Thursday, 11 October 2012

Overnight Migration monitoring

I've noticed a few people are trying their hand at monitoring night migration lately. It seems to be popular in the US where software is available to pick out calls. See

So, with nothing to lose, I wrapped my Zoom H2N in a tight plastic bag, put the weathershield on and left it in the front garden overnight! The first problem I encountered was the size of the wav file the following morning. Can't remember how big it was, but it took audacity over half an hour to open it! Fortunately, the Zoom has a built in tool to divide files, and so I chopped the file into 1 hour chunks. These took about 5 minutes to open in Wavesurfer, and once the spectogram was focussed and showing a healthy glow of background noise it was fairly easy to fast forward/scroll through each hour segment.

Lots of unwanted noise at first, but it soon became clear that the vertical signals were fireworks, doors slamming, or twigs snapping. The huge blurred low frequency areas were cars, and yobs falling out of the local pub! I was starting to get a bit disheartened after listening to several dogs barking, and a distant car slam on it's brakes but then out of all the noise, the bird calls started to emerge in the recordings.. Local Tawny Owls came first, and were pretty distinctive after a while. The sonogram long drawn out, and just higher than the man made sounds of the village.

I continued fast forwarding wondering if this was the limit of my kit. You don't get much louder than a family of Tawnies, especially if they are in a tree pretty much above the microphone, but then a high frequency downward sloping call whizzed by. I rewound and played back.. REDWING! Success! This was followed by a handful of Redwings, then a Song Thrush which was even fainter on the tape, but the sonogram was clear as day. So, now I'm thinking, if it can pick up Redwings and Song Thrushes flying over, there probably isn't much that this set up would miss. Any Waders or Wildfowl would definately get picked up, Finches probably would if they went straight overhead.

A sample of results are below, plus the details of how they were obtained.

Overnight Migration monitoring, Hampshire, 6th-7th October 2012:

Redwing 24
Song Thrush 4
Present: Tawny Owl 2

Very faint Redwing:
Redwing Sonogram, Redwing flight call from night monitoring, 6th October 2012, Hampshire

Faint Song Thrush
Song Thrush sonogram, Song Thrush call overhead during night time migration monitoring, 6th October 2012, Hampshire

Very noisy Tawny Owl
Tawny Owl Sonogram, Tawny Owl Sonogram from night monitoring, 6th Oct 2012, Hampshire

Set up details:

Zoom H2N ext

Gain 10 (max)
file type mp3 / 96kbps
auto gain OFF, low cut filter OFF,
Recording mode: MS with very small side lobes

Analyis used Wavesurfer software
Samples extracted and uploaded to Soundcloud taken using Audacity software

Next time, I intend to use auto record, constantly triggering throughout the night. This will generate hundreds of small mp3 files which can be joined together using a single terminal command on the pc merging them into ~60 minute mp3 files for subsequent analysis.