A rogue bird has threatened to destroy the clutch of four peregrine falcon eggs being nurtured on the spire of Norwich Cathedral.
A female peregrine flushed the father from the nest and then indicated it was "toying with the idea of breaking them," said the Hawk and Owl Trust.
It eventually withdrew from the nest when the adult male made "high speed low passes over her head".
The clutch of four eggs is the third successful year of laying for Norwich's breeding pair. They are now 12 days into what is expected to be a 34-day incubation period, said experts.
The DP peregrine, ringed in 2012, first showed an interest in the Norwich nest some weeks ago.