Seabirds are starving to death due to North Atlantic winter cyclones

A study focused on the deaths of seabirds during these events in the winter months

by Lorenzo Ciotti
Seabirds are starving to death due to North Atlantic winter cyclones

An Atlantic hurricane is a tropical cyclone that forms in the Atlantic Ocean, usually in the Northern Hemisphere, in summer or autumn, with sustained winds for one minute at 64 knots / 32.9 m / s. When referring to hurricanes, the Atlantic generally refers to the entire Atlantic basin, which includes the north of the Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico.

Most tropical storms and hurricanes occur between 1 June and 30 November. The US National Hurricane Center monitors the basin and publishes reports, observing and warning of tropical weather systems forming in the Atlantic basin.

Tropical disturbances that reach tropical storm intensity are named according to a predetermined list. On average there are 10 storms that reach this intensity and are therefore named; of these, on average 6 become hurricanes and 3 become major hurricanes (category 3 or higher).

The peak of climatological activity is around 10 September. A study focused on the deaths of seabirds during these events in the winter months. The study is titled North Atlantic winter cyclones starve seabirds, and was published in the Current biology.

Researchers say: "Each winter, the North Atlantic Ocean is the stage for numerous cyclones, the most severe ones leading to seabird mass-mortality events called winter wrecks. During these, thousands of emaciated seabird carcasses are washed ashore along European and North American coasts.

Winter cyclones can therefore shape seabird population dynamics by affecting survival rates as well as the body condition of surviving individuals and thus their future reproduction. However, most often the geographic origins of impacted seabirds and the causes of their deaths remain unclear.

We performed the first ocean-basin scale assessment of cyclone exposure in a seabird community by coupling winter tracking data for ∼1,500 individuals of five key North Atlantic seabird species and cyclone locations.

We then explored the energetic consequences of different cyclonic conditions using a mechanistic bioenergetics model and tested the hypothesis that cyclones dramatically increase seabird energy requirements. We demonstrated that cyclones of high intensity impacted birds from all studied species and breeding colonies during winter but especially those aggregating in the Labrador Sea, the Davis Strait, the surroundings of Iceland, and the Barents Sea.

Our broad-scale analyses suggested that cyclonic conditions do not increase seabird energy requirements, implying that they die because of the unavailability of their prey and/or their inability to feed during cyclones.

Our study provides essential information on seabird cyclone exposure in a context of marked cyclone regime changes due to global warming"