LOUISIANA BIRD RECORDS COMMITTEE

REPORT FORM

1. English and Scientific names: Parasitic Jaeger (Stercorarius parasiticus)

2. Number of individuals, sexes, ages, general plumage (e.g., 2 in alternate plumage): 1 (one) in juvenile (first basic, sensu Howell et al. 2003) plumage. Dark(ish) morph.

3. Locality: LOUISIANA: (parish) Plaquemines

Specific Locality: Mississippi Canyon

4. Date(s) when observed: 25 Sept 2011 (note date of 26 Sept 2011 on LBRC website and other reports is incorrect)

5. Time(s) of day when observed: 9:45am

6. Reporting observer and address: Erik I. Johnson, 102 Goodwood Cir., Lafayette, LA 70508

7. Other observers accompanying reporter who also identified the bird(s): Justin Bosler, Devin Bosler, David Muth, Dave Patton, Dan Purrington, Joelle Finley, David Ringer, Melanie Driscoll, Jane Patterson; and about 10 other birders.

8. Other observers who independently identified the bird(s): none

9. Light conditions (position of bird in relation to shade and to direction and amount of light): clear and sunny, sun at various angles as we followed the bird

10. Optical equipment (type, power, condition): Swarovski 10x42 EL, photographed with Nikon D100 and 80-400 mm ED Nikon lens

11. Distance to bird(s): 30+ m

12. Duration of observation: 10 minutes

13. Habitat: blue water (pelagic)

14. Behavior of bird / circumstances of observation (flying, feeding, resting; include and stress habits used in identification; relate events surrounding observation): Found loafing on water, but wary and flushed before we could get really close several times. At one point, briefly pursued a Bridled Tern before eventually flying off.

15. Description (include only what was actually seen, not what "should" have been seen; include if possible: total length/relative size compared to other familiar species, body bulk, shape, proportions, bill, eye, leg, and plumage characteristics. Stress features that separate it from similar species): Very dark overall with cinnamon-colored barring on undertail coverts and weak spotting/barring on underwing. Narrow cinnamon edging on dark chocolate black upperparts. Head all dark and seemingly smallish, and also smallish billed. Under-primary coverts seemed paler at the base. Central rects longer than outer rects and seem pointed - this is best seen in a photo by Justin Bosler.

Using photoshop, I measured the wing-span in the photo with the Bridled Tern and compared the ratio of the jaeger to the tern in the photo with measurements provided in Nat. Geog. Birds of North America, recognizing caveats of whether the wings were fully spread, if the birds were on the same plane, and the unknown within-species variation in this measure. In any case, Pomarine:Bridled is 1.6 and Parasitic: Bridled is 1.4. This jaeger is 1.5.

16. Voice: not heard

17. Similar species (include how they were eliminated by your observation): Long-tailed Jaeger and Pomarine Jaeger should typically have white (not cinnamon) and dark undertail coverts. Pointed central rects would also best fit Parasitic, despite conflicting other structural (seemingly bulky body and bill for Parasitic) and plumage (unstreaked face and second white “flash” in under-primary coverts).

18. Photographs or tape recordings obtained? (by whom? attached?): Photos: http://erikjohnsonphotography.blogspot.com/2011/09/pelagic-trip-south-of-venice-la.html

19. Previous experience with this species: Very little experience with jaegers in general, about even with Pomarine (in LA) and Parasitic (in NE US). Not enough to feel confident in terms of great structural and plumage variation in these species.

20. Identification aids: (list books, illustrations, other birders, etc. used in identification):

a. at time of observation: Sibley Guide

b. after observation: Nat. Geog. Birds of North America, Pyle’s Guide (2008), Kaufman’s Advanced Birding Guide, internet photos, discussions and circulating photos with others in the group, discussions with others with more experience (Marshall Iliff, Brian Sullivan, Ryan Terrill, and Van Remsen)

21. This description is written from: __X__ notes made during the observation (_____notes attached?);__X__notes made after the observation (date: next couple days); _____memory.

22. Are you positive of your identification if not, explain: Not really. Others, including Iliff, Sullivan, Terrill, and Remsen, had been pushing Pomarine Jaeger until they saw Justin’s photos of the pointed central rects. I feel the plumage clues are ambiguous and I don’t know how to weight the relative importance of these clues. For example, I have had a hard time finding photos with cinnamon-barred undertail coverts in Pomarine, and similarly have had a hard time finding pale-based under-primary coverts in Parasitic. The bill looks small and thin in some photos, but the body looks bulky and barrel-chested in others. Does the size comparison with the Bridled Tern help? Is there a remote possibility of hybridization?

23. Signature of reporter: Erik I. Johnson, 25 Oct 2011, 9:50pm