ML30041331

Age and sex

Immature Unknown sex - 1

Behaviors

Flying

Observation details

Clear jaeger observed chasing Red-billed gull. It appeared to be a dark immature. White under wing, bill pattern, knobs on tail, barred belly, and flight style and size eliminated a gull. The best way was a combination of the dark body and small size, unlike any gull in NZ. Identification as an Arctic was based on several details. First, the flight style. The flight style was not extremely buoyant like a Long-tailed, however there was frequent wing beats, unlike the slower ones of a Pomarine. Secondly, the structure was not huge chested, broad winged like a Pomarine, but not extremely thin winged like a Long-tailed. Thirdly, the knobs on the end of the tail were pointed, not rounded as in Pomarine. Fourthly, the primaries had four feathers with a white shaft, more than expected for a Long-tailed. There was only one white 'flash' on the underwing, unlike the 'double flash' on Pomarine (I'm not sure what the technical terms for these are). The under tail coverts were wavy bars, however that contrasted with the base color. There were several warm cinnamon tones on the nape, unlike Long-tailed. The bill color and shape were also critical, the bird only having a small black tip to the bill. The bill shape was long and thin, not stout like a Long-tailed or thick like a Pomarine. Finally, the Arctic seems like the most probable Jaeger inland in NZ in the winter. Long-tailed is extremely rare, Pomarine is a rare summer visitor to the South Island, while Arctic is an uncommon in summer, and rarely immatures overwinter (Falla, Sibson, ). Consequently, all of the field marks add up to a Arctic over other Jaegers, as well as probability. I'll attach poor photos as soon as I can

Technical information

Model

Canon EOS DIGITAL REBEL XT

ISO

400

Focal length

250 mm

Flash

Flash did not fire, auto

f-stop

f/8.0

Shutter speed

1/500 sec

Dimensions

3456 pixels x 2304 pixels

Original file size

2.73 MB