Amid reports of pigeons dying, falling from the sky and acting like "zombies," the Moscow environmental prosecutor's office has begun an investigation into what some media outlets and bloggers have called a pigeon apocalypse.

The environmental prosecutor has ordered the department of environment protection and several municipal agencies to investigate the mass deaths of pigeons and other birds in Moscow, according to the newspaper Izvestiya, which quotes Timur Brudastov, a senior judicial adviser at the prosecutor's office.

Brudastov notes that, according to the federal service for veterinary and phytosanitary surveillance, Moscow has become a "hotbed" of Newcastle disease, a bird disease that can be transmitted to humans.

"We're getting different information. Someone will write that seven birds have died in the city, while others tell us about them dying en masse," Brudastov said.

Although not all pigeons are affected, some have reportedly been acting as if drugged, stumbling and reacting slowly to humans, or else flying into the faces of passersby and falling to the ground.

"Before death, they start to resemble zombies: they lose their orientation and fly without a sense of direction, then fall, already lacking the strength to get up," wrote Konstantin Ranks, a science columnist at the website Slon.ru.

Some cases of salmonella infection had also been found in dead birds, Aleksei Alekseyenko, an aide at the Federal Service for Veterinary and Phytosanitary Surveillance, told Izvestiya. He said the combination of hot weather and the presence of an infected bird had probably led to the outbreak of disease, but added that the epidemic was already coming to an end.

Moreover, the more dangerous diseases of bird flu and parrot fever had not been found, Alekseyenko added.

One veterinarian, Natalya Anisimova, told the Russian TV channel Rain last week that her clinic had received many calls about dead birds, but such deaths happened every summer. Anisimova agreed, however, that the problem could be growing more acute because the pigeon population was growing.

Moscow has had incidences of mass bird deaths in the past, including one in 2010, which experts blamed on smog.

Some bloggers have said the pigeon fatalities mark the coming of "the end times", pointing to the tsarist-era mystic Grigory Rasputin's alleged prediction of the apocalypse on 23 August 2013, according to the newspaper Komsomolskaya Pravda.