PROLONGED PARENTAL CARE IN ROYAL TERNS AND OTHER BIRDS N. PHILIP ASH•OLE ^ND HU•BERTO TOV^R S. DURING the last thirty years ornithologistshave accumulateda vast body of quantitativeinformation on many aspectsof the breedingbiology of a large variety of bird species,but adequateinformation on the weeks followingdeparture of the young birds from the nest is available for only a handful of species.As this period includesthe critical time when the young becomeindependent of their parents--and one when they suffer heavy mortality--the seriousnessof this gap in present knowledgeis ob- vious. The gap exists becauseof the difficulties of obtaining data after young birds have left the nest. For most speciesintensive efforts are necessaryto overcomethese difficulties. Our interest in the postfledging period was stimulated by a chanceobservation that led us to considerthe selectivepressures determining the length of the period of dependenceof young birds. OBSERVATIONS We watchedgroups of Royal Terns (Thalasseusmaximus) and Elegant Terns (Thalasseuselegans) at Laguna Grande, Departamento de Ica, Peru, on severaloccasions between early December 1966 and early Janu- ary 1967. The Elegant Tern winters in considerablenumbers on the Peru- vian coast, but the Royal Tern is seen less often. However, a group of Royal Terns is regularly presentduring the northern winter, and odd birds stay during the northern summerat Laguna Grande, which at 14ø S may be the southernmostwintering station for the specieson the west coast of SouthAmerica (cf. Koepcke,1964). At the time of our visitson 5, 6, and 10 December 1966 more than 1,000 Elegant Terns and at least 100 Royal Terns were present at Laguna Grande; on 11 January 1967 about 300 Royal Terns were present. Most of the Royal Terns were adults in the middle of the annual molt of their remiges,but perhapsone tenth were first winter birds (i.e., about 6 monthsold), distinguishablein flight by their worn, and thereforeblack- ish, primaries, and when perchedby the darker scapularsand inner sec- ondaries. At least four of the Royal Terns had bands, and of these one adult and one first winter bird were shot 10 December 1966 to determine their placeof origin. The adult, a female,proved to have been bandedas a juvenile by Lovett Williams near Pascagoula,Mississippi in July 1964. The young bird, also a female, was banded as a juvenile by H. T. Davis on Wainwright Island, Pamlico Sound,North Carolina, 4 July 1966, and 90 The Auk, 115: 90-100. January, 1968 1968Jan. ] AS•0LEA•ND TOVAR S.,Prolonged Parental Care 91 was thus probably a little lessthan 6 monthsold when collected. In each wing the innermosttwo juvenal primariesand the innermostfive second- aries (numbers 20 through 24) had been replaced by new feathers. No remigeswere in the processof growth, and "discontinuities"(Ashmole, 1963b) were noticeablebetween the old and new feathers; probably the molt had started in the northernhemisphere and then stoppedduring the southwardmigration. (In someyoung birds noneof the juvenal primaries had yet been replaced.) In the tail the two innermostpairs of juvenal rectriceshad been replacedand the vanesof the new third pair were just breaking their sheaths. Somegrowing body featherswere presenton the head, mantle, and dorsal surfaceof the wings. On the first day we watchedthis group of Royal Terns, we severaltimes heard individualsutter a seriesof loud calls in flight, and noted that these birds were always carrying fish. Twice we saw the fish given to anoth'er bird, but could not determinethe age of the recipient. As behavior of this kind is usedby adult Thalasseusterns during courtshipas well as when feedingyoung, it was clearly important to determinewhether we were wit- nessingpremature or residual courtshipbehavior or prolongedparental care. On 10 December we returned to the area and watched from 0545 until 0930, using a telescopeas well as binoculars,and three times saw adults give fish to young birds. Th'e first observationwas of an adult fish- ing, with a young bird flying below and behind it and persistentlyusing the squeaky begging call. Eventually the adult caught a fish and then flew somedistance away from the main group of birds, followedby the beggingjuvenile that then settled on the water. The adult flew down and gave it the fish without itself settling; we could not see whether the fish was actually passedfrom bill to bill or droppedto the youngbird from just above its head. The young bird continued begging for at least 10 minutes,partly in flight below a fishingadult (perhapsthe one that had fed it), but later also on the ground, when the begging was apparently directed towardsa flying bird or birds. A little later an adult with a fish flew in past th'e restinggroup, calling persistently.It was soonjoined by a young bird, which followedit for a minute or more as it flew away from the main group. The adult then droppedthe fish--evidently deliberatelyfor it made no effort to retrieve it as thesebirds normally do--and the young bird picked it up from the water surface. Later this juvenile was seen hunting by itself, though it was not seen to catch anything. The third observationwas of a calling adult that flew in with a fish, was joined by a young bird, and was also pursuedfor a short time by another adult. The adult with the fish and the young bird then flew out to sea, the young bird settled, and the adult hoveredand gave it the fish. The young bird in this casewas probably 92 ASH•OLEAND TOVAR S., ProlongedParental Care [ Auk [ Vol. 85 a banded individual. The sameday we watched an adult fly in with a fish and circle four times around the various groupsof perched birds, calling about every 2 secondsover a period of some 5 minutes, but it only suc- ceededin attracting the attention of a Band-tailed Gull (Larus belcheri) which pursuedit vigorously.Eventually the adult tern swallowedthe fish itself. Adults were again seen feedingyoung (by H. T. S.) at Laguna Grande on 11 January 1967. Subsequentlysmall groups of Royal Terns were watched (by H. T. S.) at Lagunilla, a bay a few miles north of Laguna Grande,on 13 March, 31 March, 7 April, and 21 April 1967, but juveniles were not heard beggingfor food, nor were adults seenfeeding them. On 13 March juveniles were seen successfullyfishing for themselves. We have describedour observationsin somedetail becausethey indicate that adult Royal Terns sometimescontinue to feed their young until they are about 7 monthsold and have been able to fly for more than 5 months. Althoughwe have no proof that the adults feed only their own young,the persistentcalling by both adults and young strongly suggeststhat indi- vidual recognitionis involved. Adult feedingof youngafter fledginghas previouslybeen reportedin at least two other membersof the genusThalasseus. After observingElegant Terns in San Diego Bay, California during the summerand fall seasonsof 1953, 1954, and 1955, Monroe (1956) says "Iramatures continuebegging for food, and have beennoted doing so into late November. Beggingis accomplishedexactly as in the Royal Tern. The immaturebird, upon ar- rival of an adult with food, lowers its head, thereby erecting the crest feathers,chases the adult with head low and slightlyuptilted, and peeps continuouslyuntil fed." As only small numbersof Elegant Terns were presentin San Diego Bay later than October (the area being visited by the speciesmainly in the late summerand early fall) the fact that Monroe did not recordbegging later may merely reflect the absenceof birds. How- ever we did not observeany beggingamong the wintering Elegant Terns in Peru in Decemberor any birds arriving at the resting area carrying fish. In contrastthe feedingbehavior by Royal Terns was conspicuous,despite the smaller numbersof this species. Adult Elegant Terns feedingyoung in California were also observedby Pyle and Small (1951) in August 1951. Among other membersof the genus,we are aware of relevantdata only for the SandwichTern (Thalas- seussandvicensis); Tinbergen (1953: 229) watchedadults feedingchicks during migrationin August,and David Lack (pers. comm.) saw adults of this speciesfeeding young in Norfolk, England,at least20 milesfrom their breedingcolony. Similar behavior certainly occursin a number of other ternsand gulls,but seemsnot to have beenstudied systematically. Palmer 1968Jan. ] AS•MOLEAND TOVAR S.,Prolonged Parental Care 93 (1941: 103) in his study of the Common Tern (Sterna hirundo) records that "As somejuvenals are still being fed by their parents during migra- tion, the beggingnote is often heard in traveling flocks. Not all juvenals do this, for someflocks, reported by variouswriters, were apparentlycom- posedentirely of young birds." Ralph W. Schreiberinformed us (orally) that he regularly observedyoung Herring Gulls (Larus argen.tatus)being fed by adults--under circumstancesstrongly suggestingthat they were the parents--4)nrubbish dumps in Maine from Augustto October; someof the gulls involvedwere banded in coloniesseveral hundred miles away. Simi- larly David Lack (pers. comm.) has observedyoung Herring Gulls re- peatedlybegging their (presumed)parents for food in Cornwall,England at the end of October. Thus evidencesuggests that parentalcare persists after departurefrom the breedingarea in a number of larids. However the feeding of young Royal Terns, apparently by their own parents, more than 5 months after fledging and after a trans-equatorialmigration of at least 3,000 miles, seemsto have no recordedparallel in other species. The closestanalogy may be with' the geesein