Dynamic measurements of black oystercatcher (Haematopus bachmani) predation on mussels (Mytilus californianus)

A black oystercatcher foraging in central California

Myself and co-author Wes Dowd have a new paper out in the journal Invertebrate Biology detailing a set of observations we made of black oystercatchers attacking a set of mussels that were part of an experiment we were running. The mussels in our experiment were wearing a set of sensors, including an internal temperature sensor, a valve gape sensor (aka a ‘valvometer’), and a 3-axis accelerometer and magnetometer sensor. These mussels were part of a bed of live mussels (image below) that we set out in the intertidal zone at Hopkins Marine Station.

Our experimental mussel bed

During our experiment with the mussels (see Miller & Dowd, 2017 and Gleason et al., 2017 for the results), one or more oystercatchers decided that our tray of mussels looked like a great meal, and proceeded to attack and eat several of the mussels on the plate, including 3 mussels that had sensors mounted on them. The data from these attacks, including the valve gape of the mussels and the accelerations imparted on the mussels by the birds, are described in the current paper. Although the dataset is small (only 3 documented attacks), these are the only directly-measured data of mussel disposition before and during an oystercatcher attack. The oystercatchers went after the mussels that were widest-gaped on the plate (based on the gape sensor data), and chose to attack the mussels as they were re-opening after being closed for several hours during low tide.

After the first two days of attacks, I put a waterproof timelapse camera out on the rock above our mussel bed, and managed to capture the image below of the oystercatcher actively attacking the third mussel (based on the matching timestamps between the image and the high accelerations on the mussel datalogger).

A clever oystercatch attacking one of our experimental mussels.

Using the accelerometer and magnetometer data, we recreated the (approximate) position of a mussel before and during the attack. The video below shows one of those reconstructions. It’s important to note that the depicted shell orientations are only approximate, since it’s difficult to estimate the orientation of the mussel during instances of high acceleration. The net acceleration on the mussel (subtracting off gravitational acceleration) is shown in the upper right of the video, and the video plays the action back in real time.