Sterna Hirundo)
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Vol. 1931XLVIII1 j JACKSONANDALLAN, C0•/gat/• ofTer•. 17 EXPERIMENT IN THE KECOLONIZATION OF THE COMMON TERN • (STERNA HIRUNDO). BY C. F. JACKSON AND PHILIP F. ALLAN. DURINGthe summerof 1929an attemptwas made at the Marine ZoologicalLaboratory at the Islesof Shoalsto establisha colony of Terns (Sternahitundo) on North Head of AppledoreIsland. This colonization was tried because of the threatened destruction of the colonyon Londoner'sIsland. The first recordsof a colonyof thesebirds at the Shoalscome from two of the oldest inhabitants. "Uncle" Oscar Leighton, ninety-oneyears of age, recalls a colony on Duck Island where thousandsof "mackerelgulls" nestedyearly. In his boyhood the fishermenused to collectthe eggsfor food,and the men and youthsshot the adults for the feathers. This colonypersisted until 1898 when "Captain" Caswellmoved to Duck Island. As a resultof this disturbance,the colonymigrated "down the Maine Coast" and settledon variousislands. In 1922a few pairsstarted nestingon Londoner'sIsland. This new colonyincreased rapidly and duringthe summerof 1928approximately one thousandpairs were breeding on the island. The year after the establishmentof the colony,a cottagewas erectedon the'island. The cottage,however, was not occupied to any extent until the summerof 1927. At this time the island wassold and the newowner, not desiringthe presenceof the birds, set aboutto drive them from the island. The eggswere destroyed, the youngwere killed, and the adultskept in a state of constant confusion. During the summerof 1929 large numbersof eggs were broken,and numerousyoung were killed. A dog was kept rovingthe islandand nosedout and killed many of the fledglings, and a flockof hensdestroyed great numbers of eggs. Althoughthe situationwas unfortunate, the ownerwas evidently well within his rightsin destroyingthe birdson his own property. In view of the above circumstances it was decided that an at- tempt at recolonizationmight be the meansof savingthe colony. x Contribution No. 6•Zoological Laboratory, University of New Hampshire, Durhgm• New Hampshire. C.F. Jackson, Director. 18 JACKSONAN•ALLAN, Colonization ofTerns. [J•n.Auk 'Aside from the barest possibilityof success,the project afforded an excellent opportunity for observingthe habits of the bird as well as its adaptability. It wasfully realizedthat suchan experi- ment would causea high mortality, but on the other hand, the mortalitywould be just as high if the youngbirds were left in the original colony. Londoner's Island is at the south-western corner of the Isles of Shoalsgroup. It is a ruggedmass of rock of about fifteen acres. The majority of nestswere on the higherportions which rise about forty feet above the high-tide mark. The nestswere most plentiful duringJune. They usuallycon- tained two or three eggs,occasionally four. The eggswere some- times laid on the bare rock, but were usually in shallow nests scoopedin the soil among the bushes. Some of the nests were built up of rock-weedto a heightof two or three inches. It may be noted here that about ten pairs of the rarer Roseate Terns (8terna clougalli)nested in the deeperbrush of the northern end. A few of the youngof this specieswere involved in the experiment. In choosinga location for the experimentthe environmental factors of Londoner's Island were carefully considered. North Head on AppledoreIsland was finally chosenas an ideal placefor the experiment. Here an area approximatelyequal to that of Londoner'sIsland was available. The vegetationof this location is practically the same as that on Londoner's. The altitude and rocky shore-lineare similar. The water is deep, and small fish are plentiful. Justoff-shore there is a largerock whichrises about twentyfeet abovethe high-tidemark. HereTerm commonlyalight. Betweenthis projectionand the shoreis a largepool which is fairly shallow. This regionis aboutone and onehalf milesfrom the presentcol- ony, and is on one of the main tracksof flight to and from the reg- ular fishinggrounds of the birds. Normally there are a number of Terns fishing along this shore,and in the deepfjord-like cut at the northernextremity of the area. About a mile to the north-east is a large colonyof Herring Gulls (Larus argentatus). The prox- imity of this colonyappeared to be the only disadvantageof the proposednew colonyof Terns. There wasthe possibilitythat the Gulls might kill the young Terns, or that the adults might not VoL 1931XL¾III] j JACKSONANDALLAN, Colonization ofTerns. 19 settle so near the Gull colony. However, the other advantages of North Head more than offset this feature. At the time the experimentwas started,it was already late in June. Large numbersof the youngwere hatched, and a few were well grown. Arrangementswere made for caringfor about three hundredyoung• A pen of matchedboards was constructed,12 • by 12• by 10" in height. The top was left opento allow the old birds free accessto the young. Eight membersof the University of New HampshireMarine ZoologicalLaboratory collected the young. Each memberof the party took a lane about six feet wide and collectedall of the young birdsin this area. It is the habit of the youngTern to creepunder rocks, bushes,and grassto hide from the rays of the sun. This, added to the difficultiesof wading throughpoison ivy, the swoop- ings of the distraughtparents, and the stable-flieswhich appear indispensableto a sea-bird colony, made the work laborious. The young birds were put in bushel basketsand immediately transportedto Appledore,and placedin the pen. After the young were in the pen five adults flew back and forth over it until dark. They calledconstantly, and the youngset up an answeringclamor. Severalcunners (Tautogolabrua adspersua) were choppedfinely with an ax, and fed to the young birds. Force feedingwas nec- essaryin most cases. A number of bushelbaskets were left for cover,and brushwas distributedaround the pen. The birdswere then left for the day to allow the old birds,who were apparently very curiousabout the whole proceeding,to becomeused to the new situation. At nightfall the very youngestchicks were put in covered baskets. .. The followingday there were twelve adultspresent throughout the whole day. The youngwere fed two mealsof choppedfish. Severaladults broughtfish, and one or two lit on the edgeof the penfor a few seconds,but nonewere seen to'feed the chicks. Fresh water was left in fiat dishesin various parts of the pen and the chicksdrank and bathed freely. From the third day on the fish was ground whole in a meat-grinder. The chicks acceptedit much more readily in this form. Several of the medium grown chickspicked up the fish from a tray in which the residueof the food was placed. The heaviest.mortalitywas among the oldest 20 JACKSO•Am) ALL•, ColonizationofTerns. [Auk[Jan. and the youngest birds. The former were shy and could not be made to eat, while the latter were so numerousthat they could not receive enoughindividual attention. At the end of the third day eighty had died. About forty adults were near the new col~ ony most of the time now. The mortalityrate dropped,and after the firstweek but fewof the young birds died. By the end of this time the adults were feeding an amount equal to possiblyone-third of that which was put in the pen in the form of ground fish. Often there were one hundred and fifty adults flying about the vicinity. All of the young ate from the tray, and came running like so many chickens at the sight of food, and a number had started to fly. Toward the latter part of July all of the remaining young were flying, and it was thought desirableto obtain more. Only seventy- eight were collected on this trip, as only the medium sized ones were taken. The care of thesewas the sameas of the preceding group. Once or twice they were left for a day without food in order to cheek on the amount of food brought by the adults, but they never seemedparticularly hungry the following day. Many of the young flew continuallyin and out of the pen, but cameback. whenever food was brought. The adults seemedfewer as the number of the youngdecreased. The young birdsspread all along the shore during the day, and returned to the pen at night. One interestingfeature of the behaviorof the adults was the way in which they drove the young up from the tide region at night. After sitting amicably with the young on the rocks they would suddenlyrise and noisily swoop at the youngsters,driving them toward the pen. Someof the young were surprisinglytame, and would light near any spot where fish was being ground. They would beg for piecesby calling and fluttering the wings as they did when the adults brought food. The bright-eyed little fellows watched every movement, and open-billed,tried to catch chunks of fish liver tossedto them. One flew half a mile to a place where fish were being cleaned,and was fed upon the scraps. He was easily picked up. By the end of the first week in Augustthe feedingwas discon- tinued as all of the birds collected were now able to care for them- selves. It is estimatedthat about eighty birds were reared to this Vol. 1931XLVIII] J J.•eKSON.•N•)A•I•,•, Colonization ofTerns. 21 stageof maturity. A visit to the colonythe last weekin August showedthat a numberof the youngwere remaining in the vicinity. A pair of adults accompaniedeach bird and all were engagedin fishing. Often a youngstercoming in from the sea alightedon the familiar rocks. Theresults of thisexperiment were awaited with a greatdeal of interest. On a trip to the islandssoon after the Terns appeared in 1930 many pair were seen in the vicinity of North Head on AppledoreIsland. It was not possibleto again visit the islands until the middle of June when it was definitely establishedthat a sizablecolony was nesting on North Head. A carefulsearch about June 18 showedthirty nestswith from two to three eggs.