Sibling rivalry

Most of the meadows around here were mown during the recent prolonged dry-spell, but not the ones immediately surrounding our house. During the last week, these have become something of a magnet for the local swifts, swallows, and house martins. Unmown fields harbour more insects than mown ones.

A few days ago, I watched all three of these insectivorous bird species quartering the front field at the same time, flying low above the tall grass. It’s not until you see swifts flying alongside swallows that you appreciate just how much faster they are. Swallows are no slouches, varying their flights between a leisurely coast and gunning along on all cylinders, but the aptly named swifts shot past them with effortless ease: fighter-jets to the swallows’ spitfires.

The following morning, as I worked in the study, I was distracted by a frantic twittering just outside the open window. I recognised it immediately as the sound of recently fledged swallows begging to be fed by their parents. The young birds were perched close to the house on our electrical power-lines. Our walls are two feet thick, and the study window is low and rather small, but I somehow contrived to hang precariously out of the window, craning my neck sideways, to capture a nice shot of an adult swallow feeding one of it young while two of its siblings tried desperately to attract the parent bird’s attention with their pleading open beaks and flapping wings.

When it comes to natural selection, individuals aren’t just pitted against the elements: cold or heat, flood or drought. Nor simply against members of different species: predator versus prey, generalist versus specialist. The struggle is often—perhaps more often—between members of the same species for limited resources: a struggle for mating opportunities, nesting locations, food. This even applies to siblings. When parent swallows return to their fledglings bearing food, the chick that pleads the most energetically is more likely to be the one that ends up being fed. As with the human world, it’s the loud-mouthed extroverts that tend to do best. When it comes to feeding time, it’s every chick for itself. Keeping schtum, not kicking up a fuss is a bad tactic. In times of plenty, every chick might still receive all the food it needs, but in times of scarcity it pays to be outgoing and unreserved.