The Society for the Prevention of Cruelty to Animals (SPCA) is on a manhunt for culprits behind two suspected cases of cruelty towards mynahs in the River Valley area.

In the first incident on Jan 25, a mynah was found on the ground floor of Block 78, Indus Road with its feet and neck tied with three different types of string.

The bird was alive when found by a passer-by, but had died by the time SPCA officers arrived, executive director Jaipal Singh Gill told The Straits Times.

Three days later, two mynahs were found with their legs bound together in a men's restroom at the nearby Delta House.

Members of a Buddhist meditation group found the birds, which appeared to be otherwise unharmed, and removed the string.

A report has been lodged with the Agri-Food and Veterinary Authority, which is investigating.

Dr Gill said that the incidents appeared to be deliberate acts of cruelty, adding that this is the first such case he has seen.

"It's not unheard of for a bird to get entangled - but three different strings makes it unlikely. One of the strings was also tied with triple knots. Because they happened in such close vicinity, our suspicion is that it is the same person or people responsible," he said.

SPCA volunteers went from door to door at Housing Board blocks along Indus Road on Tuesday night to hand out fliers with appeals for information.

The organisation is offering a $1,000 reward for information leading to the arrest and prosecution of those responsible.

The SPCA investigated 776 cases of alleged cruelty, which includes neglect and abandonment, from July 1, 2015 to June 30 last year. This is down from 846 cases for the same period spanning the previous year.

Dr Gill said that while the drop is not statistically significant, stronger enforcement by the authorities and stiffer penalties implemented against animal abusers in recent years have sent a clear message that abuse is not tolerated.

Under the Animals and Birds Act, those convicted of cruelty to animals face up to 18 months' imprisonment, a fine of up to $15,000 or both for the first offence.