Paul Salmon, senior project manager with National Highways, said: “Protecting the environment is central to both the design and construction of our scheme.
“Features like this help to improve habitat connectivity and support local wildlife.”
He added that they had a deep understanding of the local environment as a result of extensive survey work.
The aim of the road project is to reduce congestion and speed up journey times, with about 80,000 drivers using the Black Cat roundabout each weekday.
The new 10-mile (16km) A421 dual carriageway is due to open in Spring 2027.