HUNKERING and BUNKERING

The unseen design elements of bird nests.

((c) Dyfi Osprey project 2013)

Many species of birds build nests which – to our eyes – seem unnecessarily vulnerable to the elements. Herons, most corvids, ospreys and many others choose to make their nests in exposed trees or other high places. Given the vagaries of typical British weather, we worry about them and their broods when the rain falls (as it usually does) and strong winds start to blow. However these nests – or at least the central “egg cup” area of them – could be better protected than you might think. But to understand why this might be, we have to look first at a seemingly unrelated subject: Golf.

All keen golfers will tell you that they love to play on the classic style of seaside course: the “links” - which take their name from the term for an area of sandy, infertile ground between farmland and the sea. Golf courses were first laid out in such places because the land is nutrient-poor and of little use for anything else. Links course are challenging to play on, and test the full skill set of golfers. We rejoice in the wild scenery, the undulating fairways and the tricky sloping greens, and we all agree that seaside courses would be perfect, except for one thing...

Rory McIlroy has a practice bunker

in his back garden at home

Pot bunkers.

We all hate them.

Unlike the wide shallow sand traps found on parkland courses, pot bunkers are small and deep, often with high revetted faces and a cup-shaped bowl of tight-packed sand at the bottom. It is all-too easy to get the ball in one, and difficult – sometimes impossible – to get it out again. Almost every amateur golfer believes that pot bunkers are put there to make the course harder, but that's not the real reason for their existence... 

It's often windy at the seaside, and strong winds would remove the material from a conventional sand hazard in a matter of days, meaning that the grounds staff would be forever having to replace it. The design of pot bunkers means that this doesn't happen: the deeply-shaped recess actually forms a high-pressure area above the sand surface, sheltering it from wind gusts.

Large bird nests have a similar layout to pot bunkers, and the same general aerodynamics. A wide raised rim surrounds a lower bowl-shaped interior, in which the eggs are laid. With this “design”, the weather may be as bad as it likes but the eggs – and later, nestlings – are protected from the worst of the wind, as is the bird which broods them. Rain gets in, of course, but rain itself is not the primary threat to eggs and chicks – as long as there is not too much. It is the WIND, with its effect of carrying away heat, which is the real problem.

So... the next time you watch a poor bird hunkering down in her nest while a howling gale blows around it, don't worry too much. Things may not be quite as bad as they look.