Data from Common Murre Die-off Surveys and Necropsies Following the North Pacific Marine Heatwave, 2015-2016

Beach Survey Counts: we counted all dead Common Murres observed on beaches while either walking along the length of the beach or motoring parallel to the beach in a skiff or small research vessel. For boat-based surveys, we motored along shore at a reasonable speed and distance given the visibility of birds and hazards near shore and scanned the beach by eye to count birds. For each surveyed beach we recorded: general area/region; beach name; names of surveyors; date/time of survey; distance searched (from GPS track line if possible); latitude/longitude of start/stop waypoints.

Necropsy instructions: Score shape and pattern of the outermost underwing primary coverts using Figure 532 in Pyle (2008). Coverts A, B, and C are associated with HY/SY birds, and D and E are associated with AHY/ASY birds. Measure mass: attach a Pesola either directly to a part of the bird (foot) or to a weighing bag and measure the mass of the bird while holding the ring of the pesola. If you used a bag, weigh the bag by itself afterwards, and record for later subtraction. Measure the natural/relaxed (unflattened) wing chord. Measure from the bend in the wing (wrist) to the longest tip of the wing to nearest mm. Measure the diagonal tarsus (length of tarsometatarsal bone): hold the leg so both the foot and tarsal joints are bent at right angles. Place the inner jaw of the calipers (or end of ruler) into the notch at the tarsal joint and slide the outer jaw until it contacts the end of the tarsus just where the foot bends and measure to the nearest mm. Measure the exposed culmen: place one jaw of calipers (or end of ruler) at the tip of the upper mandible and the other where fleshy part of bill meets the feathers, and then measure to the nearest mm. Measure the culmen depth: measure the bill depth at the deepest part of the bill to the nearest mm. Measure the headbill: place one jaw of calipers (or end of ruler) on the occipital condyle and the other at the tip of the bill, measure to the nearest mm. Assess condition of pectoral muscle based on shape: use standard codes (Figure 11; Van Franeker 2004) for scoring pectoral condition; 0=strongly emaciated, 1=emaciated, 2=moderate condition, and 3=good condition. Assess subcutaneous fat on breast between feathers on breast: use standard codes (Figure 11; Van Franeker 2004) for scoring subcutaneous fat; 0=no fat, 1=some fat, 2=fat, 3=very fat. Determine gender: determine gender by identifying the presence of testis or an ovary (Figure 1; Camphuysen and van Franeker 2007). If gender could not be determined, we categorized that as undetermined (Male=M, Female=F, Undetermined=U). Assess whether a bursa of Fabricius is present: the bursa of Fabricius is visible as a pouch on the outer wall of the cloaca, and it is only found in very young birds, it atrophies in sub-adults and is absent in mature birds (Figures 6 and 7; Camphuysen and van Franeker 2007). Assess stomach contents: cut open stomach, record contents.