FORAGING DYNAMICS OF SEABIRDS IN THE EASTERN TROPICAL PACIFIC OCEAN Larry B Spear, David G Ainley, and William A Walker Studies in Avian Biology No 35 A PUBLICATION OF THE COOPER ORNITHOLOGICAL SOCIETY Front cover photograph of Great Frigatebird (Fregata minor) by R L Pitman Rear cover photograph of Red-footed Booby (Sula sula) with flying fish by R L Pitman STUDIES IN AVIAN BIOLOGY Edited by Carl D Marti 1310 East Jefferson Street Boise, ID 83712 Spanish translation by Cecilia Valencia Studies in Avian Biology is a series of works too long for The Condor, published at irregular intervals by the Cooper Ornithological Society Manuscripts for consideration should be submitted to the editor Style and format should follow those of previous issues Price $15.00 including postage and handling All orders cash in advance; make checks payable to Cooper Ornithological Society Send orders to Cooper Ornithological Society, % Western Foundation of Vertebrate Zoology, 439 Calle San Pablo, Camarillo, CA 93010 Permission to Copy The Cooper Ornithological Society hereby grants permission to copy chapters (in whole or in part) appearing in Studies in Avian Biology for personal use, or educational use within one’s home institution, without payment, provided that the copied material bears the statement “©2007 The Cooper Ornithological Society” and the full citation, including names of all authors Authors may post copies of their chapters on their personal or institutional website, except that whole issues of Studies in Avian Biology may not be posted on websites Any use not specifically granted here, and any use of Studies in Avian Biology articles or portions thereof for advertising, republication, or commercial uses, requires prior consent from the editor ISBN: 978-0-943610-79-5 Library of Congress Control Number: 2007930306 Printed at Cadmus Professional Communications, Ephrata, Pennsylvania 17522 Issued: 2007 July 11 Copyright © by the Cooper Ornithological Society 2007 CONTENTS AUTHOR ADDRESSES x ABSTRACT INTRODUCTION METHODS DATA COLLECTION Specimens Stomach processing and prey identification Feeding behavior DATA ANALYSIS Comparison of diets Analysis of temporal, spatial, and demographic factors 11 Multiple regression analyses 12 Diet diversity 12 Prey size 12 Scavenging 13 Stomach fullness 13 Timing of feeding 14 Mass of prey consumed in relation to foraging strategy 14 Calculation of consumption rate for different prey groups 14 Estimation of total prey mass consumed 15 Statistical conventions 16 RESULTS 16 COMPARISON OF SEABIRD DIETS 16 TEMPORAL AND SPATIAL ASPECTS OF DIET 20 DIET DIVERSITY 21 PREY SIZE 22 SCAVENGING 27 STOMACH FULLNESS 29 TIMING OF FEEDING 32 FLOCK COMPOSITION AND PREY AMONG BIRDS FEEDING OVER TUNA 35 SUMMARY OF DIET COMPOSITION 35 PROPORTION OF PREY OBTAINED USING THE FOUR FEEDING STRATEGIES 36 SIZE OF THE SEABIRD AVIFAUNA AND TOTAL PREY MASS OBTAINED ACCORDING TO FEEDING STRATEGY 36 DISCUSSION 41 SEABIRD DIETS 42 Pelecaniformes 42 Large Procellariiformes 43 Small Procellariiformes 43 Laridae 43 DIET PARTITIONING 44 DIET VARIATION WITH RESPECT TO ENVIRONMENTAL FACTORS 44 RELIANCE OF ETP SEABIRDS ON LARGE PREDATORY FISH 45 NOCTURNAL FEEDING 45 SCAVENGING 47 DIURNAL FEEDING ON NON-CEPHALOPOD INVERTEBRATES 47 SUMMARY OF USE OF THE FOUR FEEDING STRATEGIES 47 FLOCK VERSUS SOLITARY FORAGING 48 SPECIES ABUNDANCE IN RELATION TO DIET 48 COMPARISON WITH A POLAR MARINE AVIFAUNA 48 THE IMPORTANCE OF TUNA TO TROPICAL SEABIRDS 49 ACKNOWLEDGMENTS 50 LITERATURE CITED 50 TABLES TABLE SAMPLE SIZES, BY SEASON AND YEAR, OF SEABIRDS COLLECTED IN THE ETP AND THAT CONTAINED PREY TABLE BIRDS COLLECTED IN ASSOCIATION WITH YELLOWFIN AND SKIPJACK TUNAS TABLE COLLECTION DETAILS FOR THE 30 MOST-ABUNDANT AVIAN SPECIES IN THE ETP TABLE FLOCK INDEX, PRIMARY FEEDING METHOD, MEAN MASS (G ± SD), AND PREY-DIVERSITY INDEX (H’) FOR THE 30 MOST ABUNDANT AVIAN SPECIES OF THE ETP 10 TABLE SEASON AND YEAR OF THE OCCURRENCES OF EL NIÑO, NEUTRAL, AND LA NIÑA PHASES OF THE EL NIÑO SOUTHERN OSCILLATION 12 TABLE PRINCIPAL COMPONENT ANALYSES BY EIGHT GROUPS OF PREY IN THE DIETS OF ETP SEABIRDS 17 TABLE PRINCIPAL COMPONENT ANALYSES FOR TEMPORAL/SPATIAL COMPARISONS BY EIGHT GROUPS OF PREY IN THE DIETS OF 10 ETP SEABIRDS 22 TABLE REGRESSION ANALYSES FOR THE RELATIONSHIP BETWEEN PREY SIZE AND VAROIUS INDEPENDENT VARIABLES 27 TABLE STANDARD LENGTHS OF PHOTICHTHYIDS AND MYCTOPHIDS EATEN BY CERTAIN ETP SEABIRDS 27 TABLE 10 REGRESSION ANALYSES FOR THE RELATIONSHIP BETWEEN PREY SIZE AND VARIOUS INDEPENDENT VARIABLES 29 TABLE 11 MEAN (± SD) FOR STANDARD LENGTHS OF THE MORE ABUNDANT PREY CONSUMED BY CERTAIN ETP SEABIRDS THAT FEED IN MULTISPECIES FLOCKS 30 TABLE 12 MEAN LOWER ROSTRAL LENGTHS (MILLIMETERS) OF CEPHALOPOD BEAKS EATEN BY ETP PROCELLARIIFORMS 31 TABLE 13 RESULTS OF REGRESSION ANALYSES FOR THE RELATIONSHIP BETWEEN STOMACH FULLNESS AND CERTAIN INDEPENDENT VARIABLES 32 TABLE 14 COMPOSITION OF WHOLE PREY FOUND IN THE STOMACHS OF SEABIRDS COLLECTED WHILE FEEDING IN FLOCKS INDUCED BY YELLOWFIN AND SKIPJACK TUNA 35 TABLE 15 SPECIES COMPOSITION OF SEABIRD FLOCKS OBSERVED WHILE FEEDING IN FLOCKS INDUCED BY YELLOWFIN AND SKIPJACK TUNA 37 TABLE 16 PERCENT OF FISHES, CEPHALOPODS, AND NON-CEPHALOPOD INVERTEBRATES IN THE DIETS OF THE 30 MOST-ABUNDANT ETP SEABIRDS 38 TABLE 17 AVERAGE PREY MASS IN GRAMS (MEAN ± SE) OBTAINED BY ETP SEABIRDS WHEN USING EACH OF FOUR FEEDING STRATEGIES DURING A GIVEN 24-HR PERIOD 39 TABLE 18 ESTIMATE OF THE TOTAL PREY MASS CONSUMED BY ETP SEABIRDS USING EACH OF FOUR FEEDING STRATEGIES 40 FIGURES FIGURE The study area in the eastern tropical Pacific Ocean, including locations (shown with dots) where birds were collected The horizontal dashed line separates the Equatorial Countercurrent from the South Equatorial Current (Tropical Front); and the vertical line separates east from west as referred to in the text The staircase line effect along the coast on the east side of the study area denotes the boundary separating pelagic waters (to the west) and coastal waters to the east Shading indicates large-scale patterns of ocean productivity: the three gradations shown are, darker meaning higher values: 300 mgC m-2 d-1 (from Longhurst and Pauly 1987, p 122) FIGURE The distribution of at-sea survey effort of seabirds in the eastern Pacific Ocean (1983–1991) Each dot represents one noon ship position The staircase line effect along the coast on the east side of the study area denotes the boundary separating pelagic waters to the west and coastal waters to the east FIGURE Results of the PCA comparing diets among 30 species of seabirds from the ETP Diets of species enclosed in the same circle were not significantly different (Sidak multiple comparison tests, P > 0.05) BORF = Red-footed Booby (Sula sula), BOMA = Masked Booby (S dactylatra), BONA = Nazca Booby (S granti), FRGR = Great Frigatebird (Fregata minor), JAPA = Parasitic Jaeger (Stercorarius parasiticus), PEBU = Bulwer’s Petrel (Bulweria bulwerii), PTBW = Black-winged Petrel (Pterodroma nigripennis), PTDE = DeFilippi’s Petrel (Pterodroma defilippiana), PTHE = Herald Petrel (Pterodroma arminjoniana), PTJF = Juan Fernandez Petrel (Pterodroma externa), PTKE = Kermadec Petrel (Pterodroma neglecta), PTMU = Murphy’s Petrel (Pterodroma ultima), PTPH = Phoenix Petrel (Pterodroma alba), PTSJ = Stejneger’s Petrel (Pterodroma longirostris), PTTA = Tahiti Petrel (Pterodroma rostrata), PTWN = White-necked Petrel (Pterodroma cervicalis), PTWW = White-winged Petrel (Pterodroma leucoptera), SHCH = Christmas Shearwater (Puffinus nativitatus), SHSO = Sooty Shearwater (Puffinus griseus), SHWT = Wedge-tailed Shearwater (Puffinus pacificus), STMA = Markham’s Storm-Petrel (Oceanodroma markhami), STWR = Wedge-rumped Storm-Petrel (Oceanodroma tethys), STLE = Leach’s Storm-Petrel (Oceanodroma leucorhoa), STWB = White-bellied Storm-Petrel (Fregetta grallaria), STWF = White-faced Storm-Petrel (Pelagodroma marina), STWT = White-throated StormPetrel (Nesofregetta fuliginosa), TEGB = Gray-backed Tern (Onychoprion lunatus), TESO = Sooty Tern (Onychoprion fuscatus), TEWH = White Tern (Gygis alba), TRRT = Red-tailed Tropicbird (Phaethon rubricauda) 17 FIGURE Percent of each of eight prey groups in the diet of seven smaller species of petrels, which feed solitarily in the ETP Percent was calculated as the total number of prey representing a given prey group divided by the total number of prey summed across all eight prey groups in a given seabird species’ diet Values of N (in parentheses) are the number of birds containing at least one prey item Error bars denote the standard error See Methods for details on classification of the eight groups of prey species, and Appendices 3–9 for detailed prey lists 18 FIGURE Diet composition of the eight medium-sized petrels, most of which feed solitarily in the ETP For each seabird species, percent was calculated as the total number of prey representing a given prey group divided by the total number of prey summed across the eight prey groups in a given seabird species’ diet Values of N (in parentheses) are the number of birds containing at least one prey item Error bars denote the standard error See Methods for details on classification of the eight groups of prey species, and Appendices 10–17 for detailed prey lists and predator sample sizes 19 FIGURE Diet composition of the 15 species of birds that generally feed over surface-foraging tuna in the ETP For each seabird species, percent was calculated as the total number of prey representing a given prey group divided by the total number of prey summed across the eight prey groups in a given seabird species’ diet Values of N (in parentheses) are the number of birds containing at least one prey item Error bars denote the standard error See Methods for details on classification of the eight groups of prey species, and Appendices 18–32 for detailed prey lists and predator sample sizes 21 FIGURE Results of the PCA to compare diets between sexes for each of 10 species of seabirds in the ETP See Fig for species codes (first four letters) The fifth letter in the code designates female (F) or male (M) Diets of species enclosed in the same circle did not differ significantly between sexes (Sidak multiple comparison tests, all P > 0.05) Differences among species are not shown (see Fig for those results) 22 FIGURE Results of the PCA to compare diets between spring and autumn for each of 10 species of seabirds in the ETP See Fig for species codes (first four letters) The fifth and sixth letters in the code designate spring (SP) and autumn (AU) Diets of species enclosed in the same circle did not differ significantly between seasons (Sidak multiple comparison tests, all P > 0.05) Differences among species are not shown (see Fig for those results) 23 FIGURE Results of the PCA to compare diets of 10 species of seabirds between the South Equatorial Current and North Equatorial Countercurrent See Fig for species codes (first four letters) The fifth letter in the code designates current system; S = South Equatorial Current, or N = North Equatorial Countercurrent Diets of species enclosed in the same circle did not differ significantly between current systems (Sidak multiple comparison tests, all P > 0.05) Differences among species are not shown (see Fig for those results) 23 FIGURE 10 Percent of eight different categories of prey in the diets of different species of seabirds occurring within different current systems, longitudinal sections, or during La Niña vs El Niño See Methods for details on divisions for these waters or temporal periods For current system, longitudinal section, and ENSO phase, the light bars designate the SEC, East, and El Niño, respectively; and the dark bar designates the NECC, West, and La Niña 24 FIGURE 11 Results of the PCA to compare diets between east and west longitudinal portions of the ETP for each of 10 species of seabirds See Fig for species codes The fifth letter in the code designates east (E) or west (W) Diets of species enclosed in the same circle did not differ significantly between longitudinal sections (Sidak multiple comparison tests, all P < 0.05) Differences among species are not shown (see Fig for those results) 25 FIGURE 12 Results of the PCA to compare diets between El Niño and La Niña for each of 10 species of seabirds in the ETP See Fig for species codes The fifth letter in the code designates El Niño (E) or La Niña (L) Diets of species enclosed in the same circle did not differ significantly between the two ENSO phases (Sidak multiple comparison tests, all P < 0.05) Differences among species are not shown (see Fig for those results) 25 FIGURE 13 A) Shannon-Wiener diet-diversity indices (H’ ) for species of seabirds in the ETP having sample sizes (number of birds containing prey) ≥9 See Table for species’ sample sizes; Fig for species code definitions B) Mean H’ ± SD among six groups of ETP seabirds 26 FIGURE 14 (a) Average otolith length (millimeters) of 10 species of prey taken by five species of seabirds that feed on smaller fishes Predator species’ bars for each prey species are from left to right (in order of increasing predator mass): Wedge-rumped Storm-Petrel (Oceanodroma tethys), Leach’s Storm-Petrel (O leucorhoa), Black-winged Petrel (Pterodroma nigripennis), White-winged Petrel (P leucoptera), Tahiti Petrel (P rostrata) (b) Average otolith or beak length (millimeter) of three species of prey taken by six species of seabirds that feed on larger prey Predator species’ bars are from left to right (in order of increasing mass): Sooty Tern (Onychoprion fuscata), Wedge-tailed Shearwater (Puffinus pacificus), Juan Fernandez Petrel (Pterodroma externa), Red-tailed Tropicbird (Phaethon rubricauda), Nazca Booby (Sula granti), Masked Booby (Sula dactylatra) See Appendices for prey sample sizes 28 FIGURE 15 Stomach fullness (mean ± SE) of 29 species of seabirds in the ETP (Nazca booby [Sula granti] excluded; see Methods) Stomach fullness is the mass of food in the stomach divided by the fresh mass of the predator (minus mass of the food) multiplied by 100 See Table for approximate sample sizes Verticle line projecting from x-axis separates flock-feeding species (left side) from solitary feeding species (right side) 30 FIGURE 16 Otolith condition (mean ± SE) in relation to hour-of-day among five groups of seabirds: (a), myctophids caught by storm-petrels, (b), myctophids caught by solitary procellariids, (c), myctophids caught by flocking procellariids, (d), exocoetid-hemiramphids caught by flock-feeders; and (e), diretmids, melamphaids, and bregmacerotids caught by all procellariiforms Otolith condition represents pristine otoliths of freshly caught fish and represents highly-eroded otoliths of well-digested fish Numbers adjacent to means are otolith sample sizes, where one otolith represents one individual fish (see Methods) For myctophids, diretmids, melamphaids, and bregmacerotids, the line of best fit (solid line) was extrapolated (dashed line) to the x-axis at otolith condition 1, and gives an estimate of the average hour when fish were caught by the seabirds 33 FIGURE 17 Number of intact prey representing six prey groups present in the stomachs of flock-feeding species (top two graphs) and storm-petrels (bottom four) in relation to time-of-day that the birds were collected 34 FIGURE 18 Percent composition of the seven most frequently consumed prey species within the diets of seabirds feeding in flocks over yellowfin (Thunnus albacares) (light bar, N = 11 flocks) and skipjack tuna (Euthynnus pelamis) (dark bar, N = flocks) For a given flock type, percentages are the number of prey of a given prey species divided by the total number of prey representing all seven prey species multiplied by 100 Number of prey for the seven prey species was 471 individuals from birds collected over yellowfin tuna, and 206 prey from birds collected over skipjack tuna 36 FIGURE 19 Proportion of prey mass obtained by each of three species groups when using four feeding strategies Feeding over predatory fish is denoted by predatory fish; NCI = non-cephalopod invertebrates 42 APPENDICES APPENDIX PREY SPECIES BY NUMBER, MASS (GRAMS), AND PERCENT (BY NUMBER) IN THE DIETS OF 2,076 BIRDS OF 30 SPECIES SAMPLED IN THE ETP, 1983–1991 56 APPENDIX REGRESSION EQUATIONS USED TO CALCULATE STANDARD LENGTHS (SL), DORSAL MANTLE LENGTHS (DML), AND MASS (W) OF 19 SPECIES OF FISHES AND 17 SPECIES OF CEPHALOPODS EATEN BY ETP SEABIRDS 60 APPENDIX DIET OF BULWER’S PETREL (BULWERIA BULWERII) 64 APPENDIX DIET OF WHITE-FACED STORM-PETREL (PELAGODROMA MARINA) 65 APPENDIX DIET OF WHITE-THROATED STORM-PETREL (NESOFREGETTA FULIGINOSA) 66 APPENDIX DIET OF WHITE-BELLIED STORM-PETREL (FREGETTA GRALLARIA) 67 APPENDIX DIET OF LEACH’S STORM-PETREL (OCEANODROMA LEUCORHOA) 68 APPENDIX DIET OF WEDGE-RUMPED STORM-PETREL (OCEANODROMA TETHYS) 71 APPENDIX DIET OF MARKHAM’S STORM-PETREL (OCEANODROMA MARKHAMI) 73 APPENDIX 10 DIET OF STEJNEGER’S PETREL (PTERODROMA LONGIROSTRIS) 74 APPENDIX 11 DIET OF DEFILLIPPE’S PETREL (PTERODROMA DEFILIPPIANA) 76 APPENDIX 12 DIET OF WHITE-WINGED PETREL (PTERODROMA LEUCOPTERA) 77 APPENDIX 13 DIET OF BLACK-WINGED PETREL (PTERODROMA NIGRIPENNIS) 79 APPENDIX 14 DIET OF HERALD PETREL (PTERODROMA ARMINJONIANA) 81 APPENDIX 15 DIET OF MURPHY’S PETREL (PTERODROMA ULTIMA) 82 APPENDIX 16 DIET OF PHOENIX PETREL (PTERODROMA ALBA) 83 APPENDIX 17 DIET OF TAHITI PETREL (PTERODROMA ROSTRATA) 84 APPENDIX 18 DIET OF JUAN FERNANDEZ PETREL (PTERODROMA E EXTERNA) 87 APPENDIX 19 DIET OF WHITE-NECKED PETREL (PTERODROMA E CERVICALIS) 89 APPENDIX 20 DIET OF KERMEDEC PETREL (PTERODROMA NEGLECTA) 90 APPENDIX 21 DIET OF SOOTY SHEARWATER (PUFFINUS GRISEUS) 91 APPENDIX 22 DIET OF WEDGE-TAILED SHEARWATER (PUFFINUS PACIFICUS) 92 APPENDIX 23 DIET OF CHRISTMAS SHEARWATER (PUFFINUS NATIVITATUS) 93 APPENDIX 24 DIET OF SOOTY TERN (ONYCHOPRION FUSCATA) 94 APPENDIX 25 DIET OF WHITE TERN (GYGIS ALBA) 95 APPENDIX 26 DIET OF GRAY-BACKED TERN (ONYCHOPRION LUNATUS) 95 APPENDIX 27 DIET OF PARASITIC JAEGER (STERCORARIUS PARASITICUS) 96 APPENDIX 28 DIET OF RED-TAILED TROPICBIRD (PHAETHON RUBRICAUDA) 96 APPENDIX 29 DIET OF GREAT FRIGATEBIRD (FREGATA MINOR) 97 APPENDIX 30 DIET OF MASKED BOOBY (SULA DACTYLATRA) 97 APPENDIX 31 DIET OF NAZCA BOOBY (SULA GRANTI) 98 APPENDIX 32 DIET OF RED-FOOTED BOOBY (SULA SULA) 98 APPENDIX 33 MINIMUM DEPTH DISTRIBUTIONS OF MYCTOPHIDS DURING NOCTURNAL VERTICAL MIGRATIONS 99 LIST OF AUTHORS LARRY B SPEAR H.T Harvey & Associates 3150 Almaden Expressway, Suite 145 San Jose, CA 95118 Deceased DAVID G AINLEY H.T Harvey & Associates 3150 Almaden Expressway, Suite 145 San Jose, CA 95118 WILLIAM A WALKER National Marine Mammal Laboratory Alaska Fisheries Science Center National Marine Fisheries Service, NOAA 7600 Sand Point Way N.E Seattle, WA 98115 85 FORAGING DYNAMICS OF TROPICAL SEABIRDS—Spear et al APPENDIX 17 CONTINUED Melamphaes sp Scopeloberyx robusta Scopeloberyx sp Unidentified Melamphaidae Trachipteridae Trachipterus sp Percichthyidae Howella sp cf H brodei Coryphaenaidae Coryphaena sp Gempylidae Nesiarchus nasutus Rexea solandri Gempylus serpens Trichiuridae Trichiurus sp cf T nitens Unidentified teleosts Ommastrephidae Sthenoteuthis oualaniensis Ornithoteuthis volatilus Unidentified Ommastrephidae Onychoteuthidae Onychoteuthis banksii Pholidoteuthidae Pholidoteuthis bochmai Enoploteuthidae Pterygioteuthis giardi Abraliopsis sp Ancistrocheirus lesueuri Octopoteuthidae Octopoteuthis deletron Octopoteuthis sp Histioteuthidae Histioteuthis sp Histioteuthis hoylei Histioteuthis sp B Bathyteuthidae Bathyteuthis bacidifera Mastigoteuthidae Mastigoteuthis sp Chiroteuthidae Chiroteuthis calyx Chiroteuthis sp A Chiroteuthis spp Cranchiidae Cranchia scabra Liocranchia sp Liocranchia reinhardti Leachia dislocata Helicocranchia sp Liguriella sp Megalocranchia sp Taonius pavo Taonius sp A Unidentified Cranchiidae Octopoda Bolitaneidae Japetella heathi Alloposidae Alloposus mollis Number of prey 6 19 1 2 1 1 1 11 91 32 58 286 286 2 16 5 19 11 2 10 10 20 13 47 1 5 26 1 1 Prey occurrence % 0.6 0.4 0.6 2.0 0.1 – 0.2 – 0.1 – 0.4 0.2 0.1 0.1 0.1 – 0.0 9.7 3.4 0.1 6.2 30.6 – 0.2 – 1.7 0.7 0.2 0.5 0.5 0.2 0.3 2.0 0.7 1.2 0.1 0.2 – 1.1 – 2.1 0.4 0.3 1.4 5.0 0.1 0.1 0.2 0.5 0.1 0.5 0.2 2.8 0.1 0.3 0.2 0.1 – 0.1 – Mass (g) 29.2 22.5 30.5 116.1 4.2 4.2 8.0 8.0 25.0 25.0 48.0 24.0 12.0 12.0 4.8 4.8 0.0 441.0 254.8 9.8 176.4 1,744.6 1,744.6 36.0 36.0 36.0 6.0 4.8 25.2 60.0 24.0 36.0 312.0 36.0 264.0 12.0 24.0 24.0 36.0 36.0 240.0 48.0 36.0 156.0 297.5 12.0 5.5 22.0 60.0 12.0 36.0 36.0 108.0 6.0 0.0 9.6 4.8 4.8 4.8 4.8 Frequency 6 16 – – – 1 – 11 22 10 11 87 – – 14 15 – – 13 29 1 15 – – % 3.8 2.6 3.8 10.3 0.6 – 1.3 – 0.6 – 2.6 1.3 0.6 0.6 0.6 – 7.1 14.1 6.4 0.6 7.1 55.8 – 1.3 – 9.0 3.8 1.9 3.2 2.6 0.6 1.9 9.6 3.8 5.1 0.6 1.3 – 5.1 – 8.3 2.6 0.6 5.1 18.6 0.6 0.6 3.2 1.3 0.6 2.6 1.3 9.6 0.6 1.9 1.3 0.6 – 0.6 – 86 NO 35 STUDIES IN AVIAN BIOLOGY APPENDIX 17 CONTINUED Unidentified Cephalopoda Unidentified Teuthoidea Unidentified octopod Crustacea Unidentified crustacean Unidentified large shrimp Gerrid insect Halobates sp Snail Small snail Number of prey 16 94 1 20 20 13 13 Prey occurrence % 0.0 0.0 0.0 0.2 0.1 0.1 2.1 – 1.4 – Note: Sample size of petrels, N = 156, with prey 154; prey sample, N = 936 Mass (g) 0.0 0.0 0.0 0.27 0.12 0.15 0.6 0.6 1.8 1.8 Frequency 16 94 1 – – % 10.3 60.3 0.6 1.3 0.6 0.6 3.2 – 1.9 – 87 FORAGING DYNAMICS OF TROPICAL SEABIRDS—Spear et al APPENDIX 18 DIET OF JUAN FERNANDEZ PETREL (PTERODROMA EXTERNA) Fishes Cephalopods Misc invertebrates/eggs Engraulidae Unidentified Engraulidae Argentinidae Microstoma microstoma Nansenia sp Bathylagidae Bathylagus sp Sternoptychidae Sternoptyx diaphana Argyropelecus sladeni Argyropelecus sp Photichthyidae Viniguerria lucetia Ichthyococcus sp Chloropthalmidae Chloropthalmus sp Myctophidae Protomyctophum sp Hygophum sp cf H proximum Hygophum sp Diogenichthys laternatus Myctophum aurolaternatum Symbolophorus evermanni Lampadena luminosa Ceratoscopelus warmingii Lampanyctus nobilis Lampanyctus parvicauda Diaphus parri Diaphus lutkeni Diaphus sp Gonichthys tenuiculus Unidentified Myctophidae Scomberosocidae Scomberesox scombroides Hemirhamphidae Oxyporhamphus micropterus Unidentified Hemirhamphidae Exocoetidae Exocoetus spp Cypselurus exilens Cypselurus spilonotopterus Cypselurus sp Unidentified Exocoetidae Moridae Unidentified Moridae Bregmacerotidae Bregmaceros bathymaster Bregmaceros sp Macrouridae Unidentified Macrouridae Diretmidae Diretmus argenteus Diretmus sp Melamphaidae Melamphaes longivelis Melamphaes sp Scopeloberyx robusta Scopeloberyx sp Unidentified Melamphaidae Number of prey 599 485 10 187 187 1 16 1 1 68 2 24 2 107 104 155 92 1 60 1 2 25 24 16 4 Prey occurrence % 54.7 44.3 0.9 17.1 – 0.3 0.2 0.1 0.1 – 1.5 0.5 0.3 0.7 0.2 0.1 0.1 0.1 – 6.2 0.1 0.3 0.3 0.1 0.6 0.4 0.1 0.7 0.5 0.2 0.2 0.2 0.4 0.1 2.2 0.2 0.2 9.8 9.5 0.3 14.2 8.4 0.1 0.1 0.1 5.5 0.1 – 0.8 0.7 0.1 0.2 – 2.3 2.2 0.1 1.5 0.3 0.4 0.3 0.4 0.2 Mass (g) 6,338.6 5,335.0 1.5 261.8 261.8 15.3 8.8 6.5 4.8 4.8 94.7 35.6 14.6 44.5 2.8 1.4 1.4 4.8 4.8 324.8 4.6 15.5 10.5 4.6 33.2 22.1 4.2 39.1 27.7 9.0 9.4 8.7 17.4 4.6 114.2 9.8 9.8 2,140.0 2,080.0 60.0 3,100.0 1,840.0 20.0 20.0 20.0 1,200.0 6.6 6.6 45.7 40.9 4.8 9.6 9.6 193.3 188.4 4.9 89.2 13.4 31.0 15.2 20.8 8.8 Frequency 167 148 10 – 1 – 13 3 1 – 54 7 2 2 18 – 59 56 90 55 1 46 – – 15 14 14 3 % 78.0 69.2 4.7 0.5 – 0.9 0.5 0.5 0.5 – 6.1 1.4 1.4 3.3 0.9 0.5 0.5 0.5 – 25.2 0.5 1.4 0.9 0.5 3.3 1.9 0.5 3.3 2.8 0.9 0.9 0.9 0.9 0.5 8.4 0.5 – 27.6 26.2 1.4 42.1 25.7 0.5 0.5 0.5 21.5 0.5 – 3.7 3.3 0.5 0.9 – 7.0 6.5 0.5 6.5 1.4 1.4 1.4 1.9 0.9 88 NO 35 STUDIES IN AVIAN BIOLOGY APPENDIX 18 CONTINUED Percichthyidae Howella sp cf H brodei Gempylidae Nesiarchus nasutus Gempylus serpens Unidentified teleosts Ommastrephidae Sthenoteuthis oualaniensis Dosidicus gigas Hyaloteuthis pelagica Ornithoteuthis volatilus Unidentified Ommastrephidae Onychoteuthidae Onychoteuthis banksii Pholidoteuthidae Pholidoteuthis boschmai Enoploteuthidae Pterygioteuthis giardi Abraliopsis affinis Abraliopsis sp Ancistrocheirus lesueuri Octopoteuthidae Octopoteuthis sp Histioteuthidae Histioteuthis sp Histioteuthis sp cf H hoylei Histioteuthis sp B Histioteuthis corona Bathyteuthidae Bathyteuthis bacidifera Mastigoteuthidae Mastigoteuthis sp Mastigoteuthis sp A Chiroteuthidae Chiroteuthis sp A Chiroteuthis sp Cranchiidae Liocranchia sp Liocranchia reinhardti Leachia dislocata Liguriella sp Megalocranchia sp Taonius pavo Galiteuthis pacifica Unidentified Cranchiidae Octopoda Tremoctopodidae Tremoctopus violaceus Ocythoidae Ocythoe tuberculata Unidentified Cephalopoda Unidentified Teuthoidea Crustacea Unidentified crustacean Gammarid/hyperiid amphipod Cymothoid, Nerocila sp Unidentified large shrimp Gerrid insect Halobates sp Number of prey % 0.2 – 0.2 0.1 0.1 15 1.4 279 25.5 181 16.5 0.3 0.2 0.1 92 8.4 122 11.1 122 – 0.3 – 15 1.4 0.1 0.2 0.6 0.4 0.3 – 16 1.5 0.3 0.5 0.5 0.2 0.1 – 0.3 0.2 0.1 0.6 0.5 0.2 33 3.0 0.3 0.1 0.1 0.3 0.4 17 1.6 0.2 0.2 0.3 0.1 – 0.2 – 17 0.0 172 0.0 0.8 0.2