October 1982] Short Communications 781 GARRETT,K., & J. Du•. 1981. Birds of southern ArcticOcean in 1881.Washington, Government California. Los Angeles, Los AngelesAudubon Printing Off. Soc. --. 1887. Report upon natural history collections HARTERT, E. 1920. The birds of the Commander made in Alaskabetween the years1877 and 1881. Islands. Novitates Zool. 27: 128-158. U.S. Army, SignalServ. Arctic Ser. Publ. 3. JEHL,D. R., & J. R. JEHL,JR. 1981. A North American RIOGWAY, R. 1919. The birds of Middle and North record of the Asiatic Marbled Murrelet (Brachy- America, part 8. U.S. Natl. Mus. Bull. No. 50. rhamphusmarmoratus perdix). Amer. Birds 35: SEArX,S.G. 1974. Breedingphenology and clutch 911-912. size in the Marbled Murrelet. Auk 91: 10-23. KESSEL,B., & D. D. GIBSON. 1978. Status and dis- 1975. Aspects of the breeding biology of tribution of Alaska birds. Studies Avian Biol. the Marbled Murrelet in British Columbia. Bird- No. 1. Banding 46: 141--154. KOZLOVA, E. V. 1957. Charadriiformes, suborder SIMO•S,T.R. 1980. Discoveryof a ground-nesting Alcae. Fauna of USSR: Birds 2(3): 1-140 (R. Et- Marbled Murrelet. Condor 82: 1-9. tinger, transl.).Jerusalem, Israel Program for Sci. STEINEGER, L. 1886. On Brachyramphusperdix (Pall.) Transl. and its nearest allies. Zeitschrift Gesammte Or- KuzYA•CI•,A. P. 1963. On the biologyof the Long- nithol. 3: 210-219. billed (Marbled) Murrelet. Ornitologiya 6: 315- TACZA•OWS•CI,L. 1893. Fauna Ornithologiquede la 320. Siberie Orientale. Mem. Acad. Imp. Sci. St. Pe- LEwts,H.F. 1924. Occurrenceof Synthliboramphus tersbourg39: 685-1278. antiquusin the Province of Quebec. Can. Field- UOVARVX,M.D. F. 1963. Zoogeographicalstudy Natur. 37: 118-119. of the Pacific Alcidae. Pp. 85-111 in Pacific MURIE, O. J. 1959. Fauna of the Aleutian Islands basin biogeography(J. L. Gressitt,Ed.). Hono- and Alaska Peninsula. U.S. Dept. Interior, Fish. lulu, Bishop Museum Press. Wildl. Serv., North Amer. Fauna, No. 61. VAURI•, C. 1959. Birds of the Palearctic fauna. Lon- N•rso•, E. W. 1883. Birds of Bering Sea and the don, H.F. and G. Witherby Ltd. Arctic Ocean. Pp. 57-l•8 in Cruise of the Rev- enue-Steamer Corwin in Alaska and the N.W. Received9 November1981, accepted12 March 1982. BreedingOspreys Feed FledglingsThat Are Not Their Own ALAN POOLE BostonUniversity Marine Program, Marine Biological Laboratory, Woods Hole, Massachusetts02543 USA Many speciesof birds are known to have "helpers ers(Fernandez and Fernandez 1977, Judge 1981) have at the nest," i.e. individuals that do not breed but also notedoccasional nest-switching by fledgling insteadhelp others (often kin) tend young (Brown Ospreys,no one has describedthis behavior in detail 1978,Emlen 1978).Examples of breedingbirds that or consideredit in an evolutionarycontext. similarlyaccept parental duties for nonoffspringare The Ospreysunder study were part of a population far rarer, however.Where one memberof a nesting of 19 activepairs that nestedin the WestportRiver pair has been experimentallyremoved, replacement estuaries of southeastern coastal Massachusetts in mates (consorts)rarely feed young (Power 1981). 1980. All five nests observed were located on 4-7-m- Amongnidicolous communal nesters like the Groove- high artificialplatforms in open saltmarsh habitat, billed Ani (Crotophagasulcirostris) and the Mexican and all were within sightof at leasttwo other nests. Jay (Aphelocomaultramarina), several females will Usinga 15•0 x telescope,I identified fledged young sharein the feedingof young not necessarilytheirs by numberedplastic leg bands. Adults were simi- (Veherencamp1977, Brown 1972), but, amongspecies larly markedand/or were identifiedby their fidelity that do not share nests, such natural "adoption," to a particular nest site. At a distance, adults were necessarilyconfined to mobilefledglings, seldom oc- distinguishedfrom fledglingsby plumage.Obser- curs. Bitterbaum and Brown (1981)report that Purple vationsspanned the period 16-23 July1980 and av- Martins (Prognesubis) with young of their own will eraged3 h per day. Most youngWestport Ospreys feed other fledglingsthat intrude into their nests. fledgeabout mid-July; Ospreys are fully fledgedat Here, I reportobservations of nestingOspreys (Pan- about 50 days of age (Stinson1977). dionhaliaetus) likewise adopting and providingfood I first observednest-switching among Westport for fledglingsfrom nearbynests. While other work- Osprey fledglingson 16 July 1980, when nest H1, 782 Short Communications [Auk, Vol. 99 whereonly one young(Jll) had beenpresent pre- preyfamily unitsremain intact for 12-50days after viously,contained two young.The H1 femalefed fledgingoccurs; he recordedno nestshifts at 11 nests bothyoung on fish,which the male had delivered to watchedduring this period. Judge(1981), however, the nest.The intruder fledgling(F81) was from HCT did note two brief nest shiftsby Ospreyfledglings, nest, 150 m distant from H1, and was the smallestof and intruding young were fed in both cases.Fer- thethree young that had been in HCT before16 July. nandezand Fernandez(1977) saw one nestlingswitch F81 was about52 daysold on 16 July,while Jll was nestson two separateoccasions, but they did not only 44 daysold and couldnot fly. report any feeding of this young. Theseobserva- On 17 July,I again saw fledglingF81 at nestH1; tions, togetherwith my own, suggestthat Osprey the femalefed bothyoung on two differentfish de- familiescan be considerablymore fluid afterfledging liveries. The female did not appearto discriminate than Stinson's(1977) study indicated. betweenyoung, as both were fed roughlyequal Why might suchnest-switching occur? It is easy amounts.On 19 Julyat 0610I saw F81 feed itself at to seethat subordinatefledglings from large broods nest H1 while Jll rested beside it. When F81 had couldimprove their foodintake and thustheir prob- slowedin its feeding,Jll approachedF81, took the abilityof survivalif theycould become the dominant remainingfish from it, and beganto feed. During fledglingat a nestwith youngerbirds. Both vagrant this entirefeeding the adultfemale remained perched young (F81 and F87) identifiedin this study came at the nestedge while the male perchedbelow the fromlarge broods where they were the smallest(and nest;neither interfered in any way with the feeding presumablythe subordinate)young, and both were young. At 0650F81, disturbedby a passingcanoe, substantiallyolder and betterat flyingthan acquired flew to nest H2, 100 m from HI; H2 contained three nestmates. In addition,all intruderfledglings moved youngat this time. The H2 female,perched below to nestswithin sight of their natal nest, suggesting the nest, made no attempt to drive away F81 as it that proximitywas also a factorin thisbehavior, per- flew in. At 0707, the H2 male delivered a fish to its haps becauseof the stimulusof neighboringfood nest,and oneyoung (not F81)began to feed itself. deliveriesthat could be easily seen. At 0900 F81, which had not fed at H2, flew back to While it is not difficultto understandwhy sub- H1, evoking no responsefrom the HI adults, al- ordinate Osprey fledglings might benefit from thoughthey did chasean intrudingadult, which had switchingnests, it is harderto explainwhy breeding followed F81 toward the nest. F81 remained in the adultsthat tolerateand feedstrange young would not vicinityof nestsH1 andH2 untilthe watch ended at be selectedagainst. Vagrant young could reduce the 1000.F81 was also seen perched and feedingsporad- food availableto a pair's own fledglings,thus poten- icallyat H1 on both 17 and 18July, but it was never tially loweringthat pair'sfitness. If parasiticyoung observedback at its natal nest, HCT, after first being are detrimental to parental fitness, adult Ospreys seen at HI. should be able to distinguishyoung, as many colo- At nest SGI, containingthree young, a fourth nial birds are capable of doing (Beer 1971). Stinson fledgling(F87 hatched in nestSS 90 m away) was (1976)suggests that Ospreysdo have the ability to presenton 22July and was seen to begfrom the adult recognizeoffspring, but the evidencehe cites(par- SGI male, which had no food. F87, the smallestSS entsreturning to a fledglingthat had beenremoved chick,was 5-9 daysolder than the youngin the SGI from a nestsite for severaldays and then put back) nest.On 23 JulyI saw F87 at anothernest (PI, 20 m couldjust as well indicatenest-site fidelity as rec- from SGI), where it fed itself for 10 min on food ognitionof offspring.Ospreys do appearcapable of deliveredby the PI male after two of the three PI makingfine visualdistinctions, however: they tol- younghad fed on thesame prey. F87 did notappear erate matesbut not other adults that approachtheir at its natal nest on either 22 or 23 July. nests,and they distinguishthe "familiar"boat of a A final exampledemonstrates how fluid these researcherfrom other boats, defendingnests at a far fledglingassemblages at Osprey nests can be. At nest greaterdistance against the formerthan the latter RH (3 youngprefledging), 5 youngwere presenton (Stinson1976; pers. obs.). Judge (1981) suggested that, 23 Julyat 1545;at 1620only 1 fledglingwas still at althoughadult Ospreysmay recognizeindividual the nest,and 2 otherswere perchedin a nearbytree young,they feed immatureson the nestregardless (the other 2 had disappeared).At 16402 young were of relationship. Thus, it seemslikely that Ospreys in the RH nest, 2 were in the tree, and 1 had dis- are ableto tell fledglingsapart, but convincingdata appeared;at 1915,1 youngwas in the nest,2 were on this questionare still needed. in the tree, and