Walking along the sea strip I hear above me a rolling whistle of birds calling to each other, which is difficult to locate. The calling gets louder when I recognize a group of bee-eaters a little later (Merops apiaster) in the silhouettes that dance in the thin morning blue. Bees, wasps, dragonflies and butterflies are their prey on this early summer morning.
Bee-eaters are blackbird-sized birds with a butterfly-like flight pattern. They traditionally breed in colonies in Mediterranean regions and hibernate deep in the Horn of Africa. Even today, bee-eaters still hunt above the vast marshes of the Camargue, but they can now also be seen much closer to home. In a warming Europe, these insectivores have expanded their habitat a thousand kilometers northwards in a few decades and have also established themselves in our country as a breeding bird.
Nest tunnel
Back from Africa, bee-eaters dig a horizontal nesting tunnel one to two meters deep in steep walls of sand pits and riverbanks in early May; sufficient to make the temperature and humidity in the adjoining nesting chamber stable and independent of the weather conditions. Here the female lays five eggs in the sand. Three weeks later, in the pitch darkness, the naked blind young hatch from the egg to undergo a metamorphosis in July into eye-catchingly colorful, agile insect hunters.
What is special about the breeding process of bee-eaters is that part of the young is raised not only by the parent birds, but also by other bee-eaters who help the parent pair to incubate and feed – the so-called ‘cooperative breeding‘. The helpers are often male hatchlings from previous breeding years but may also be non-family birds from the colony. ‘cooperative breeding‘ occurs in 8 percent of bird species, but also among mammals such as wolves, for example, where young animals remain loyal to the pack for some time and help raise new cubs.
What is special about the breeding process of bee-eaters is that part of the young is not only raised by the parent birds, but also by other bee-eaters
Evolutionary biologists have long struggled to place the helpers’ altruistic behavior, but explain the emergence of cooperative breeding now based on the idea that both parties – parents and helpers – benefit from this form of cooperation; mutualism.
Helpers increase the chances of successful fledging of young bee-eaters and support the health of the parent birds, while benefiting from the social structure and security of the colony.
Living in colonies with strong family ties, the support of helpers in the breeding process and a high adaptability enable bee-eaters to quickly colonize new territories as Europe’s climate warms. These graceful insect hunters will therefore be seen more and more often in our country.