Tough cases, Dippers

 

I have often wondered, when watching our stream when it is in spate and becomes opaque and fast flowing, how the White-fronted Dippers (Cingle plongeur) manage to find enough food  to eat. I assume that the Kingfishers (Martin-pêcheur) go down to the main river where the waters might be calmer, and they are also capable of local migration to the coast to find better weather, but it is known that many will not survive in very cold weather. 

 

But the dippers seem to stay, I see them nearly every day.

The dippers' diet are aquatic insects; larvae of caddis flies, beetles, mosquitoes, dragon fly, small crustaceans , fish eggs and even very small fish.  Difficult to find in fast, muddy waters. No wonder they have to spend two thirds of the day looking for food!

So I was fascinated the other day to watch a dipper searching right at the edge of the swirling surface and managing to find the tubes of a caddisfly larvae, bringing them up onto the rocks and then repeatedly bashing it hard to break the protective tube to get at the edible beast inside; maybe it did not succeed in breaking the case as it appeared after a while to ingest the whole thing, but it was hard to see. Fish, apparently, are capable of swallowing the entire case.

 

 

Caddisfly cases are rather extraordinary. Soon after the egg hatches the larvae constructs a tubular structure around itself, and then neatly arranged and stuck on to the outer surface of the silken tube. The materials used are grains of sand, larger fragments of rock, bark, sticks, leaves, seeds and shell fragments. The ones I see seem to often have a length of twig along one side, I imagine serving as a sort of external reinforcement to the tube. I took this one out of the water to photograph it.

 

The ones in our stream are made to be portable, with just the front legs and the head sticking out the front. There is another strategy where the larvae constructs a tube attached to the bed of the stream, and being carnivorous, dart out to attack unwary small prey crawling about before retreating into the safety of its case.

 

 

The cases are, of course, the colour of the available detritus that they gather from their habitat, in our case brown and grey. There are reports on the internet of people creating decorative tubes by selecting coloured grains for the larvae to use. They can gather in large numbers in a suitable small pond, and I sometimes watch them slowly crawling about as they graze on organic material. The larvae can turn around in the tube which is open at both ends to allow for water flow and will trim the back end as it grows to avoid it dragging on the stream bed.

So that answered the question of how the dippers were managing to at least get something to eat in the murky waters, but with difficulty. What happened next as I watched goes to show just how resilient and tough these special little birds are.

 

There were, in fact two dippers on the rocks quite near each other. This is of course not unusual, and normally a bonded pair will work side by side. But as I watched clearly these two were not a bonded pair, but rivals and quite prepared to battle it out for this bit of prime stream; I have watched them for nearly ten years and they are always here and successfully breed. The water quality is good, there are two waterfalls which they can hide their nests behind safe even from predators such as mink, who do patrol these waters.

 

 

Suddenly one of the dippers rushed over and grabbed the other, despite the rush of the water.

The battle continued for 20 or 30 seconds before the clutched pair were swept over the waterfall to bob up, apart, in the pond below. Fortunately I had time to get the camera for some hurried shots as they were at it again a couple of minutes later, until one turned and flew in that direct manner that dippers have just over the surface of the water, and pursued by the second, perhaps to continue the struggle further upstream. Males, or females? Impossible to tell, as the sexes are similar.

 

 

 

Dippers swim perfectly well, either on the surface or, having uniquely solid bones that weighs them down, they can walk on the river bed when searching for prey; also a special structure to the feathers that repels water and twice the number of feathers than other similar sized birds, such as robins. Good insulation. These feathers are coated with an oil that they spread over themselves by preening which keeps the feathers in good condition.

 

I have seen blackbirds fighting on roads in the middle of traffic, and sometimes losing their lives as a result. Now I know that dippers are quite capable of taking considerable risks in the desire to control a territory and, within a few weeks from now, raise a family.