Shadowed by scale: subtle behavioral niche partitioning in two sympatric, tropical breeding albatross species

Abstract

BackgroundTo meet the minimum energetic requirements needed to support parents and their provisioned offspring, the timing of breeding in birds typically coincides with periods of high food abundance. Seasonality and synchrony of the reproductive cycle is especially important for marine species that breed in high latitudes with seasonal booms in ocean productivity. Laysan and black-footed albatrosses breeding in the northwestern Hawaiian Islands have a dual reliance on both seasonally productive waters of high latitudes and on nutrient-poor waters of low latitudes, because their foraging ranges contract during the short but critical brood-guard stage. Therefore, these species face an additional constraint of having to negotiate nutrient-poor waters during the most energetically-demanding stage of the breeding cycle. This constriction of foraging range likely results in a higher density of foraging competitors. Thus, our aim was to understand how Hawaiian albatross partition resources both between and within species in this highly constrained breeding stage while foraging in less productive waters and simultaneously experiencing increased competition. High-precision GPS dataloggers were deployed on black-footed (Phoebastria nigripes, n=20) and Laysan (Phoebastria immutabilis, n=18) albatrosses during the brood-guard stage of the breeding season in 2006 (n=8), 2009 (n=13), 2010 (n=16) and 2012 (n=1). We used GPS data and movement analyses to identify six different behavioral states in foraging albatrosses that we then used to characterize foraging trips across individuals and species. We examined whether variations in behavior were correlated with both intrinsic factors (sex, body size, body condition) and extrinsic factors (lunar phase, wind speed, year).ResultsBehavioral partitioning was revealed both between and within species in Hawaiian albatrosses. Both species were highly active during chick-brooding trips and foraged across day and night; however, Laysan albatrosses relied on foraging at night to a greater extent than black-footed albatrosses and exhibited different foraging patterns at night. For both species, foraging along direct flight paths and foraging on the water in a “sit-and-wait” strategy were just as prevalent as foraging in a searching flight mode, indicating flexibility in foraging strategies in Hawaiian albatross. Both species strongly increased drift forage at night when the lunar phase was the darkest, suggesting Hawaiian albatross feed on diel vertically-migrating prey to some extent. Black-footed albatrosses showed greater variation in foraging behavior between individuals which suggests a higher level of intra-specific competition. This behavioral variability in black-footed albatrosses was not correlated with sex or body size, but differences in body condition suggested varying efficiencies among foraging patterns. Behavioral variability in Laysan albatrosses was correlated with sex, such that females exhibited greater flight foraging than drift foraging, had longer trip durations and f...

Ontogenetic changes in at-sea distributions of immature short-tailed albatrosses Phoebastria albatrus

“…This seasonal shift in distributions could also indicate a reliance on or preference for daytime foraging strategies by immature individuals. Like Hawaiian albatrosses (Conners et al 2015), adult short-tailed albatrosses may forage at night (Suryan et al 2007); however, the extent to which this is region specific or important for immature birds is currently unknown.…”

Persistent annual migration patterns of a specialist seabird

“…A land mask (0.25° × 0.25°, NOAA OI SST V2 High Resolution Dataset) prevented the selection of points on land; however, this did not prohibit tracks from crossing land, particularly the Kamchatka (n = 14) and Alaska Peninsulas (n = 3), which are narrow enough for a kittiwake to cross in one 12 h period. Estimated travel speed of each individual was included for dry ; Conners et al 2015) activity bins. Double tagging with GPS data loggers indicates that a median error in locations associated with this method (calculated at similar latitudes) is 185 km for the solstice and 145 km for equinox periods (Merkel et al 2016).…”

Fisheries Exploitation by Albatross Quantified With Lipid Analysis

“…North Pacific albatrosses are opportunistic foragers and consume a wide variety of prey using flexible foraging tactics (Harrison et al, 1983;Gould et al, 1997;Tickell, 2000;Conners et al, 2015); therefore, collecting a library of all potential prey species for lipid analysis would be both impractical and quantitatively unfeasible given limitations of the QFASA model itself. However, since the fatty acid composition of an organism is influenced by its feeding ecology (Budge et al, 2006), collecting species from across the range of functional groups regularly consumed by a predator theoretically should represent the range of lipids consumed by the predator.…”

“…and euphausiid krill (Euphausiia pacifica) to a larger mysid (Boreomysis kinkaidi) and the very large deep-sea shrimp (Acanthephyra purpurea). Crustaceans may be accessible to albatrosses through a drift foraging strategy or opportunistically (Miller, 1940;Conners et al, 2015). Five species of myctophid fish (Diaphus theta, Lampanyctus jordani, Lampadena urophaos, Stenobrachius leucopsaurus, and Tarletonbeania taylori) were grouped as a mesopelagic fish functional group (MYC).…”