Animal campaigners in Inverness said the juvenile herring gull was targeted at close range.
The bird had to be put down after it was found with a bolt through its neck in the city's Charleston area yesterday morning.
Scottish SPCA chief inspector Iain Allan said: "This was a sickening incident which would have caused this bird a great deal of pain and suffering.
"We suspect this was a deliberate attack with the intention of causing harm to a defenceless animal.
"This incident is extremely concerning and we would urge anyone with information to contact us as soon as possible."
Information can be reported to the Scottish SPCA animal helpline on 03000 999 999.