The deaths of hundreds of wild birds along Mexico's Pacific coast were likely caused by the El Niño climate phenomenon, local authorities said on Thursday, as the country and its surrounding oceans face an intense heat wave.

Authorities had initially suspected bird flu, but a joint effort from the country’s agriculture and environment ministries concluded the most likely reason was warmer oceans resulting from El Niño.

The periodic natural phenomenon, which lasts between months and years, warms the Pacific Ocean fuelling tropical cyclones, floods and rainfall across the Americas and elsewhere.

The U.S. National Oceanic and Atmospheric Administration (NOAA) earlier this month declared that an El Nino is now under way, after three years dominated by the cooler La Nina pattern.