Timed Tetrads and Roving Records

Last year’s Axe Estuary and Seaton Bay Bird Report included an article by Gavin Haig on his enthusiasm for sea-watching. One of my enthusiasms involves attempting to count common birds, often in ‘ordinary’ countryside, as part of national surveys organised by the British Trust for Ornithology. These surveys have led to Atlases of Breeding Birds (1976), Wintering Birds (1986), and the New Atlas of Breeding Birds (1993). The latest survey, using both timed tetrad visits and roving recorders, started in November 2007 and is scheduled to run for four years, until summer 2011. 

Tetrads (2 km x 2 km squares on Ordnance Survey maps – see my article in AVDCS Newsletter no. 64) are visited for four hours in winter and for four hours in summer, with all birds seen or heard recorded. These are ‘Timed Tetrad Visits’, which should give some idea not only of which species are present, but also an estimate of their relative abundance. ‘Roving Records’ of additional species, on the other hand, can be added for any area by anyone, but give only an indication of presence of a species at some time during the year. Of some 100,000 tetrads in Britain and Ireland, 5 fall entirely within 5 km of Axmouth Bridge, 10 are partly within that area, and 4 are partly sea. (The area within 5 km of Axmouth Bridge is that covered by the Axe Estuary and Seaton Bay Bird Report).

My involvement with the Undercliffs National Nature Reserve led me to start in the coastal tetrads east of Axmouth. In the fields above the Undercliffs, the flocks of Linnets, Skylarks and Yellowhammers in the stubbles had decreased since October, and would disappear once the fields were ploughed. Within the Reserve, birds were scarce along a rough route through the Chasm, over Goat Island to Rousdon, returning by different ‘paths’ and the Plateau. 15 species, including Marsh Tit, Bullfinch and Jay were contacted more than ten times in the two coastal squares SY28U and Z.

The Estuary came next. Tetrads 29K and L present marked contrasts, for in both an hour by the Axe needs to be paired with an hour among the roads and gardens of Seaton, Colyford and Colyton. Counting birds in towns is particularly difficult, and I missed the seven Blackcaps in the back garden of Ian Waite’s house in Durley Road! In contrast to the Axe tetrads one might expect that those in less varied ‘ordinary’ areas would be more similar to one another. However, for most species in the two inland tetrads east of Axmouth (Bindon and Rousdon) and two other ‘standard’ areas, north of Holyford and around Lower Bruckland, the hourly counts were very different. Only two species showed much consistency: Blackbirds with hourly counts of 26, 15, 23, 33, 28, 13, 13 and 16; and Robins, which varied between 9 and 15 per hour. Table 1 shows the ten species with the highest totals in these four tetrads, and the range in numbers counted per hour.

Table 1. Counts for ten common species in four ‘ordinary’ tetrads.

Conspicuous and gregarious species are the likeliest to have the highest counts, so that when a population estimate is wanted, some sort of conversion factor will be needed, and this must also take into account the habitats within the tetrad.
The coastal habitats of rocks, pebbles and cliffs between Culverhole and Beer hold few birds. Only 20 Curlew, 14 Rock Pipits, 10 Cormorants, 7 Oystercatchers, 4 Ravens and 3 Peregrine Falcons were found along 6 km of coast.

Table 2 – Numbers of the most counted species.

Inland, I surveyed all 11 tetrads in SY29 and 28 south of Colyton and mainly or partly within the 5 km radius. The 86 species found (and roving recorders will, no doubt, add more) can be loosely divided into five groups, bearing in mind my statement at the start that my enthusiasm is for common or widespread species in ‘ordinary’ countryside. On the evidence of my surveys so far, Sparrowhawks, like Woodcock and Lesser Redpolls, are decidedly scarce, and these birds form one group. The second group is made up of birds that are associated with the estuary or the sea and which are not in ‘ordinary’ country. That leaves three other groups. The first, made up of noticeable or numerous ones, is dominated by corvids, and is listed in Table 2.

A second group of five species (Song Thrush (90); Dunnock (83); Coal Tit (83); Magpie (46) and Buzzard (35)) are less numerous but still equally widespread. A third is made up of species that are still widespread, occurring in five or more tetrads, but with low populations or hard to find; they are listed in Table 3.

Table 3 – Widespread but scarce species.

There is another series of winter counts to be done (before the end of February), but later I will be particularly keen to find evidence of breeding for those species in the fifth group. This is an area in which roving recorders can be very helpful, and I can provide the appropriate forms, or they can be downloaded from www.birdatlas.net .