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First it was sex, now it is the moonlight being blamed for keeping Alexandra's feral pigeon population alive.
After a failed poison-laced bait attack on the estimated 400-strong population living on the Alexandra bridge in July, the birds' keenness to concentrate on breeding instead was blamed.
About a fortnight ago, the New Zealand Transport Agency announced it would be back for another go, this time armed with air rifles, silencers and night vision goggles.
However, agency area manager John Jarvis said yesterday that second offensive had also so far failed to kill any birds, this time due to the moonlight.
It was just too light at night meaning the would-be snipers were visible to their prey.
When the birds failed to take the bait in July, Mr Jarvis said the agency was at a loss as to explain why as it was a ''tried and true'' method used around the world.
He thought it could have been because the birds were ''too busy trying to breed''.
The agency then changed tactics and brought in the hired guns, following approval from relevant authorities including the police and SPCA.
The birds roost on the Alexandra bridge, which crosses the Clutha River, and on the nearby historic bridge piers.
Mr Jarvis said their poo and roosting activities were corroding the structural steel of the bridge and so a cull was needed so agency staff could clean up the bridge and assess it for repairs or maintenance.
He said he expected ''more favourable'' conditions in the coming few weeks, although any bad weather could delay the operation further.
If that happened, ''it will just be deferred until things are good enough''.