An intruder at the spire of Norwich cathedral could prompt 'sibling rivalry' among the newborn peregrine chicks as food may become scarce, according to the Hawk and Owl Trust.
The last sighting of the domestic female was last Sunday, with a stronger, younger usurper from Bath harassing her and preventing her feeding the young.
Following an infection in the young male, spotted this week, the Hawk and Owl Trust are concerned for his future, but say they cannot intervene.
A spokesman for the Hawk and Owl Trust said: 'On Saturday 14th May, a large dominant female bird was seen visiting the Cathedral Spire at Norwich. At that point our resident female appeared to be submissive to the female and was taking no action against the 'intruder'. At that time the chicks were still being fed by both the male and the female.
'The following morning, it was noted that the intruding female had a blue ring on her left leg, at the time the letters on it could not be distinguished. However it was seen that she was starting to have a noticeable effect on our female throughout the day, harassing her and preventing her from delivering food to the chicks. The last noted time on our webcams where our female was seen on the platform was at 8.29am on Sunday 15th May.
'On Monday 16th May, the day of the ringing of our Norwich chicks, the letters on the ring became visible and were confirmed as GA, this is a bird that hatched and was ringed at St. John's Church in Bath in 2013, the sister project to our Norwich peregrines. GA was seen around the cathedral and on the spire. At one point seen on the window apex above the nest box and throughout the day catching prey, plucking and storing it on the very top of the spire. The Norwich resident female was not seen at all throughout Monday and all feeds to the chicks were delivered by the male.
'The 'intruding' peregrine, GA, is of breeding age, when she was ringed in Bath in 2013 she was described as 'a large, feisty female'. However this is not the first time she has visited Norwich Cathedral, as she made an appearance in Norwich in the summer of 2015 and has appeared several times over the last winter. Sightings in the local area have also been reported showing she has been around in Norfolk over the last couple of weeks and we believe she may have been roosting in the nest box that we recently installed at Wymondham Abbey in February this year, as a blue ringed female had been observed.
'With the introduction of GA into the arena here at Norwich, our female seems to have been chased away from the Cathedral, though she may still be in the area. The male now appears to have become the sole provider of food. He will continue to bring in food as often as he can, however as the chicks continue to grow and develop over the next 10 days or so, they will require increasing amounts of food. It is in this situation that 'nature, red in tooth and claw' may be seen in action and on our cameras. At this stage sibling rivalry may occur and the strongest and fittest of the chicks will pick on the smallest and weakest if food is in short supply.
'The policy of the Hawk and Owl Trust, confirmed by Conservation Officer Nigel Middleton is that we will not intervene should this occur. This differs from the situation earlier in the week when the chicks were ringed by a licensed BTO ringer. On that occasion a veterinary surgeon was present to take samples for DNA and throat swabs as part of a research project into DNA profiling. It was a veterinary decision based on animal welfare considerations to treat a sick chick.
'Peregrines are a Schedule 1 species of bird that are protected by law and for the Hawk and Owl Trust to intervene would require us to hold the relevant licence to do so. To justify obtaining such a licence there would need to be evidence of a complete abandonment of the chicks by both the parents. As the adult male is still seen to be feeding the chicks as best he can, what is happening now would be regarded as a natural occurrence and as such would not justify intervention from the Hawk and Owl Trust.'
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