Watching the Dippers today made me realise how fundamental their requirements are. A good habitat of fast flowing, clean clear water that can sustain enough prey for them to find easily and with little effort is fundamental to successful breeding. A female Dipper needs to have built up enough energy reserves to produce a clutch of 4 or 5 eggs with a combined weight of approximately 23 grams, a third of her body weight. For the female who, while the eggs are developing expends a considerable amount of energy on nest building rather than finding food, it is vitally important that she can find prey quickly and in quantity. Nest sites are important. Safety and seclusion are the prime requirements. Being a species that spends it's entire life in or close to the water they utilise the safety of water as a strategy when nesting. Nests are invariably over water or alongside it. I had first hand experience today of how important seclusion is and I am guessing that this is as important as the other two factors already discussed. The pair that I am studying have a large territory, a stretch of river at least 600 metres long and the reason that they have chosen to nest in this particular spot is because it is about as far from human interference as it could be. In my 75 or more hours of watching this spot I have not even once seen another person. This means that they can get on with feeding and building unhindered with the absolute minimum of interference. I arrived at the site way past 11 because of a rainy start to the morning. It was virtually impossible to tuck myself under cover without being seen. After that, as I sat and waited, it was more than 25 minutes before they returned to carry on with nest building. It is not not satisfactory nor acceptable for me to disturb them in this way and I need to find a way to get in to the hide without being seen. Imagine how impossible it would be to successfully breed close to a well used path for example.
Once building had resumed it pretty much went on as before. For example they had finished and departed at roughly the same time as yesterday, around 12.45. The male was the first to start after a little song from the rock opposite. During the session, a Mallard swam up the current and was in front of the nest just inches away. They took real exception to this and perched opposite, both with a beak full, waiting for the duck to move away. The nest is now suddenly taking shape and starting to extend outwards. I can see that it will eventually form a ball that will be closed off gradually, leaving an entrance hole in the front, making it, no doubt even more camouflaged.
I went back to the site after 4 this afternoon and to my utter surprise both birds turned up. They were back at the nest and continuing with building. Not with the same intensity as the morning sessions and it appeared to be the male who was taking the lead. There had been noticeable progress on the nest since this morning so my guess is that they have been working on it through the afternoon. This is a dramatic change in behaviour. It's the first time that I have observed any nest building in the afternoon or early evening.