Foraging specificity and prey utilization: evaluating social and memory-based strategies in seabirds

in Behaviour
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This study explores the capacity for seabirds to exhibit behavioral plasticity in response to the predictability of resources. Using direct species-comparisons, I tested the hypothesis that roseate terns (Sterna dougallii), dietary specialists, rely more heavily on foraging site-fidelity to pursue persistent prey, whereas common terns (S. hirundo), prey generalists, depend more on local enhancement by exploiting mixed-species assemblages. I analysed chick-provisioning observations and the bearings of commuting trajectories between the shared breeding colony, foraging areas, and feeding flocks. Foraging route patterns in roseate terns were consistent with a strategy based more heavily on spatial memory than social cues, in contrast to common terns, which associated more readily with nearby feeding aggregations, in line with social facilitation. Only during years of high prey abundance did roseate terns outperform common terns in nest productivity and the quality of prey delivered to chicks, suggesting that opportunistic tactics support resilience to sparse prey availability.

Foraging specificity and prey utilization: evaluating social and memory-based strategies in seabirds

in Behaviour

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References

AgostinelliC.LundU. (2011). R package ‘circular’: circular statistics. — Version 0.4-3 available online at http://CRAN.R-project.org/package=circular.

AuD.W.K.PitmanR.L. (1986). Seabird interactions with dolphins and tuna in the eastern tropical Pacific. — Condor 88: 304-317.

BaldaR.KamilA. (2006). The ecology and life history of seed caching corvids. — In: Animal spatial cognition: comparative neural and computational approaches ( BrownM.F.CookR.G. eds) available online at http://www.pigeon.psy.tufts.edu/asc/.

BaldaR.P.KamilA.C.BednekoffP.A. (1996). Predicting cognitive capacity from natural history: examples from four species of corvids. — Curr. Ornithol. 13: 33-66.

BarrettR.T.CamphuysenK.Anker-NilssenT.ChardineJ.W.FurnessR.W.GartheS.HuppopO.LeopoldM.F.MontevecchiW.A.VeitR.R. (2007). Diet studies of seabirds: a review and recommendations. — ICES J. Mar. Sci. 64: 1675-1691.

BeckerP.H.FrankD.SudmannS.R. (1993). Temporal and spatial pattern of common tern (Sterna hirundo) foraging in the Wadden Sea. — Oecologia 93: 389-393.

BeckerP.H.EzardT.H.G.LudwigsJ.D.Sauer-GürthH.WinkM. (2008). Population sex ratio shift from fledging to recruitment: consequences for demography in a philopatric seabird. — Oikos 117: 60-68.

BednekoffP.A.BaldaR.P. (1996a). Observational spatial memory in Clark’s nutcrackers and Mexican jays. — Anim. Behav. 52: 833-839.

BednekoffP.A.BaldaR.P. (1996b). Social caching and observational spatial memory in pinyon jays. — Behaviour 133: 807-826.

BonadonnaF.BenhamouS.JouventinP. (2003). Orientation in “featureless” environments: the extreme case of pelagic birds. — In: Avian migration ( BertholdP.GwinnerE.SonnenscheinE. eds). SpringerBerlin p.  367-377.

BrunoJ.F.StachowiczJ.J.BertnessM.D. (2003). Inclusion of facilitation into ecological theory. — Trends Ecol. Evol. 18: 119-125.

BuckleyN.J. (1997). Spatial-concentration effects and the importance of local enhancement in the evolution of colonial breeding in seabirds. — Am. Nat. 149: 1091-1112.

BurkeC.M.MontevecchiW.A. (2009). The foraging decisions of a central place foraging seabird in response to fluctuations in local prey conditions. — J. Zool. 278: 354-361.

BurnessG.P.MorrisR.D.BruceJ.P. (1994). Seasonal and annual variation in brood attendance, prey type delivered to chicks, and foraging patterns of male common terns (Sterna hirundo). — Can. J. Zool. 72: 1243-1251.

BUZM3 (2011). National Oceanic and Atmospheric Administration (NOAA) national data buoy center (NDBC). — Available online at http://www.ndbc.noaa.gov/station_history.php?station=buzm3.

DänhardtA.BeckerP.H. (2011). Does small-scale vertical distribution of juvenile schooling fish affect prey availability to surface-feeding seabirds in the Wadden Sea?J. Sea Res. 65: 247-255.

DavorenG.K.MontevecchiW.A.AndersonJ.T. (2003). Search strategies of a pursuit-diving marine bird and the persistence of prey patches. — Ecol. Monogr. 73: 463-481.

DiamondA.W.DevlinC.M. (2003). Seabirds as indicators of changes in marine ecosystems: ecological monitoring on Machias Seal Island. — Environ. Monit. Assess. 88: 153-175.

DuffyD.C. (1986). Foraging at patches: interactions between common and roseate terns. — Ornis. Scand. 17: 47-52.

DunnE.K. (1972). Studies on terns with particular reference to feeding ecology. — PhD dissertation University of Durham Durham NC.

ElliottK.H.BullR.D.GastonA.J.DavorenG.K. (2009a). Underwater and above-water search patterns of an Arctic seabird: reduced searching at small spatiotemporal scales. — Behav. Ecol. Sociobiol. 63: 1773-1785.

ElliottK.H.WooK.J.GastonA.J.BenvenutiS.Dall’antoniaL.DavorenG.K. (2009b). Central-place foraging in an Arctic seabird provides evidence for Storer-Ashmole’s halo. — Auk 126: 613-625.

ErwinR.M. (1977). Foraging and breeding adaptations to different food regimes in three seabirds: the common tern, Sterna hirundo, royal tern, Sterna maxima, and black skimmer, Rynchops niger. — Ecology 58: 389-397.

Esri (2012). Arcgis desktop 10.0. — Environmental Systems Research Institute Redlands CA.

FaganW.F.LewisM.A.Auger-MéthéM.AvgarT.BenhamouS.BreedG.LadageL.SchlägelU.E.TangW.-W.PapastamatiouY.P.ForesterJ.MuellerT. (2013). Spatial memory and animal movement. — Ecol. Lett. 16: 1316-1329.

FauchaldP. (2009). Spatial interaction between seabirds and prey: review and synthesis. — Mar. Ecol. Prog. Ser. 391: 139-151.

GochfeldM.BurgerJ. (1982). Feeding enhancement by social attraction in the sandwich tern. — Behav. Ecol. Sociobiol. 10: 15-17.

GochfeldM.BurgerJ.NisbetI.C.T. (1998). Roseate tern (Sterna dougallii). — In: The birds of North America ( PooleA. ed.). Cornell Lab of OrnithologyIthaca, NY available online at http://bna.birds.cornell.edu/bna/species/370.

GoodenoughJ.McGuireB.WallaceR.A. (2001). Perspectives on animal behavior. — WileyNew York, NY.

GotmarkF. (1990). A test of the information-center hypothesis in a colony of sandwich terns Sterna sandvicensis. — Anim. Behav. 39: 487-495.

GoyertH.F. (2014). Relationship among prey availability, habitat, and the foraging behavior, distribution, and abundance of common terns Sterna hirundo and roseate terns S. dougallii. — Mar. Ecol. Prog. Ser. 506: 291-302.

GoyertH.F.ManneL.L.VeitR.R. (2014). Facilitative interactions among the pelagic community of temperate migratory terns, tunas and dolphins. — Oikos 123: 1400-1408.

GrémilletD.BoulinierT. (2009). Spatial ecology and conservation of seabirds facing global climate change: a review. — Mar. Ecol. Prog. Ser. 391: 121-137.

GrossM.R. (1996). Alternative reproductive strategies and tactics: diversity within sexes. — Trends Ecol. Evol. 11: 92-98.

GrünbaumD.VeitR.R. (2003). Black-browed albatrosses foraging on Antarctic krill: density-dependence through local enhancement?Ecology 84: 3265-3275.

HackerS.D.GainesS.D. (1997). Some implications of direct positive interactions for community species diversity. — Ecology 78: 1990-2003.

HeinemannD. (1992). Foraging ecology of roseate terns breeding on Bird Island Buzzards Bay Massachusetts. — USFWS Manomet MA.

HislopJ.R.G.HarrisM.P.SmithJ.G.M. (1991). Variation in the calorific value and total energy content of the lesser sandeel (Ammodytes marinus) and other fish preyed on by seabirds. — J. Zool. 224: 501-517.

IronsD.B. (1998). Foraging area fidelity of individual seabirds in relation to tidal cycles and flock feeding. — Ecology 79: 647-655.

KingJ.R.CamisaM.J.ManfrediV.M. (2010). Massachusetts Division of Marine Fisheries trawl survey effort list of species and bottom temperature trends 1978–2007. — MADMFNew Bedford, MA.

KirkhamI.R. (1986). Comparative foraging and breeding habits of Arctic and common terns. — PhD dissertation Dalhousie University Halifax NS.

KMAMARIO3 (2011). Weather underground. — Available online at http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KMAMARIO3.

LackD.L. (1946). Competition for food by birds of prey. — J. Anim. Ecol. 15: 123-129.

LackD.L. (1968). Ecological adaptations for breeding in birds. — MethuenLondon.

LanghamN.P.E. (1968). The comparative biology of terns Sterna spp. — PhD dissertation University of Durham Durham NC.

MassGIS (2013). Office of Geographic Information Commonwealth of Massachusetts Information Technology Division. — Avaiable online at http://www.mass.gov.

MontevecchiW.A.BenvenutiS.GartheS.DavorenG.K.FifieldD. (2009). Flexible foraging tactics by a large opportunistic seabird preying on forage- and large pelagic fishes. — Mar. Ecol. Prog. Ser. 385: 295-306.

MostelloC.S. (2010). Inventory of terns laughing gulls and black skimmers nesting in Massachusetts in 2009. — MDFW Natural Heritage and Endangered Species Program (NHESP) Westborough MA.

MostelloC.S. (2011). Inventory of terns laughing gulls and black skimmers nesting in Massachusetts in 2010. — MDFW NHESP Westborough MA.

MostelloC.S. (2012). Inventory of terns laughing gulls and black skimmers nesting in Massachusetts in 2011. — MDFW NHESP Westborough MA.

NisbetI.C.T. (2002). Common tern (Sterna hirundo). — In: The birds of North America ( PooleA. ed.). Cornell Lab of OrnithologyIthaca, NY available online at http://bna.birds.cornell.edu/bna/species/618.

NisbetI.C.T.DruryW.H. (1972). Measuring breeding success in common and roseate terns. — Bird-Banding 43: 97-106.

NisbetI.C.T.MostelloC.S.VeitR.R.FoxJ.W.AfanasyevV. (2011). Migration and winter quarters of five common terns tracked using geolocators. — Waterbirds 34: 32-39.

NisbetI.C.T.SpendelowJ.A. (1999). Contribution of research to management and recovery of the roseate tern: review of a twelve-year project. — Waterbirds 22: 239-252.

OriansG.H.PearsonN.E. (1979). On the theory of central place foraging. — In: Analysis of ecological systems ( HornD.J.MitchellR.D.StairsG.R. eds). Ohio State University PressColumbus, OH p.  155-177.

OverholtzW.J.JacobsonL.D.MelvinG.D.CieriM.PowerM.LibbyD.ClarkK. (2004). Gulf of Maine — Georges Bank Atlantic herring complex 2003. — Northeast Fisheries Science Center Woods Hole MA.

OverholtzW.J.LinkJ.S.SuslowiczL.E. (2000). Consumption of important pelagic fish and squid by predatory fish in the northeastern USA shelf ecosystem with some fishery comparisons. — ICES J. Mar. Sci. 57: 1147-1159.

PallaudB. (1984). Hypotheses on mechanisms underlying observational learning in animals. — Behav. Process. 9: 381-394.

PerrowM.R.SkeateE.R.GilroyJ.J. (2011). Visual tracking from a rigid-hulled inflatable boat to determine foraging movements of breeding terns. — J. Field Ornithol. 82: 68-79.

PinheiroJ.BatesD.DebroyS.SarkarD. & R Development Core Team (2013). nlme: linear and nonlinear mixed effects models. — R package version 3.1-113 available online at http://CRAN.R-project.org/package=nlme.

PoysaH. (1992). Group foraging in patchy environments: the importance of coarse-level local enhancement. — Ornis. Scand. 23: 159-166.

R Development Core Team. (2012). R: a language and environment for statistical computing. Version 2.15.0. — R Foundation for Statistical ComputingVienna available online at http://www.R-project.org.

RacineF.GiraldeauL.A.Patenaude-MonetteM.GirouxJ.F. (2012). Evidence of social information on food location in a ring-billed gull colony, but the birds do not use it. — Anim. Behav. 84: 175-182.

RamosJ.A. (2000). Characteristics of foraging habitats and chick food provisioning by tropical roseate terns. — Condor 102: 795-803.

RegularP.M.HeddA.MontevecchiW.A. (2013). Must marine predators always follow scaling laws? Memory guides the foraging decisions of a pursuit-diving seabird. — Anim. Behav. 86: 545-552.

RobardsM.D.AnthonyJ.A.RoseG.A.PiattJ.F. (1999). Changes in proximate composition and somatic energy content for Pacific sand lance (Ammodytes hexapterus) from Kachemak Bay, Alaska relative to maturity and season. — J. Exp. Mar. Biol. Ecol. 242: 245-258.

RobertsD. (1941). Imitation and suggestion in animals. — Bull. Anim. Behav. 1: 11-19.

RockJ.C.LeonardM.L.BoyneA.W. (2007). Foraging habitat and chick diets of roseate tern, Sterna dougallii, breeding on Country Island, Nova Scotia. — Avian Conserv. Ecol. 2: 4.

SafinaC. (1990a). Bluefish mediation of foraging competition between roseate and common terns. — Ecology 71: 1804-1809.

SafinaC. (1990b). Foraging habitat partitioning in roseate and common terns. — Auk 107: 351-358.

SafinaC.BurgerJ. (1988). Ecological dynamics among prey fish, bluefish, and foraging common terns in an Atlantic coastal system. — In: Seabirds and other marine vertebrates: competition predation and other interactions ( BurgerJ. ed.). Columbia University PressNew York, NY p.  95-173.

SafinaC.BurgerJ.GochfeldM.WagnerR.H. (1988). Evidence for prey limitation of common and roseate tern reproduction. — Condor 90: 852-859.

SafinaC.WagnerR.H.WittingD.A.SmithK.J. (1990). Prey delivered to roseate and common tern chicks; composition and temporal variability. — J. Field Ornithol. 61: 331-338.

ScheidC.BugnyarT. (2008). Short-term observational spatial memory in jackdaws (corvus monedula) and ravens (corvus corax). — Anim. Cogn. 11: 691-698.

SeedA.EmeryN.ClaytonN. (2009). Intelligence in corvids and apes: a case of convergent evolution?Ethology 115: 401-420.

ShealerD.A. (1998). Size-selective predation by a specialist forager, the roseate tern. — Auk 115: 519-525.

SilvermanE.D.VeitR.R.NevittG.A. (2004). Nearest neighbors as foraging cues: information transfer in a patchy environment. — Mar. Ecol. Prog. Ser. 277: 25-35.

SpendelowJ.A.HinesJ.E.NicholsJ.D.NisbetI.C.T.CormonsG.HaysH.HatchJ.J.MostelloC.S. (2008). Temporal variation in adult survival rates of roseate terns during periods of increasing and declining populations. — Waterbirds 31: 309-319.

SzostekK.BeckerP. (2012). Terns in trouble: demographic consequences of low breeding success and recruitment on a common tern population in the German Wadden Sea. — J. Ornithol. 153: 313-326.

ThorpeW.H. (1951). The learning abilities of birds. — Ibis 93: 252-296.

TimsJ.NisbetI.C.T.FriarM.S.MostelloC.HatchJ.J. (2004). Characteristics and performance of common terns in old and newly-established colonies. — Waterbirds 27: 321-332.

WaltzE.C. (1987). A test of the information center hypothesis in 2 colonies of common terns, Sterna hirundo. — Anim. Behav. 35: 48-59.

WardP.ZahaviA. (1973). The importance of certain assemblages of birds as “information-centres” for food-finding. — Ibis 115: 517-534.

WeimerskirchH. (2007). Are seabirds foraging for unpredictable resources?Top. Stud. Oceanogr. 54: 211-223.

WeimerskirchH.BertrandS.SilvaJ.MarquesJ.C.GoyaE. (2010). Use of social information in seabirds: compass rafts indicate the heading of food patches. — PLoS ONE 5: e9928.

WickhamH. (2009). ggplot2: elegant graphics for data analysis. — SpringerNew York, NY available online at http://ggplot2.org/.

WikelskiM.KaysR.W.KasdinN.J.ThorupK.SmithJ.A.SwensonG.W. (2007). Going wild: what a global small-animal tracking system could do for experimental biologists. — J. Exp. Biol. 210: 181-186.

WittenbergerJ.F.HuntG.L.Jr. (1985). The adaptive significance of coloniality in birds. — In: Avian biology ( FarnerD.KingJ.ParkesK. eds). Academic PressNew York, NY p.  1-78.

WoodS.N. (2006). Generalized additive models: an introduction with R. — Chapman & Hall/CRCNew York, NY.

YoergS.I. (2001). Clever as a fox: animal intelligence and what it can teach us about ourselves. — BloomsburyNew York, NY.

ZarJ.H. (2010). Biostatistical analysis. — Prentice HallUpper Saddle River, NJ.

Figures

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    Wind directions at the study site. (a) One of the largest shared breeding grounds of both common and roseate terns in North America: Buzzards Bay, MA, USA, which includes Bird, Ram and Penikese Islands. (b) Buzzards Bay magnified: rose diagram (circular frequency histogram) of mean wind direction for all colony-level scans, at Bird Island. The black arrow represents the mean, and the black arc represents the 95% confidence interval. Data were downloaded online for the mouth of Buzzards Bay via NOAA weather station BUZM3 (2009), and for Marion inner harbour via KMAMARIO3 (2011). These maps were produced using ArcGIS Desktop 10.0 (ESRI 2012), with land feature and bathymetry data layers from the online Office of Geographic Information (MassGIS). This figure is published in colour in the online edition of this journal, which can be accessed via http://booksandjournals.brillonline.com/content/journals/1568539x.

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    Study design to test three foraging strategy hypotheses from correlations among flight directions and bearings of mixed-species feeding flocks. Positively-correlated angles of individual and colony-level departures and returns, and bearings of mixed-species feeding aggregations, are consistent with three foraging strategy hypotheses (Davoren et al., 2003; Weimerskirch et al., 2010), across three seasons at Bird Island. Axes denote cardinal directions on a compass (large black circles), with colony location at the centre. Black arrows: returns; dashed arrows: departures; single arrows: mean directions of marked individuals; multiple arrows: mean directions of the sampled colony; bird in flight: mixed-species feeding assemblages. Rows define the tested hypotheses, and columns represent sampling periods: either 1-h stints observing marked individuals, or 40-min scans of the colony. Correlation tests were conducted on commuting trajectories within sampling periods (left column) and across consecutive sampling periods (‘∼’ indicates between scans, within days). The relationships of significant correlations (positive or negative, p<0.05) indicate species-specific predictions and results, comparing roseate (RT, Sterna dougallii) to common terns (CT, S. hirundo). Significant positive correlations between: (a) individual departures and colony-level departures or returns show reliance on individual-level foraging fidelity (a combination of social and memory-based tactics); successive, positively correlated departures of marked individuals are in line with heavier dependence on spatial memory than information exchange, as predicted in roseate terns. Positive correlations among (b) colony-level departures and returns within scans, or between scans within a day, provide evidence for colony-level fidelity, as expected for both roseate and common terns. Positively correlated (c) bearings of feeding flocks and mean directions of colony-level departures or returns, within a scan, illustrate social facilitation (local enhancement) as predicted in common terns; negative correlations point towards competitive interactions (as with roseate terns). See Figure A4 for more detail. This figure is published in colour in the online edition of this journal, which can be accessed via http://booksandjournals.brillonline.com/content/journals/1568539x.

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    Size of the three dominant fish delivered to chicks, by tern species, year, and prey category. Roseate terns (RT) delivered longer sandlance (‘Sl’), especially in 2009–2010. For the three years combined, (a) roseate terns delivered sandlance (μ=1.7) that were significantly longer than those delivered by common terns (CT, μ=1.6, p<0.05), and significantly longer than herring (‘Hg’) or anchovy (‘An’) delivered by either tern species (p<0.001). More specifically, there was a significant interaction of year with (b) tern species (F2,995=31.9, p<0.001) and with (c) prey category (F4,995=11.2, p<0.001). In the first two years, roseate terns delivered significantly longer sandlance than did common terns (p<0.05); compared to 2009, significantly shorter sandlance were delivered in 2011 by both roseate and common terns (p<0.001). Points and bars indicate mean ± standard error. This figure is published in colour in the online edition of this journal, which can be accessed via http://booksandjournals.brillonline.com/content/journals/1568539x.

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    Sampled spring abundance of the three dominant prey categories by year. Sandlance (‘Sl’) was significantly more abundant in 2009 than in 2010–2011 (p<0.05). There was a significant effect on abundance (average number at length per 15 × 15 km cell) by prey category (F2,231=4.1, p<0.05) and year (F2,231=4.5, p<0.05). Anchovy (‘An’) abundance was negligible, as they are more common in the fall. Points and bars indicate mean ± standard error, herring = ‘Hg’. This figure is published in colour in the online edition of this journal, which can be accessed via http://booksandjournals.brillonline.com/content/journals/1568539x.

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    Directions and relative frequencies of population-level routes to and from Bird Island during the 2009–2011 breeding seasons, observed from the lighthouse. The black arrow represents the mean direction, with a narrow 95% confidence interval arc, calculated by simple bootstrap using the concentration parameter kappa for a von Mises distribution, for: (a) common tern (CT) departures (N=12284), (b) common tern returns (N=10148), (c) roseate tern (RT) departures (3606), and (d) roseate tern returns (3467).

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    Relative frequencies of individual-level departures from Bird Island during the 2010–2011 breeding seasons, observed from blinds. The black arrow represents the mean direction, with a 95% confidence interval arc, for: (a) common terns (CT, N=204 departures of 61 individuals) and (b) roseate terns (RT, N=92 departures of 43 individuals).

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    Predicting foraging strategy and tactics from prey utilization, in the context of prey specificity and availability. If roseate terns pursue specific prey items that highly dominate their diet and are highly predictable in their availability, then it would be adaptive to use a highly memory-based strategy to revisit feeding hotspots, with spatial memory as the tactic of choice. Because roseate terns (grey shading) have a diet that is low in diversity, and low in transience (high in persistence), then they are less likely to use a social or facilitative strategy. Common terns rely on prey that are low in dominance and low in predictability, therefore, they are less likely to use spatial memory. Instead, they select a highly diverse set of patchy, highly transient prey, and thereby benefit from the use of a highly social strategy for opportunistic foraging on facilitative cues (e.g., local enhancement). In other words, if terns cannot remember where the food is, then they may turn to others for clues.

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    Sampled spring distribution of the three dominant prey categories by year. Counts of (a) sandlance, herring, and (b) anchovy (up to 15 cm long), averaged into 30 square grid cells, each 15 × 15 km (225 km2). Interspersed black dots represent prey sampling stations, white cells indicate missing data (areas of no survey coverage). The black boxes (a) outline cells of persistent prey distribution across the three inshore bottom trawl surveys (mid-May, 2009–2011), conducted by the Massachusetts Division of Marine Fisheries (MADMF; King et al., 2010). This figure is published in colour in the online edition of this journal, which can be accessed via http://booksandjournals.brillonline.com/content/journals/1568539x.

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    Depiction of Table 2 to visualize correlations in flight patterns, for tests of foraging strategy hypotheses. Relationships (positive or negative) of significant circular correlation coefficients (∗∗∗p<0.001, ∗∗p<0.01, p<0.05) among theoretical angles of departure or return (single arrows, marked individuals; double arrows, colony), and feeding flocks (tern in flight) indicate which test results are consistent with common (CT, blue) and roseate tern (RT, red) foraging fidelity, social interactions (facilitation or competition), or memory use. Observations recorded within 40-min colony-level scans are separated by minutes; within-day correlations between observations, up to hours apart, suggest the persistence of patterns, either between scans or between 1-h individual stints. Axes denote cardinal directions on a compass, with Bird Island at the centre. See Figure 2 for more details. This figure is published in colour in the online edition of this journal, which can be accessed via http://booksandjournals.brillonline.com/content/journals/1568539x.

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    Per capita chick provisioning rates by tern species. Across all years combined, provisioning rates of common terns (number of prey delivered per hour) were significantly higher than those of roseate terns, both by nest (t147.2=3.8, p<0.001), and by chick (t147.8=2.8, p<0.01, above, mean ± standard error bars).

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    Size of prey deliveries related to travel directions. Terns delivered significantly longer prey to their chicks after departures to the southeast, according to a generalized additive mixed model (GAMM), using individual as a random effect: F2,53=12.7, R2=0.26, p<0.001.

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    Images of a common and roseate tern carrying sandlance. A common tern with sandlance (a) and roseate tern with two sandlance (b), a rarely photo-documented event since terns are generally single-prey loaders. This figure is published in colour in the online edition of this journal, which can be accessed via http://booksandjournals.brillonline.com/content/journals/1568539x.

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