338] GeneralNotes J.Field Ornithol. Autumn 1981 largelyineffective in reducingthe rat population.Institution of a vigorouspoisoning and trapping program on Midway Atoll is needed to prevent the exterminationof the Bonin Petrel as a successfulbreeding species there. Summary.--OneBonin Petrel colony was free of rat predation while others suffered nearly total predation. The continuousincubation, orientation of the incubating petrel with respectto the tunnel entrance,procellariiform odor, and learning are discussedin relation to rat predation. If the present rate of egg predation persists,the Bonin Petrel will soonbe lost as a successfulbreeding species on Midway Atoll. Acknowledgments.---Ourstay on MidwayAtoll wassupported by NationalScience Foun- dation Grant #PCM 76-12351-A01administered by G. C. Whittow.We are grateful to CDR Kuhneman and CDR Barnes,Commanding Officers, for assistanceduring our stay at the U.S. Naval Air Facility,Midway Atoll. Specialthanks are due ENS Immel and the basegame warden staff for invaluableaid and transportationto EasternIsland. LITERATURE CITED

ALSA•r•r,R. S. 1945. (Noteson the statusof birds on Midway Island). Elepaio 5:49-51. BOERSMA,P. D., ANt)N. T. W•EEI•WR•C•r. 1979. Egg neglectin the Procellariiformes: reproductiveadaptations in the Fork-tailedStorm-Petrel. Condor 81:157-165. F•s•Eg, H. I. 1961. Weightsand measurementsof organsof Bonin Island Petrels,Pter- odromaleucoptera hypoleuca. Auk 78:269-271. FI•EE•r,R. R. 1972. Nestingsuccess of the Red-tailedTropicbird on Kure Atoll. Auk 89:651-659. GV,AN•r, G. S., T. N. PE•r•rrr,H. RAIN, G. C. W•iTrow, ^Nr) C. V. PAC^NELI•.In press. Regulationof water lossfrom Bonin Petrel (Pterodromahypoleuca) eggs. Auk. HowE•, T. R. 1978a. Reproductivebehavior and morphologicaladaptations of the Red- tailed Tropicbird. Natl. GeographicSoc. Res. Reports, 1969 projects:261-273. ß 1978b. Ecologyand reproductivebehavior of the White, or Fairy, Tern. Natl. GeographicSoc. Res. Reports, 1969 projects:274-284. --, and G. A. Bartholomew. 1961. Temperature regulationin nestingBonin Island Petrels,Wedge-tailed Shearwaters, and ChristmasIsland Shearwaters.Auk 78:343- 354. KEPI•Eg,C. B. 1967. Polynesianrat predationon nestingLaysan Albatrosses and other Pacific seabirds. Auk 84:426-430. LUDWIG,J.P., C. E. LUDWIG,AND S. I. APFELBAUM.1979. Midway Island survey1-24 February 1979. EcologicalResearch Services, Iron River, Michigan,52pp. Mt•NgO,G. C. 1945. The smallbirds of Midway. Elepaio6:13-14. RAHN,H., R. A. ACKERMAN,AND C. V. PAGANELLI.1977. Humidity in the aviannest and egg water lossduring incubation.Physiol. Zool. 50:269-283. ROBBINS,C. S. 1966. Birds and aircraft on Midway Island, 1959-63 investigations.U.S. Fish and Wildlife Service,Special Sci. Rep.-Wildlife No. 85. Wooow^gr), P. W. 1972. The natural history of Kure Atoll, NorthwesternHawaiian Islands.Atoll ResearchBulletin No. 164. SmithsonianInstitution, Washington,D.C. GILBERTS. GRANT,TED N. PETTIT,AND G. CAUSEYWHITTOW, Department of Physiology, JohnA. BurnsSchool of Medicine, University of Hawaii, Honolulu, Hawaii 96822 (Presentaddress GSG:Department of Physiology,State University of New York,Buffalo, New York14214). Re- ceived5 Sept. 1980; accepted21 July 1981.

On the Slit Pupil of the Black Skimmer (Rynchopsniger).--The Black Skimmer is the only bird known to closethe pupil into the form of a vertical slit. The slit pupil was first noted by Taczanowski(Proc. Zool. Soc.Lond., 1874:563)and waslater discussedby Wetmore (Proc. Biol. Soc. Wash. 32:195, 1919) as follows:"The opening was reduced very little in its verticallength but narrowedgreatly so that whencontracted the opening wasnearly as high aswhen expanded. When fully openedthe upper and lowerpoints of the pupillar aperture were marked by distinctangles so that even at this time the opening was not circular." Vol.52, No. 4 GeneralNotes [339

1 2 3 4 5

F•oum• 1. Eye openingsand pupils (black)of the Black Skimmer and Common Tern under different light intensities.A, CommonTern (adult); B, BlackSkimmer (adult female); C, Black Skimmer/juvenile). Incident light readingsin lux: (1) 0, (2) 530, (3) 8250, (4) 93,500,(5) 140,800.Each row representsa singleindividual. Photographs takenat samedistance from eachsubject. The viewis not directlyinto the pupil but slightlyto one side.Diamonds represent missing data.

Walls (The Vertebrate Eye and its Adaptive Radiation, Cranbrook Inst. Sci. Bull. 19:219, 1942) pointedout that a slit pupil perse is not an adaptationfor improvedvision in dim light, althoughit occursprimarily in nocturnalor aquaticvertebrates. Its valueis rather in achievinga greaterreduction of the pupil in thosenocturnal animals that must protectthe iris in bright sunlight.The pupil of a cat is closedby 2 verticalbands of muscle that crosseach other aboveand belowthe pupil, as well as by a sphincter.This arrange- ment allowsa greater reduction in pupil size than is possiblewith a sphincteralone. Greaterreduction would be especiallyimportant if the maximumpupillary opening were relativelylarge as an adaptationfor night vision.For the Black Skimmerit has neither been demonstratedthat the maximumpupillary opening is greaterwith respectto the diameterof the eye than it is in related species,nor that the slit pupil effectsa greater reduction in area than is achievedby a circular pupil. To answerthese questions,we photographedthe eyesof live Black Skimmersand a Common Tern (Sternahirundo) under different light conditions.We capturedbirds in mist netson AssateagueIsland, Maryland (July 1965) and held them for 6 h to obtaina seriesof photographsof each individual.Photographs were taken with a Startekflash camera and intensitiesof light weremeasured with a light meter.The brightestlight wasmeasured under clearsky with the bird'spupil facingthe sun,and the darkestwas at night with no moon.We obtained data on one adult and onejuvenile skimmerand an adult tern. In addition we measured the length,height, and depthof the eyeballand the internaldiameter of the scleroticring of spirit specimensof a female Black Skimmerand a CommonTern in the Smithsonian Institution. Eye and pupillaryopenings drawn from projectedtransparencies are illustratedin Fig. 1. Light intensitiesfor eachcolumn are the sameand they increasefrom left to right. The seriesfor adult tern andjuvenile skimmer are incompletebecause the pupil in some photographswas not clearenough to permit an accuratedrawing. Note that thejuvenile 340] GeneralNotes J.Field Ornithol. Autumn 1981 skimmer(nearly fledged) had not yet fully developedthe capacityto producea slit pupil. Wetmore'sdescription of a "fully opened"pupil, citedabove, applies to low light condi- tions(col. 2) but not to almostcomplete darkness (col. 1). Reductionin the heightof the closedpupil to abouthalf its heightwhen fully openedsuggests that a sphincteris part of the iris musculature in the skimmer. Measurementsof the maximumand minimumpupillary openings based on the draw- ings in Fig. 1 showthat the closedpupil of the adult skimmeris only 5% of the area of the fully openedpupil, whereas that of the tern is about20%, and of thejuvenile skimmer about 10%. There was somevariation in pupillary opening of the sameindividual in consecutivephotographs as indicated by the dottedand solidoutlines in B 1. The smaller openingis not a residualreaction to a previousflash because the pupil waslargest in the secondof 3 flashpictures of the sameeye takenat aboutone minuteintervals at night. In the adult skimmer,the area of the closedpupil is about 10% of the area of the smaller openingin B 1. We are not certainthat the pupilsof the tern andjuvenile skimmerwere fully openedin our singlepictures in column 1, but our measurementsof scleroticring openings(57% of eyediameter in an adult skimmer,and 46% in a tern) suggestthat the adult skimmerhas a pupil that is relativelylarger than that of a tern. It is interestingthat the externaldimensions of the eyeballof the femaleskimmer were slightlyless than those of the much smaller tern. In answerto the questionsposed above, we found that (1) the Black Skimmer has a relativelylarger maximum pupil size than that of a Common Tern, and (2) the adult skimmereffects a greater reductionin its pupillaryarea from darknessto bright light than does the tern. These features of the adult skimmer'seye may serve to enhance nocturnalvision in supportof the bird'shabit of feedingduring eventhe darkestnights, and to protectthe retinaduring daylight feeding and otheractivities in brilliantlight. The relativelysmall eye of the skimmermay relate to its essentiallytactile foraging method in which,unlike the tern, the skimmerrarely uses its eyes to locateindividual prey.--RIc•ARD L. Zu$I AND DAVID BRIDGE,National Museumof Natural History,Smithsonian Institution, Washington,D.C. 20560. Received8 Dec. 1980; accepted21 July 1981.

Record of Movementof a LaughingGull to Hawaii from New Jersey.-•The Laugh- ing Gull (Larus atricilla) has rarely been observedas an accidentalmigrant in the Hawaiian Islands. King (Seabirds of the Tropical Pacific Ocean, Smithsonian Institution,Washington, D.C., 1967) reportedthe speciesat sea,south of the Hawaiian Islands.Berger (Hawaiian Birdlife, Univ. Hawaii Press,Honolulu, 1972) recordedthe collectionof a specimenon Oahu by EugeneKridler on 26 July 1968.During 1979 and 1980 however,several probable Laughing Gull sightingswere made by variousobservers in Hawaii. One sightingof an immaturebird, possiblya LaughingGull or a Franklin's Gull (Laruspipixcan) was reported on the Puu O Kali, Maui 1979 ChristmasBird Count by Kepler and Kepler (Elepaio40(10):139-141, 1980). On 14 December1979, an immatureLaughing Gull_ was turned in by an unknown individualat a bird salvagestation set up by the Hawaii Divisionof Forestryand Wildlife at Lihue, Kauai. The salvagestation, one of 9 set up around the Island, servesas a collectionpoint for hundredsof Newell'sShearwaters (Puffinus puffinus newelli) that injure themselvesby flying into utility wires at night on Kauai'sbrightly lit highwaysand urban areas.Citizens cooperate annually by pickingup fallen birdsand turning them in at salvagestations. Several other injured bird speciesare turned in incidentallyalong with the shearwaters.The cooperatingpublic reports the dateand locationof eachbird picked up. The LaughingGull turned in on 14 December1979 wasoriginally found near Ahu- kini, Kauai. It wasemaciated and died shortlyafter being brought to the salvagestation. Of interestwas the fact that the LaughingGull was banded (USFWS 815-58831). Sinceit wasan immaturebird, there wasa questionas to whetherit wasa LaughingGull or a Franklin'sGull. A band recoveryreport wassubmitted to the Bird BandingLabo- ratoryand it waslearned that the gull wasL. atricilla.It wasbanded as a flightlessjuvenile on 19July 1979 nearBarnegat Light, NewJersey, by Joanna Burger and Shisler. The LaughingGull reportedhere wasnot only remarkablebecause of the abnormal eastto west movement(approximately 8000 km), but alsobecause the movementtook