The sound of nature

 

 In my continuing efforts to catalogue all the species on my patch, I have splashed out on another piece of surveying equipment. My trail cameras have given me a detailed insight into the mammals using the site — with one obvious exception: bats.

Bats are nocturnal, small and fast, which makes accurate identification difficult. I have seen bats on site and recorded some with my mobile bat detectors, but that depends on me being out in the field every night and staying there long enough to pick up everything. After all, not all bat species fly at the same time of night.

I began by looking at devices sold by Wildlife Acoustics, such as the Song Meter. That got me interested in using sound to identify species. These devices can now help identify bats, small mammals, some insects and birds. Further research led me to the BTO acoustic pipeline, an ambitious programme that analyses sound data and uses machine learning to identify species.

From there, I started exploring the options in earnest, looking at Wildlife Acoustics, Titley and finally Batlogger. After much deliberation over recording types and price, I opted for the Batlogger S2 detector.

The Batlogger S2 is a static logger controlled by an app. The device is small, well-constructed, and easy to use, putting it head and shoulders above the PippyG I had been trying to get to grips with. That said, for the price and with a little perseverance, the PippyG is a good bit of kit — as long as you can understand how to operate it.

The Batlogger app makes setting up the device simple. Strap the unit to a tree with a clear recording area, then activate it using the app. The app works on Android and iOS, connects to the device via Bluetooth, and records its location using the phone’s GPS. You can also schedule when the logger is active. It has an internal SD card, so there is no need to keep swapping cards in and out, and it charges via a lead to your computer, which is also how you download the data.

The data is saved as .wav files, which then need to be analysed. I have used the free version of BatExplorer, but because I am not trained in acoustics or bat identification, I found it difficult to use. It looks like a powerful piece of software, with several ways to present the data, but I needed something a little more approachable.

After experimenting, I opted to use the BTO acoustic pipeline, partly because the analysis is accessible and partly because my data can contribute to wider research, as my bird records on BirdTrack do.

Acoustic analysis is very new to me, but the data produced by the pipeline is clear and approachable. Each automatic identification is given a probability score between 0 and 1. Reading through the literature, the suggested threshold appears to be 0.5, with anything below that disregarded. The statistician in me feels that 0.5 is too low, especially given some of the species suggested in the results. So, for my own analysis, I set two additional thresholds: 0.75 as an amber level, where a species has a good chance of being correct, and 0.9 as a green level, where I felt the identification was acceptable. To help with this, I aggregated the data from the two surveys I ran in June and displayed the results as boxplots. This allowed me to look at the median, mean and interquartile ranges for each record. The final factor I considered was the number of contacts.

So, what species did I find?

After aggregating the data into Chiroptera and other species, for bats at the 0.5 level, 9 species were identified; at the 0.75 level, 8; and at the 0.9 level, 6.

I think it best to use a sensibly high figure as an ID value, so I am only accepting Common Pipistrelle and Soprano Pipistrelle as definitely present on the site, with Brown Long-Eared Bats, Leisler's, and Noctule as possibles. I now plan to review the literature to better understand the ecology of those species at my site. 

The non-bat species, as shown below, offers the most interesting records, but one for which, despite the high probability value, I have the least confidence.

In this analysis, only the Brown Rat fails to reach even the lowest level of acceptance. The other rodent species, like the Wood Mouse and Yellow-necked Mouse, are expected. Wood Mice are widely present on site, and although Yellow-Necked mice have not been identified, they are possible; it's hard to differentiate the two in trail camera footage. 

Harvest Mouse was a very surprising record, and I need to understand their audiology and ecology to determine whether they are likely to be present on the site. There is a section on my patch that is suitable habitat, but it is not in the detector's location.

I know that Bat detectors can detect grasshoppers and crickets, but I would have been sceptical of the presence of two species of Bush-cricket had I not identified a Speckled Bush-cricket nymph only the week before.

Lastly, there are the shrews; they communicate in ultrasound, and so it makes sense they would be detected. Both Common and Pygmy Shrews have been recorded on the site, and Water Shrews are suspected. 

This information gives me some interesting species identifications that warrant closer investigation. I now need to find ways to confirm the presence of Water Shrew and Harvest Mice.

I have only used the logger twice, and I need several more runs and practice with it before I feel more confident. I also really need to understand animal sounds better.

With every new device, my understanding of my patch increases.

A weekend of Wildlife and a salutary tale.

Friday was an exciting day, I saw my first newt. This excitement became grounded as my own hubris was exposed. I was printing off worksheets in the work room when a teacher came in telling me I was needed in the courtyard as another teacher had found a newt. This is not odd, I am often called into deal with sick animals or those in stress. In the past 15 years at the school I have dealt with numerous birds, a rabbit and a hedgehog. I have even been called to check on corpses of Foxes and Grey Herons that have been found on the grounds.

I found the teacher in the car park with a gang of kids huddled round. At their feet was a newt. Carefully I bent and picked it up. It was remarkably lively and crawled gamely across my hands. The kids were fascinated and I took the time for each to take a look and explain why it wasn't a lizard even though it looked like one.

As more cars arrived we cleared the area and I decided to take the newt round to the school garden which had plenty of cover and a pond. I took a quick photo to confirm ID. It was a Smooth Newt but its orange underbelly made me cautious about it being the rarer Great Crested Newt. Nevertheless as I fumbled for my keys to open the gate the newt ran off my hand an plummeted to the tarmac. I quickly scooped it up and went inside. Now the newt was disturbingly still and I feared the worst. I laid it in the water and still it remained motionless. I moved it to a covered side of the pond and still it refused to move. I was terrified I had killed it by allowing it to run off my hand. I decided the best policy was to leave it in a safe place and check on it later.

I left the newt alone for an hour. In that hour the excitement of seeing my first newt had been crushed by the weight of what had happened and I found myself increasingly depressed. the newt had been left in my care and the kids had trusted me to look after it. My colleagues found it mildly amusing but saw the effect it had on me. Eventually I plucked up the courage to return to the garden and check. Barely hoping I opened the gate and found that the Newt had gone. I suspect he was only dazed by the fall and had decided that playing dead was a better option than running. My relief was palpable, I found it a telling lesson in not letting ones own excitement and needs get above those of the wildlife I profess to care so much about.

To continue this blog I thought I would add in some photos from the last couple of days. First of all a shot taken in the glorious sunshine on Saturday.

The next three photos were taken this morning. A second exciting sight was had when myself and my mother spotted a pair of Stoats tussling in the scrub. They were too quick to photograph however.

The first Lady's Smock of the season out in flower on my patch.

Harking back to the last post - A Chiffchaff the sound of spring.

And lastly a close up of the Robin that visits my feeding station.

Evocation

I ve been thinking about this post for a few weeks now and I ve finally got around to posting it.

Quite often when birdwatching it is the call that is diagnostic or reveals the presence of a species. In both cases it is easy to overlook the beauty of a sound or what that sound means, so here are some of my favourite calls and what they mean to me.

The common buzzard wasn't common in England when I was growing up but when I moved to Wales they were everywhere. Returning to Warwickshire in 2000 I found they had now colonised the county. They are majestic birds and their mewing calls are haunting.

Jackdaws are a common species but I love the gregarious nature of their calls, the joy they seem to exhibit in the calls as the wheel around in the sky pulling of some quite remarkable maneuvers.

The call of the Herring Gull is something that reminds me of my few happy years at university by the sea at Aberystwyth. Hearing this call takes me back to watching the gulls on the lawn outside the Llandinam Tower to watching them try and nick chips along the promenade. 

Few bird songs compete with the Skylark and they have a resonance to me because they are with me much of the time in the summer. On a calm day I can hear them from my garden, in spring and summer I always here them as I cycle to work and once at work I hear them on the fields nearby. Sadly major construction around the schools mean that future years will now be silent.

Now you may think having the Grey Heron call as one of my favourites but the sound really does evoke something in me. I used to do Heronry counts and I would hear this sound as the brids flapped over head just glimpsed through the trees. The sound is almost prehistoric and it relates to the manner of this large looming loping shape of a bird so well. Stood amongst the conifers with them calling around me I felt as if I could have been million years ago.

I could go on and on, so many songs have stories or feelings attached to them. I could have included Kingfisher, Kestrel, Tawny Owl and Green Woodpecker but I think these 5 are my top 5.