"For the first 14 years it was the second most common species but it has
since declined. ........ The abundance has declined smoothly and markedly,
particularly from Years 6 to 21. This is clearly a valid result as this is a
widespread species. However, it could be a long-term undulation as the
population was increasing from Years 1 to 6. Breeding records were highest in
the mid 1980s and have declined since."
Following other comments, yes the Collared Sparrowhawk's population has had a
dramatic rise over the period that the House Sparrow has declined. I hadn't
thought of any connection previously. If there is any connection, it can only be
a predator impact on prey, not the other way around.
Philip
