A robin perches on a spade handle in a garden on a rainy day in Lixwm, north Wales. Researchers said this week that when European robins are subjected to human-produced noise, their behaviour changes. (Photo by DGDImages/Alamy Live News)

A Saudi police officer receives emergency calls at a call center, ahead of the Hajj pilgrimage in the Muslim holy city of Mecca, Saudi Arabia, Tuesday, August 6, 2019. The hajj occurs once a year during the Islamic lunar month of Dhul-Hijja, the 12th and final month of the Islamic calendar year. (Photo by Amr Nabil/AP Photo)

Argentinian twin dancers Nicolas Filipeli and German Filipeli perform during the Tango Stage final competition at the Tango Dance World Championship in Buenos Aires on August 21, 2019. (Photo by Ronaldo Schemidt/AFP Photo)

A conductor (C) collects fares from candy floss sellers as they travel in a tram to a marketplace early morning in Kolkata, India, December 23, 2015. (Photo by Rupak De Chowdhuri/Reuters)

U.S. Army helicopters providing support for U.S. ground troops fly into a staging area fifty miles northeast of Saigon, Vietnam, August 28, 1966. Helicopter fuel is stored in the large rubber tanks, foreground. (Photo by Henri Huet/AP Photo)

Elderly women wait for customers as they sell their self-made food products at a street market, with a graffiti depicting Russian President Vladimir Putin on the wall of a house seen in the background, in the town of Kashira, outside Moscow, Russia on October 10, 2017. (Photo by Andrey Volkov/Reuters)

A woman picks marigold flowers used to make garlands and offer prayers, before selling them to the market for the Tihar festival, also called Diwali, in Kathmandu, Nepal on October 17, 2017. (Photo by Navesh Chitrakar/Reuters)

A dog walks past a mural by street artist Alex Martinez outside a shop which sells bags at Psiri area, central Athens, on Thursday, January 25, 2018. (Photo by Petros Giannakouris/AP Photo)