Dec 17 2021

Heartwood Forest’s wildlife highlights

It’s been just over a decade since the Woodland Trust acquired the site, with the planting of 600,000 trees beginning on the bare and mostly arable land in 2009 and finishing in March 2018.


We have been lucky enough to work with a fantastic team of dedicated volunteer wildlife monitors from the start who have monitored and recorded a variety of wildlife across Heartwood Forest over that period.


Here are some of the wildlife monitoring highlights at Heartwood from 2009- 2020…


  •  The total butterfly count has increased from 1,200 in 2010, to 4,000 in 2018 – 2020 – a more than 3-fold increase. Small Heath has increased from 0 to 450; Marbled White from 20 to 500; and we now have significant populations of the rare Small Blue and Purple Emperor.
  • The total number of birds recorded in the Breeding Birds Survey was 400 in 2010 and more than doubled to 890 in 2019.
  • Skylarks increased from 75 counted in 2009 to a maximum of 160 in 2016.  Numbers have since fallen back to about 90 as some of their nest sites now have young trees growing in them.
  • Blackcap numbers have increased from 7 to 17; Whitethroat from 12 to 38; and Willow Warbler, a rare species in Hertfordshire, from 1 to 14.
  • Rare sightings have included a Hen Harrier, Great Grey Shrike, Grasshopper Warbler and Hawfinches.
  • Since 2012 19 kestrel chicks and 60 barn owlets have been ringed in Heartwood boxes.
  • Small mammal surveys (which monitor mice, voles and shrews) have found 8 species including the rare Yellow-necked Mouse and Harvest Mice.
  • Regular bat monitoring has revealed 8 species of bat, including the rare Barbastelle.
  • Common lizards have been found in the last few years.
  • Over 200 species of flowering plant have been recorded, with Common Spotted and Pyramidal Orchids beginning to appear all over the site.
  • Although non-native, and generally well known to the south of England, the exotic-looking wasp spider was spotted for the very first time at the site during 2015.
  • Heartwood is also one of only 3 sites in Hertfordshire to have Stripe-winged Grasshoppers.

 A huge thank you to this dedicated volunteer team for recording such valuable information!




Jenny Carpenter – Engagement and Communications Officer (Central England)


Image credits

Grasshopper warbler John Bridges/WTML

Purple Emperor butterfly Matt Berry/ WTML

Pyramidal orchid John Bridges/ WTML

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