Bird Survey Results 2020

Birds on the Thames Basin Heaths SPA in 2020

The Thames Basin Heaths Special Protection Area (SPA) was proposed more than 20 years ago to protect three species of birds – nightjar, woodlark and Dartford warbler – declining across Europe. All three breed in internationally important numbers on the remaining areas of lowland heathland habitat that occur in the Thames Basin area across Surrey, Hampshire and Berkshire. Numbers are monitored annually for Natural England by a team of volunteers coordinated by 2Js Ecology.

We are pleased to report that in 2020, despite the difficulties arising from the COVID-19 pandemic, survey coverage was good and numbers of all three species were at very high levels across the SPA.

The table below compares the 2020 totals with the numbers that informed the notification of the SPA.

Bird species No. of pairs at SPA notification Year of notification survey No. of pairs in 2020 Percentage change
Nightjar 264 1998-99 404 +53
Woodlark 149 1997 167 +12
Dartford warbler 445 1999 711 +60


The populations of nightjar and Dartford warbler reached record levels in 2020. Woodlark numbers continued to recover from recent low points but remain some way below the total of 228 pairs reached in 2007. The reasons for the high population levels are a combination of management of the habitat to maintain the conditions in which these species thrive and a series of recent mild winters. Dartford Warbler in particular suffers high mortality during spells of cold and, especially, snowy weather but is able to quickly recover in years following mild winters, as in 2018/19 and 2019/20.

The SPA comprises 13 component Sites of Special Scientific Interest (SSSIs) across three counties. Seven of the sites are extensive with areas between 673 and 1696 ha, while the remaining six are smaller with areas between 66 and 256 ha. Nonetheless, all three species occurred on each of the component SSSIs except that woodlarks, the rarest of the three, were not found on Eelmoor Marsh, Ockham to Wisley Commons and Sandhurst to Owlsmoor. This demonstrates the importance of protecting even small areas of heathland close to the major urban centres in this area.

The SPA is also important for other wildlife including the sand lizard and smooth snake as well as a large variety of invertebrates such as the silver-studded blue butterfly and the great fox-spider, which was recently rediscovered after not being seen in the UK for 27 years. Those of us living in the area are very fortunate to have such attractive and biodiverse habitat on our doorstep.

Thanks are due to all the landowners and land managers including the Ministry of Defence, Forestry England, local authorities, the Wildlife Trusts and the RSPB for helping to preserve this precious habitat. We also want to thank our team of volunteers without which these valuable data would not be obtained.

John Clark & John Eyre
2Js Ecology




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