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Not long ago, a species of seabird called Cassin's auklets died in unprecedented numbers on the western shores of the United States.Scientists do not know exactly what caused their death, but there are several factors that may have contributed to the die-off.

Increased Competition

First of all, it is known that the number of auklets born the summer before the die-off was significantly higher than average. With such a large population it is possible that the young auklets were simply competing with each other for a limited amount of food. With increased competition for resources, it could be that food was spread thin across the population. Many birds were unable to find enough food and died off before the proper balance between the number of auklets and food resources was restored

Virus

Another possibility is that the birds were affected by a virus. A few years ago in the same area, populations of sea animals known as sea stars were devastated by a virus that caused large numbers of them to become infected and die. The particular virus found to have caused those deaths is known to be excellent at adapting to different hosts. It is possible, therefore, that the auklets contracted the virus after coming into contact with or eating one or more infected species.

Zooplankton

Finally, scientists have recently discovered a large patch of unusually warm water, hundreds of miles across. This patch formed close to the time the die-off started. The change in water temperature likely had an effect on the populations of tiny sea creatures called zooplankton that auklets feed on. One study found that the zooplankton in that area of warmer water had become smaller and less nutritious than usual. This lack of nutrition may have contributed to the die-off.

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