Night owl

This was a thrilling encounter.  I was sitting hoping to see a badger when a tawny owl landed right in front of me, about 5m away.  It was staring intently but facing away from me, presumably hoping to find a mouse or a rat.  The owl sat for ten minutes but then a badger came up behind it.  The owl was increasingly distracted by the badger and kept turning round to watch it. Eventually it gave up and flew off.  It was a memorable experience.

I recorded video to avoid any shutter noise from the camera and found I could get the owl to look towards me by making what I hoped were mouse-like noises.  The photo above is a frame grab from the video.  The owl sat completely motionless for several seconds at a time so I have edited this short extract.  The camera was hand-held but the result is not too bad.

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.

TawnyOwlCam

This all began last week when I found an interesting feather on the lawn (you can see there isn't much grass in the lawn!).

It is a primary flight feather from a tawny owl.  A couple of days later I found another one.  The next night the trail camera was set to look at the foxes and there were two short recordings of what looked like a tawny owl catching worms.

On one of the clips of the dog fox you can also hear an owl in the background.

The following night I set four cameras on the lawn with no result (apart from foxes all over the place) but on the second night one of the cameras recorded this video.  The action is brief so I have added a slow motion replay.

It is interesting that the owl sits so still, presumably because it is listening.  Interesting as well that it looks hard at the camera.  Owls are said not to be able to see infrared light but the camera also clicks occasionally - whether this is something audible from outside, or just a fault on the audio track I don't know.  There was a following clip but the owl was too quick for the reaction time of the camera and all that was recorded was a couple of leaves stirring in the downdraught from the wings after it took off.

Up close with RatCam

I have been experimenting.  One of the limitations of most trail cameras is their inability to focus closer than about 2m. Often the otters are closer to the camera than that and are consequently out of focus.  I had already adapted the Browning cameras I use with a rain hood made from flexible plastic covered with camouflaged gaffer tape.

To allow closer focus I have now also fitted them with high tech close focus lenses, using a lens from +1.25 dioptre reading glasses from the pound shop.  

And it seems to work well.  Although I have managed a few brief otter pictures the main problem so far has been getting the otter into the right place facing the right way as the field of view is necessarily now restricted.  In the meantime I have managed some great rat footage.  These are frame grabs from video.

Rats are not my favourite animals and they are a real nuisance in the reedbeds as they often steal the sardines before the otter(s) turn up.  However, they are intelligent resourceful animals and are part of the great scheme of things.  I have seen them pretty much wherever I have tried to find otters so there are plenty of them about - on a bad night I can end up with 150 rat video clips!  While I am waiting for better otter footage the rats have at least proved that the close focus works.  Not bad for plastic lenses costing 50p each.

This shows how the focus is still pretty good when the rat is fairly close to the camera.

Watch this video right to the end.

I also got a brief glimpse of a tawny owl but unfortunately it was very close to the camera and out of focus.  The reaction time of the camera is said to be around 0.5s and the owl was gone after 2s so it was a very quick strike.

The owl took off very quickly but going frame by frame I can see there is a mouse in its talons.  A pity it wasn't a rat.

I'll keep on experimenting and post better otter pictures if I get some.

Stocktake in the owl box

I regularly hear tawny owls calling in the garden each autumn.  Thinking that it would be good to encourage them, I made an owl box and put it up at the end of 2014, probably a bit late for that season.

I monitored the box with a trail camera in an adjacent tree but there was no activity in spring 2015.  I set up the camera again in autumn that year and on one night did see a tawny owl checking out the box.

It isn't easy to be sure it's an owl from the still photo but towards the end of this video clip it takes its head out of the box and turns towards the camera so you can see what it is.

Despite visiting that one time the owls didn't return.  I presume they already had a nest site somewhere and only visit the garden as it is in their territory.  In spring 2016 there was interest from an American grey squirrel (an invasive alien species) so I had to close up the box for a while.

I put the camera up again last autumn and winter and again this spring but, apart from the occasional great tit standing on the platform, there was no activity.  So after three years I decided to give up and recycle the box into sparrow boxes. I climbed up the ladder this afternoon, planning to remove the box, but as I did so a stock dove flew out.  When I peeped inside I could see a chick.  I took one quick photo with the phone and beat a hasty retreat.  Looking at the photo there is a half size chick and an unhatched egg.

The BTO (British Trust for Ornithology) website says that stock doves nest from March to October and have up to five broods in a year so this is not particularly late.  I expect the unhatched egg is a dud as the chick appears at least half grown.  I'll have to decide now whether to leave the box or take it down this winter.  I doubt that owls will take any further interest in it.  I am happy for stock doves to use it but I don't want to encourage the grey squirrels.

Tawny owl

I took a lot of photos when I went on a bird of prey photo shoot last year and have only so far posted a few of them on this blog.  This tawny owl was unimpressed with being awake in the daytime and kept nodding off, which at least did mean it kept very still.  Here are a few more photos.

Bird of the week - Tawny owl

The tawny owl (Strix aluco) is a fairly common but elusive bird, more often heard than seen.  It has the beautiful dark eyes of a night hunter but uses its supersensitive hearing more than its sharp eyesight.  This photos are of a captive reared bird taken on a photoshoot with Alan Hewitt and Andy Howey.

Tawny owls are woodland birds and are found in most areas of Great Britain apart from the Scottish Highlands and Islands.

Because it is nocturnal the tawny owl is difficult to monitor but the UK population is around 50,000 pairs with year-to-year variations influenced by the availability of prey.

You can see from this EBCC tawny owl distribution map that the UK is part of Europe.

Thomas Bewick gave the tawny owl's other names of Common Brown Ivy Owl or Howlet.  He also wrote "The Tawny Owl and Brown Owl have by the older authors been described as a distinct species; but Latham, Montagu, and Temminck seem to agree in considering them identical, the differences arising merely from age and sex."  Here is Bewick's engraving from A History of British Birds published in 1797.

The commonly used description of the tawny owl's call comes originally from William Shakespeare in Love's Labour Lost, Act V, Scene 2 [Winter]:

Then nightly sings the staring owl, Tu-whit;

Tu-who, a merry note,

You can listen to the female owl's Tu-whit here and the male's Tu-who here.  Listen to Sir David Attenborough's BBC Radio 4 Tweet of the Day on tawny owl here.