The painting down at the Rea Brook was designed and created by local artist Mat Sewell in a bid to stop the area being targeted by graffiti tagging.
However just six months after the mural was completed, it has been ruined.
Matt Wilcoxon, Shrewsbury Town Council's countryside and greenspace team leader, said: "The mural was painted by Matt Sewell last year as the area was looking a bit run down and we hoped that it would stop the tagging, as it has done under the cycle way further down the brook.
"Artwork usually stops the tagging because it's something people generally do on blank spaces. Sadly this time it didn't deter them."
It is hoped that the artist can touch up the painting and restore it to its former glory.
The bird, which is popular with bird spotters and dog walkers, is commonly referred to as an albino magpie but Matt said it is actually leucistic - meaning he lacks any pigmentation.
Matt added: "This amazing bird has been a regular around the Rea Brook Valley Nature Reserve for the last four years and seems to be socialising well with the other magpies.
"We saw him a couple of times at a distance and at first couldn't tell what it was. Initially I thought it could have been an escaped cockatoo because there was no black on him at all.
"A clear picture of him was published in a local magazine and that's when we identified that he was in fact a magpie. He's been there every since seems to be doing really well.
"It has something called leucism, which can be seen in many birds, although usually just on a few feathers. It is caused by a gene that disrupts the production of colour pigment in skin, fur or feathers of animals. Where this occurs to a great extent, it is often confused with albinism. Albinos are much rarer and have a lack of the melanin pigment only, causing red eyes as well as colour differences."
The magpie isn't the only example of leucism on the town council's nature reserves, however. There is also a white headed blackbird at Becks Field opposite the Quarry and a jackdaw with a completely white tail at Monkmoor Community Woodland.