During my years of fieldwork on Scottish ospreys, I had recognised that some parents were always successful and often reared broods of three young, while other pairs usually lost some of their young and finished off with either one or two chicks, or even none. I put this down to the fishing skills of the males – some are excellent fishermen and others are poor at catching enough fish for their family – while in local hierarchies the dominant males always have first choice at fishing locations. In consequence, some nests might hold three big young while others had young of different sizes, due to food shortage, and it was not unusual to find runts. This was exacerbated in long periods of heavy rain, when fishing was difficult and even whole broods would die. In the wild there were clear differences in the ability of adults to rear strong young.
Restoring the Wild
Roy Dennis