Here is a sample of the updates I have been writing on the Common Murre field season at Yaquina Head Outstanding Natural Area:
It has been an exciting two weeks for murre surveys with unexpected trends and behaviors.
Number of mapped eggs within our 12 study plots increased in both colonies, totaling 115 eggs on Flat Top and 106 eggs on Colony Rock. But eagle disturbance has been high and we have lost 53 of these eggs on Flat Top and 26 eggs on Colony Rock. Flat Top has been disturbed so vigorously, that an entire plot on the south end of the rock has been cleared. This plot was coincidentally the one with the most mapped eggs on Flat Top.
Surprisingly and contrary to last year’s field season, sub-adult bald eagles have caused most of the disturbances. Out of twenty-two disturbances recorded, eighteen have been due to sub-adult and only four have been caused by adult eagles. During observations, these sub-adults have only taken three murres; and the adult eagles have taken one. The inexperienced sub-adults rarely land on the colonies, but instead have started landing on the headland south of Flat Top for several hours. Additionally, we have had a record of bald eagle presence on such headland, seeing up to five eagles at once. In this occasion there was only one adult eagle among four sub-adults.
Predation of eggs recorded by the opportunistic Western gulls has been fierce. Gulls have been observed continuously taking eggs, cracking them, and going back for more; a process in which we saw 21 eggs get taken from north of Colony Rock in about three minutes. However, most eggs within plots on Colony Rock have been doing better than initially expected, when egg laying was delayed due to eagle disturbances. Now, individuals on this rock are more reluctant to evacuate, clearing only 5% or less, even when an adult bald eagle is on the rock.
This week’s disturbances will be a determining factor in the common murres’s reproductive success. If eagles continue to disturb the colonies in groups of four or more, as we have recorded, murre colonies may be greatly impacted, especially on Flat Top.