions as a crucial fueling station: the tidal flats expose enough invertebrate-rich sediment to let migrants double their body weight before pushing onward. This week, however, water levels have run nearly 30 centimetres above the predicted tide, driven by sustained Atlantic onshore winds—a subtle shift that has forced birds off their preferred low-tide foraging zones and compressed them into narrower strips of exposed mud, intensifying competition during a time when energy reserves matter most.

Orcas have appeared twice off this coast in as many years, each time in July when Atlantic bluefin tuna move north through these waters. The sightings mark an expansion of the Iberian orca subpopulation — a critically small group of fewer than fifty individuals — which has been pushing its range northward from the Strait of Gibraltar since 2020. These encounters are significant: they document a population under pressure seeking new feeding grounds, tracking prey that has sustained it for generations.The tidal range here exceeds six meters, driving productive, dynamic water masses that draw both hunter and hunted. Whether this northward shift represents a permanent range expansion or a seasonal response to changing prey availability remains to be seen, but the pattern is worth monitoring closely.

A Pacific invasive red alga, Rugulopteryx okamurae, has now crossed into the protected waters of Arrábida, marking a decisive new threshold in its year-long advance down the Portuguese coast. First documented inside the park on June 28, the species arrived after moving steadily south from Cascais through Estoril, Paço de Arcos, and Sesimbra—a progression that took less than a year. It smothers the rocky reefs and Neptune grass beds that are the structural backbone of this coast.Summer is peak growing season, and the alga spreads in fragments via dive gear and boat traffic, making even careful recreational use a vector for its expansion. Twenty-two observations across the year show the acceleration of its range, and with established populations now inside a major marine protected area, containment has become far more difficult. What matters now is whether the Mediterranean-adapted reef communities here can adapt faster than this warm-water invader spreads.

The lagoons near Sesimbra hold still water in mid-summer. The reed margins have dried at their tips, the mud at the edges has cracked into pale plates, and the water level has dropped enough to expose a shelf of shallows maybe knee-deep, maybe less. This is where the purple herons are now. Breeding is finished. The birds that spent spring hidden deep in reedbeds, standing motionless in the stems while they incubated eggs, have moved outward into open water. They are visible now in a way they rarely are.The purple heron is a large bird, though it carries itself narrowly. Standing still, it looks almost thin: the neck folded tight against the chest, the body tilted slightly forward, the legs bent at the joint just above the waterline. The plumage is dark. The back and wings run to slate gray, but the neck is a deep rufous-brown streaked with black, and in certain light it reads almost purple, which is where the name comes from. These are threatened birds in the Iberian context, their wetland habitats reduced by drainage and disturbance, which makes the Sesimbra lagoons genuinely important ground. When a purple heron stands in the shallows here, it is not a casual visitor. It is using one of the few places along this coast where the conditions still work.The hunting posture is one of the more deliberate things you can watch a bird do. The heron moves in increments: one foot lifted and placed without a ripple, the body held low over the water, the neck beginning to extend. It can hold that extension for a long time, the bill angled down at the surface, before anything happens. When it strikes, the movement is a single fast contraction of the neck, the bill entering the water and closing. What it is after in these lagoons is primarily fish. Common two-banded seabream move through the shallows here, young fish using the warm marginal water as feeding and refuge habitat. They are not large, typically a few centimeters in the juvenile and sub-adult sizes that frequent the shallows, and the heron takes them from just below the surface. The seabream are themselves threatened along this coast, pressured by overfishing in the wider marine environment, so both species are operating with reduced numbers relative to what this coastline once held.The heron also takes frogs, large invertebrates, and occasionally small mammals when hunting along the marsh edge. In mid-summer the shallows warm quickly, and the fish tend to be most active in the early morning and again in the evening, which is when the herons hunt most intensively. During the heat of the day the birds often stand in shade at the reed margin, waiting. The black-crowned night heron, which also uses these lagoons, shifts its hunting into darkness entirely, which means the two species partition the same water across different hours. The night heron is stockier, shorter-necked, and takes smaller prey on average. The purple heron works the deeper edge of the shallows where its longer legs give it access to water the night heron cannot easily stand in.Post-breeding dispersal in mid-summer means the birds are less territorial than they were in spring. Young birds from this year's nests, now independent, are moving through the region, testing habitats. Some will push south into Africa before autumn. Others will remain on the Iberian wetlands through the season. The Sesimbra lagoons, sitting between the limestone hills and the coast, collect water from the surrounding catchment and hold it into the dry season, which is why they continue to function as hunting ground when other wetlands have dried entirely.If you are near the water now, look along the reed margin where the stems thin out and the open shallows begin. The heron, if it is there, will not move much. You may see it as a dark vertical shape before you recognize it as a bird. The cicadas are loud in the scrub above the lagoon. The water at the heron's feet is barely moving.