OtterCam in February

Since the mother and cub split up it has been hard to tell which otter is which, or indeed, if there is even more than one. The resident female is probably still here, the dog may still be around or calling in, and the cub could still be hanging around in the territory.  Although the videos are not the best, one of the cameras picked up some intriguing behaviour last week.

On the first night an otter ran up the bank and clearly has a mark on its flank - possibly from an injury.

Four hours later another otter turned up.  It spent a few minutes rolling around on the ground (often slightly out of view so I have edited the footage) and clearly doesn't have a mark so this is a different animal.  I am not sure if just has an itchy back and is conditioning its fur or whether it might also be scent marking.

Much later that night the otter with a mark on its flank ran up the bank again and didn't return the same way.

The next night the unmarked otter returned and was rolling and scratching in exactly the same spot (again I have edited the video) before running up the bank.

And a couple of hours later an otter came down and spent some time sniffing in the same spot.

On the third night an otter came down the bank and spent several minutes rolling and grooming before slipping into the water.

I think this is evidence that there still are at least two otters around and my guess is that the big animal that has been rolling around is the male.  Otters do condition their fur by rolling like this but it could also be a way of marking the territory.

Here is another video from earlier in the month of the otter rubbing itself on the ground and grooming its fur before getting back in the water.

And one brief video left over from when we had the snow.  I had been hoping for a recording of an otter in snow but when it turned up the lens was covered in snow so the picture quality is poor.  Maybe next winter.

The secrets of silent flight

Tawny owls are rarely seen in daytime but are supremely adapted to night-time hunting.  Although they have good night vision they hunt mostly by sound.  They can hear the footsteps of a mouse in the dark and have evolved silent flight so the prey doesn't hear the hunter's approach and so they can still hear it during the attack.

Like most owls, tawnies have large wings which allow slow flight and slow wingbeats but much of the secret of the silent flight is in the feather design.  Last summer I found two moulted tawny owl primary flight feathers in the garden and I recently took a closer look at them.  

They have three special features which are different from other bird feathers.

The leading edge of the feather shows serrations which are tiny comb-like structures that modify the airflow over the wings to reduce noise although the exact mechanism is not known.  The serrations are apparently most well developed on the 10th primary (P10) which directly meets the airstream but are also present on P7-9 (I don't know which feather this is).  Interestingly serrations are much more developed in nocturnal owls (such as the tawny owl) than in diurnal owls.

For comparison here is the leading edge of the owl feather (L) compared with a primary flight feather from a wood pigeon (R).

The upper surface of the owl's feather has a velvet-like covering which is thought to deaden the sound of the feathers moving over each other as well as stabilising airflow to allow slower flight.  The velvet was a bit patchy on this feather but bear in mind it was a discarded moulted feather that had been in use for a year or so.

Here is a comparison of the owl feather and the pigeon feather.

The trailing edge pf the owl's feather is fringed.  The fringes prevent separation of the airflow between adjacent feathers, again reducing turbulence and reducing noise.

Here again is a comparison with a wood pigeon feather.

The amount of fringing varies along the length of the feather although I don't know if that is a function of wear.  This is at the feather tip.

The feather photos were taken with a Canon 100mm macro lens plus stacked Raynox DCR-150 and DCR-250 conversion lenses, giving +12.8 dioptres in addition to the macro lens.

You can read a lot more about the science of owl feathers in a Royal Society publication here.  You can watch a fascinating short video of a pigeon, a peregrine falcon and a barn owl flying in an acoustic laboratory here.

The Herald

I wasn't expecting to write a post about a moth in mid winter so this was a real treat.  This beautiful moth is The Herald (Scoliopteryx libatrix).  It overwinters as an adult, often roosting communally in caves, barns and outbuildings, as here.

These pairs are close together, presumably by chance rather than for warmth.

This one is tucked up with a peacock butterfly.

Herald moths feed up on ivy flowers and ripe blackberries before hibernating.  The caterpillars feed on willow, aspen and poplar leaves in the summer.

The origin of its common name is unclear.  Perhaps because it emerges from hibernation at the end of winter to herald the start of spring or, probably more likely, because its wonderful patterns and colours resemble a herald's tabard.  This is Thomas Hawley, Clarence King of Arms, in 1556.

Look who turned up last night

The foxes come and go so quickly that most nights I don't see who is here.  Last night I was lucky and saw the fox approaching and took a couple of photos to confirm it was the "long-tailed" cub from last year, now full-grown.

Before it had eaten all the meaty bits the fox trotted away but it returned immediately, or so it seemed.  Except that this was the short-tailed cub, which I haven't seen for weeks and assumed had gone.

It is very interesting that both of last year's cubs are still here so late in the season.  I haven't seen either of last year's adults for a while but I guess they are probably still around.  It will be fascinating to see which pair of foxes own this territory this year.  The resident female, whoever she is, is likely to be pregnant by now and her new cubs will be born around the end of March.  With luck they will be in the garden by July.

Last night in the garden

We had a little bit of snow this week, the first of the winter.  I glanced out of the back door window last night just as this fox was approaching so I was able to take a few photos.  I am not completely sure which fox this is - probably one of last year's cubs.  The dog with his torn ear, the vixen with her pale mask and her stocky body shape, and the other cub with half a tail are all very distinctive whereas this fox just looks unremarkable.  I have seen it a few times in the last week or so and it is very wary but hungry enough to approach the house.  Fortunately it can't see me or hear the camera through the door.

Sparrowhawk follow-up

In the rush to add that morning's new photos to Saturday's post I forgot to mention his tail feathers.  Because he was spreading his tail we can see all 12 feathers (rectrices) and it is clear that the second and fifth rectrix on each side is brown whereas the others are grey.  This means this is a second winter bird who has replaced most of his feathers in the first moult last year but has retained a few juvenile feathers.  These will be replaced in the second moult this year.

The same could be seen when he was preening two days earlier although I hadn't really focussed on it then.  You can even see how the juvenile feathers are more worn or frayed, especially at the tips.

The first time I saw this bird as an adult was in August when his new tail feathers were part grown.