Scavenging behavior of the waved albatross in Galápagos : a potential problem with increasing longlining Item Type article Authors Merlen, Godfrey Download date 07/10/2021 13:56:50 Link to Item http://hdl.handle.net/1834/24374 20 NOTICIAS DE GALÁP AGOS No. 59 Vinson, S. B. 1994. Impact of the invasion of Solenopsis invicta Wiggins, 1.and D. Portero 1971. Flora of the Galápagos Islands. (Buren)onnativefood webs. In D. Williams, ed., Exotic ants: Stanford Univ. Press, Stanford, CA. 998 pp. Biology, impact, and control of introduced species, pp. 240- *Wilson, E. O. and R. W. Taylor. 1967. The ants of Polynesia 258, Westview Press, Boulder, CO. (Hyrnenoptera: Formicidae). Pacific Insects Monograph 14: *Wheeler, W.M. 1919. TheantsoftheGalápagosIslands. Prac. 1-109. Calif. Acad. Sci. Ser. 4, 2 (Pt. 2): 259-297. *Whee1er, W. M. 1924. The Formicidae of the Harrison Williams Boris Pezzatti, Via al Legh 3, 6710 Biasca, Switzerland. Galápagos Expedition. Zoologica 5: 101-122. Trimurti Irzan, Untere Zollgasse 132a, 3063 Ittigen, Swit- *Wheeler, W. M. 1933. The Templeton Crocker Expedition of zerland. Daniel Cherix, Museum of Zoology, Palais de the California Academy of Sciences 1932, No. 6. Formicidae Rumine, CP 448, 1000 Lausanne 17, Switzerland, and of the Templeton Crocker Expedition. Prac. Calif. Acad. Sci. Institute of Zoology and Animal Ecology, University of Ser. 4, 21: 57-64. Lausanne (e-mail: [email protected]). SCAVENGING BEHAVIOR OF THE WAVED ALBATROSS IN GALÁPAGOS: A POTENTIAL PROBLEM WITH INCREASING LONGLINING? By: Godfrey Merlen (reprinted from Pacific Seabirds1) In 1994, the population of waved albatross (Diomedea lent observation platform in the form of the flying bridge irrorata) was estimated at 15,000 breeding pairs (Ander- 3.5 m above sea level. son 1995a). Well over 99% of their breeding activity is During the mostIy calm weather, the distinctive white confined to Española Island in the Galá pagos Archi pelago. heads and necks of the waved albatross facilitated obser- By attaching satellite transmitters to breeding birds dur- vation on the sea. Higher winds caused the birds to soar ing the incubation period, Anderson (1995b) was able to abovethehorizon, whichaided the count in more adverse show that his sample (n=5) foraged over the continental conditions. We avoided counting birds twice by only shelf off Peru. However, the present report of a census searching ahead of the boato Whenever the boat stopped, carried out later in the same year shows that scavenging circled, or made other maneuvers, the census was ended. near the Galápagos Archipelago may also be an impor- Where large concentrations of albatross were encoun- tant part of waved albatross feeding. The proposed tered, several counts were made by independent introduction of new fishing techniques (longlining and observers. After leaving such an area, no counts were squid fishing) near the islands could result in a new con- made for half an hour. The average speed of travel was 8 servation problem in an already beleaguered archipelago. knots and all positions were plotted by GPS. An unpublished report by the author on the occur- Albatross in flight were usually alone, although a few rence and feeding activities of the waved albatross to many were often in the same area. On the water small suggested that the birds are, to a greater or lesser extent, groups (1-3) were common. scavengers when in the waters near the archipelago dur- By far the greatestconcentrations were found where ing the breeding season. An excellent opportunity to blue-footed boobies (Sula nebouxií)were or had recently further these observations on the distribution and scav- been feeding. On one occasion, 389 albatross were closely enging behavior ofwaved albatross carne when theauthor associated with several other species in a feeding frenzy. was asked by David Parer and Elizabeth Parer-Cook, of Suchactivities were frequent offshore in deep water, when the Australian Broadcasting Corporation, to accompany magnificent frigatebirds (Fregata magnificens), common them on a reconnaissance trip to the western part of the dolphins (Delphinus delphis), blue-footed boobies, masked archipelago, aboard the motoryacht Samba between 1and boobies (Sula dactylatra), waved albatross, white-vented 14 September 1995. We maintained a dawn-to-dusk sur- storm petrels (Oceanites gracilis), wedge-rumped storm vey on nine full days. On the other days, the Samba was petrels (Oceanodroma tethys), and Galápagos sea lions anchored or made short journeys. Observations were (Zalophus californianus) were present. Inshore (in shal- made on these short trips also. The survey was carried lower water or between the central islands) bottle-nose out mainly by two observers (G. Merlen and David Day), dolphins (Tursiops truncatus) may replace common dol- using 8x binoculars, but additional help was provided by phins. Feeding frenzies are associa ted wi th concentra tions the crew of the Samba, N aturalist Guide Mauricio Garcia, of fish, which include tunas, sardines, jacks and sharks and by D. Parer and E. Parer-Cook. There was an excel- (pers obs.). April1998 NOTICIAS DE GALÁP AGOS 21 bies followed overhead. Once the food was accessible to the birds, they began to dive on it. Frigatebirds, which had kept up, often at considerable height, then descended to mob the boobies, causing them to disgorge their re- cently gathered fish; if this occurred, the fish was ea ten by the frigatebirds. Albatross, which were present in these associations, also tried to take advantage of the melee by moving in and grabbing at the disgorged food. This was observed on dozens of occasions. We saw up to four al- batross around one "downed" booby. Albatross did not seem tomob the boobiesinitially, but appeared todepend on the aggression and flying ability of the frigatebirds. Storm petrels picked up whatever morsels were left over. These feeding activities were highly dynamic and moved over the ocean at speeds of up to 3-4 knots. Some lasted for hours, but many broke up after 20 minutes or so. The development of a feeding frenzy seemed a fixed Prediction of such events is extremely difficult, as the pattern. Dolphins found the food and blue-footed boo- productivity ofthe region iscontrolled by upwellings and 20 I..~~~-~!':.- -"'-.',r."-_.~~. ,/' \ "'" .. ~.,. 23 8. 8 ..' .' = Concentrated feeding activity ~ 8 ''' ~.~:~ '..-" . ,8 ... ,,' 0° ,_..8 \..~, -"o.' ., " ,--' - - - -.' .. ,, .~ , , , . <98 . : 10 "'-.. 1° S- .. ~ '. " 8- - .~.~ ~":r(,I .. ..8---. 12 53 .~--. o 15 30 I I I . 92° W Nautical Miles 91° W Floreana .. I I Figure 1. Survey route of the yacht Samba in the western part of the Galápagos Archipelago 1-14 September 1995. Locations of observations of waved albatross and of feeding concentrations are shown on survey route track. 22 NOTICIAS DE GALÁP AGOS No. 59 fronts between water masses, which are unpredictable than 5% of the boobies feeding. The figure was often as and unstable in themselves. On two consecutive days we low as 2%. found boobies and albatross in the same area to the south It is not easy to ascertain the exact relationship of the of Cape Hammond (southwest Fernandina). However, organisms involved in feeding frenzies, because, in the the great concentration along the equator was ephemeral Galápagos, common dolphins are verynervous ofthe close and not repeated over three further days of observation. approach of vessels. This may be due to the presence of Perhaps it was due to changes in oceanic conditions or purse seine tuna boats, which often set their nets on the perhaps it was because on the first day (7th September) dolphins, because tunas associate with them. Or perhaps we witnessed an attack (O°09.4'N 9P44.0'W) by 7 orcas any strange noise alarms them since their predator, the (Orcinus arca) on the feeding common dolphins. They orca, is present year round. killed at least one dolphin, and the small pieces that re- It seems that the waved albatross is, at least at some mained were scavenged by storm petrels, frigatebirds and times, a scavenger. From the duration of the observations albatross. Albatross also scavenged a large dead squid and their limitation to daylight, it is not possible to say (O°19.9'S 91°43.4'W), later identified as Angistrocheirus how important this method of feeding is, nor is it possible lesevri. Large concentrations of albatross were always to state the importance of feeding frenzies, even though associated with feeding frenzies. this feeding technique is extremely common. Should it be During the 24 days of observations (the cumulative important, then the availability of food to scavenge has to time of the two reports), not a single albatross was seen be maintained. This, in turn, means that the structure of feeding on live prey. Harris (1973) reported that the main feeding frenzies and the well being of all their compo- food of breeding waved albatross was fish and squid. nents (fish, dolphins, boobies, frigatebirds) may be of Since blue-footed boobies do not eat squid, the albatross importance to the feeding, and, ultimately, to the breed- must gather this themselves or gather it from other birds ing success of waved albatross. In this uncertain situation, that frigatebirds attack such as swallow-tailed gulls it is vital to maintain the viability of this pelagic trophic (Creagrus furcatus). Some of the fish (Clupeids) found in system that is found in the western part of the Galápagos albatross stomach contents in Harris's study could have Archipelago. been scavenged. Harris (1973) observed the interaction of One of the reasons that the marine environment has albatross with boobies and felt that this behavior did not remained relatively untouched until the last few years is contribute greatIy to their diet. However, the frequency that the fishing fleet has been slow, local, and primitive in with which we observed this albatross behavior leads me the techniques used.