In 2022 I ran nocmig recording sessions at Earlswood Lakes covering spring and autumn migration. I wanted to see if there was any correlation between recordings I made at this site and the recordings I was making two miles away in my Monkspath garden. I also wanted to get an idea of just how much was being missed at a local patch which is otherwise well watched diurnally i.e. during the day. John Oates’ nocmig record of Spotted Crake on 25 May 2019 had already told us this was happening.

The weather conditions, clear nights with strong easterly and southerly winds, meant that 2022 was not a great year for nocmig. Fewer numbers and fewer species were noted nationally.

The Earlswood recordings were made on a weatherproof SM Mini Acoustic Recorder which cost £400 from nhbs wildlife. Audiomoth would have been a cheaper option. The SM Mini is powered by 4x AA batteries which lasted up to 240 hours. The recordings were made on 64GB SD Cards and reviewed on a laptop using the Audacity app to create sonograms. Results were logged on the Dutch Trektellen website. Trektellen downloads nightly to BirdTrack and becomes available to our County Recorders. Security issues were overcome by screwing the recorder to a wooden pergola in the back garden of an Earlswood birder. My thanks to Joe Owen and Sarah.

It is known that nocmig is more successful over well-lit areas than darker areas where migrant birds are inclined to stay silent. The suburban recording location chosen at Earlswood seemed to offer sufficient artificial light to bring migrants in, whilst being just far enough away from the Lakes not to be overwhelmed by calls of the resident Canada and Greylag Geese, Mallard, Moorhen, and Coot. The calls of Grey Heron, Jackdaw, Robin and Tawny Owls, the other local residents, were less easy to interpret and escape.

An estimated 7314 birds of 52 species were identified in my 1458 hours of recording. The data can be fully interrogated at https://www.trektellen.org/site/totals/3363/2022 but a few headlines can be usefully summarised.

Of the estimated 7314 birds, 5280, or 72%, related to Redwings. The recordings provided the Lakes with our latest spring, 4/5/22, and earliest autumn dates, 20/9/22, for 2022. Whilst the largest Redwing count on any one day was 437 made on 4 November 22. In nocmig terms even for my sites this is unremarkable. I attribute the lower than expected numbers to the weather conditions that prevailed.

Several species, with a pronounced passage, that pass through the West Midlands on migration are less scarce as nocturnal fly-overs than they are as diurnally observed 22 grounded migrants. These include, in some years Common Scoter but not this year, Tree Pipits and Song Thrushes. Song Thrush was the second most recorded passage migrant picked up during my sessions with an estimated 618 birds, or 8% of the total birds recorded. The largest count being 78 on the 4 November 2022. Whether this involves movements of local birds, or continental birds coming here to winter or continental birds passing through en route to France or Iberia is unknown. All I can say is there was no evidence of any Song Thrush migration on this scale diurnally through the Lakes. There are a lot of unknowns when it comes to Song Thrush migration in Britain and a lot of this is surely to do with the fact that it goes on at night and is largely undocumented.

In 2022, an estimated 25 Tree Pipits were recorded at Earlswood nocturnally in August and early September, whilst only one was heard around the Lakes during the day. By way of contrast the mainly diurnal Meadow Pipit was heard and seen frequently during the day around the Lakes but was recorded only once nocturnally.

The first question I had asked myself was if there was any correlation between recordings I made at the Earlswood site and the recordings I was making two miles away in my Monkspath garden.

When it comes to Song Thrush, Redwing and Tree Pipit records these show a good ‘month-wise’ correlation for both of my sites, but I think that this just reflects the passages of Tree Pipits and Thrushes that were occurring nationally. The movement of migrants is influenced by wind direction and velocity, temperature and precipitation in the areas along the migratory route. The wind direction this autumn would have made it unlikely that the same birds were involved at both sites.

When it comes to ad hoc species, I did not record the Wood Sandpiper, nor the Pinkfooted Geese, I recorded at Earlswood here at Monkspath. I did record an August Wood Sandpiper at Monkspath, but on a different date, and I recorded a Quail at Monkspath when there was a passage nationally but I did not record either of these at Earlswood. So when it comes to ad hoc species like these clearly it depends on factors like wind direction and the direction the birds are migrating. The sensitivity of recording equipment used at each location also probably plays a part. But again I was not likely to record the same individual birds flying over both my sites.

Turning to my second question ‘how much was being missed at night’? The Earlswood nocmig recordings have highlighted important passages of Song Thrush and Tree Pipit which would have gone unnoticed otherwise. They have also presented a number of early and late dates for migrants e.g. Redwing. On a number of nights in spring Little Grebe and Water Rail flew around the Lakes uttering NFCs, night flying calls, in territorial/ feeding flights. These were never seen at the Lakes during the day leading to the conclusion that they were locally breeding birds coming in to the Lakes at night from other local ponds.

The nocmig recordings provided the only records for the Lakes for 2022 of the Wood Sandpiper, and the flock of Pink-footed Geese mentioned, and these represented only the fourth records for both of these species for the Lakes.

A number of common waders recorded also passed straight through at night without being seen the previous or following day. These included Whimbrel of which 11 were recorded, and numbers of Common and Little Ringed Plovers, Common and Green Sandpipers, Dunlin, Golden Plover, Oystercatcher and Snipe. Other notable species for Earlswood that slipped through included Flycatchers and Common Gull.

So the answer to my question is yes significant breeding and migration detail is being missed at a site which is otherwise well watched during the day and it would be worthwhile to monitor reserves and local patches nocturnally to supplement diurnal observations. A number of well-known UK bird reserves are already doing this to complete their records of site migration / activity and these records can be viewed on the Trektellen website. The downside for any local initiative is that this does require considerable time and effort. There are various software programmes on the horizon being developed using algorithms to automatically review and identify species on sound recordings but at the moment these are in their early development stage and results appear, like BirdNet, either frighteningly accurate or laughable! But perhaps some targeted monitoring of reserves for what I think are important and under recorded Tree Pipit or Song Thrush passages should be considered.

This screen shot above shows, in a twenty second burst, eight downward strokes of a 24 Song Thrush flocks calls and two tapered smudges of Redwing. So it can be seen it would not be too difficult for anyone to count Song Thrushes.

Some personal nocmig lessons I have learned from the Earlswood Experience:

• That the information I have learned about each species would fill its own paper.

• That important information about resident and migrant species is obtained by recording any night of the year. When we first started nocmig last decade we thought we only needed to record a few narrow monthly corridors to capture what was occurring.

• Rain, strong winds and loud anthropogenic noises may silent resident birds but this doesn’t stop migrant birds.

A sound recorder is best allied to a decent microphone if you want to be able to record and pick up the finer detail of calls. I believe it has led to an under recording of Blackbirds and Pied and Spotted Flycatchers at Earlswood in 2022 when allied to the prevailing weather conditions and distance. But then a poor workman always blames his tools.

John Sirrett