By Yaya Callahan, NSF REU INTERN
The Seabird Oceanography Lab is almost midway through the field season here at Yaquina Head Outstanding Natural Area. The murres have not been able to incubate eggs this year and we are expecting a year of no reproductive success. We are continuing our monitoring effort and are anticipating starting diet photography efforts soon at the small colony located in Depoe Bay.
When observation began in late May at Yaquina Head, we saw the murres repeatedly flushed from the main nesting site Colony Rock by eagles. Often two sub adult and two adult eagles would also flush Lion’s Head, Seal, and Stegosaurus Rock, and the murres would not return to these areas as quickly. By June, later then we expected, murres began to settle and we spotted birds with eggs on Colony Rock. Although the majority of Colony Rock was covered with birds, two locations at the eastern side closest to eagle’s roost remained unoccupied.
About a week later the avian predator disturbances spiked again. The first one that led to considerable undoing of nesting progress was on June 13th, when three separate groups of turkey vultures flushed murres from the colony. Only one of these groups of vultures was accompanied by bald eagles. These disturbances allowed western gulls to opportunistically take over 30 murre eggs – even dropping some on the ground around the lighthouse. The gull flock continued to grow as on the 17th, we estimated over 50 gulls flying overhead. From then on – apart from the chaotic observation day on June 22nd — it only took one disturbance each observation period for the murres to be completely cleared off. Each time their numbers on colony rock dwindled. When they were present on the rock many were standing and not in their nesting position.
In early July we typically have murre chicks, but this year Colony Rock has been devoid of adult murres and eggs for over a week now. Murres are continuing to raft in the water nearby the colony. There have been some murres attending Stegosaurus Rock and South Headland however they aren’t nesting. Normally, eagle disturbances decline through June, but this year they have been continuing. Additionally, winter conditions persisted through May and upwelling was delayed until June. This likely contributed to the inability of the murres to settle and incubate eggs. Upwelling brings cold nutrient-rich water to the surface that fuels primary productivity and the forage fish murres depend on. Upwelling typically initiates in mid-April prior to when murres lay their eggs.
Unfortunately, the number of nesting Brandt’s and Pelagic cormorants are low this year. Eagles do not disturb them like they do the murres though many gulls roost on Flat Rock where the Brandt’s are nesting. Flat Rock has quite the dynamic rise and fall in nests; On July 6th we had spotted 35 nests. On June 29th we realized that almost half of these had been abandoned – mostly on the Western and top half of the rock. We are currently following 17 active Brandt’s nests. Additionally, we have two Pelagic cormorant nests on Stegosaurus Rock and we are following 15 Pelagic cormorant nests on South Headland.
On the bright side there are three healthy looking chicks on South Headland and we are expecting more on Flat Rock. We’ll make sure to monitor these chicks and keep an eye out for murres though.
See you again for our next update in August!