Abstract:To successfully exploit resources, animals must be adapted to operate under phenotypic and environmental constraints. The strategies that predators use to locate prey are therefore diverse, particularly for breeding central-place foragers that must balance investment in reproduction and self-maintenance. Magnificent frigatebirds Fregata magnificens are tropical seabirds with intriguing morphology and feeding ecology, which display strikingly unequal levels of parental care (males deserting offspring months bef… Show more
“…Blue whales have been shown to adjust their dive behavior based on the density of prey in the area (Goldbogen et al, 2015;Hazen et al, 2015), so it is possible they encountered prey in insufficient concentrations for them to feed upon. More broadly, males and females of central-place foragers are known to have different sex-based foraging strategies arising from different energetic requirements during reproduction and resulting in differential exploitation of the offshore and coastal environment (Breed et al, 2006;Austin et al, 2019). A similar process could be driving the observed differences between male blue and fin whales.…”
Intermediate-duration archival tags were attached to eight blue whales (Balaenoptera musculus; four females, three males, one of unknown sex), and five fin whales (B. physalus; two females, one male, two of unknown sex) off southern California, USA, in summer 2014 and 2015. Tags logged 1-Hz data from tri-axial accelerometers, magnetometers, and a depth sensor, while acquiring Fastloc GPS locations. Tag attachment duration ranged from 18.3 to 28.9 d for blue whales and 4.9-16.0 d for fin whales, recording 1,030-4,603 dives and 95-3,338 GPS locations per whale across both species. Feeding lunges (identified from accelerometer data) were used to characterize "feeding bouts" (i.e., sequences of feeding dives with <60 min of consecutive non-feeding dives), within-bout behavior, and to examine the spatial distribution of feeding effort. Whales fed near the tagging locations (Point Mugu and San Miguel Island) for up to 7 d before dispersing as far south as Ensenada, Mexico, and north to Cape Mendocino, California. Dispersal within southern California waters differed by sex in both species with males undertaking offshore, circuitous excursions, while females remained more coastal, suggesting that movement patterns on the feeding grounds may not be exclusively related to energy gain. Feeding bout characteristics were similar for both species, with the median bout having 24 dives and lasting 3.3 h for blue whales (n = 242), and 19 dives while lasting 2.7 h for fin whales (n = 59). Bout duration was positively correlated with the number of feeding lunges per dive within a bout for both species, suggesting whales left poor-quality prey patches quickly but fed intensively for up to 34.9 h when prey was abundant. Feeding bouts occurred further apart as the distance from shore increased, but there was no corresponding difference in the number of feeding lunges per dive, suggesting the whales were feeding at the same rate throughout their range, but that prey was more dispersed in offshore waters. This may be evidence of two feeding strategies, with spatially aggregated foraging around highly localized, topographically forced upwelling centers nearshore, and more dispersed foraging in larger areas of elevated, but patchy, productivity offshore.
“…Blue whales have been shown to adjust their dive behavior based on the density of prey in the area (Goldbogen et al, 2015;Hazen et al, 2015), so it is possible they encountered prey in insufficient concentrations for them to feed upon. More broadly, males and females of central-place foragers are known to have different sex-based foraging strategies arising from different energetic requirements during reproduction and resulting in differential exploitation of the offshore and coastal environment (Breed et al, 2006;Austin et al, 2019). A similar process could be driving the observed differences between male blue and fin whales.…”
Intermediate-duration archival tags were attached to eight blue whales (Balaenoptera musculus; four females, three males, one of unknown sex), and five fin whales (B. physalus; two females, one male, two of unknown sex) off southern California, USA, in summer 2014 and 2015. Tags logged 1-Hz data from tri-axial accelerometers, magnetometers, and a depth sensor, while acquiring Fastloc GPS locations. Tag attachment duration ranged from 18.3 to 28.9 d for blue whales and 4.9-16.0 d for fin whales, recording 1,030-4,603 dives and 95-3,338 GPS locations per whale across both species. Feeding lunges (identified from accelerometer data) were used to characterize "feeding bouts" (i.e., sequences of feeding dives with <60 min of consecutive non-feeding dives), within-bout behavior, and to examine the spatial distribution of feeding effort. Whales fed near the tagging locations (Point Mugu and San Miguel Island) for up to 7 d before dispersing as far south as Ensenada, Mexico, and north to Cape Mendocino, California. Dispersal within southern California waters differed by sex in both species with males undertaking offshore, circuitous excursions, while females remained more coastal, suggesting that movement patterns on the feeding grounds may not be exclusively related to energy gain. Feeding bout characteristics were similar for both species, with the median bout having 24 dives and lasting 3.3 h for blue whales (n = 242), and 19 dives while lasting 2.7 h for fin whales (n = 59). Bout duration was positively correlated with the number of feeding lunges per dive within a bout for both species, suggesting whales left poor-quality prey patches quickly but fed intensively for up to 34.9 h when prey was abundant. Feeding bouts occurred further apart as the distance from shore increased, but there was no corresponding difference in the number of feeding lunges per dive, suggesting the whales were feeding at the same rate throughout their range, but that prey was more dispersed in offshore waters. This may be evidence of two feeding strategies, with spatially aggregated foraging around highly localized, topographically forced upwelling centers nearshore, and more dispersed foraging in larger areas of elevated, but patchy, productivity offshore.
“…1 ; Latitude: 19.663 °N, Longitude: 80.082 °W; estimated population size in 2017: 2094 breeding adults, [ 46 ]); and 2) beach and cliff locations on Cayman Brac that support a small scattered breeding population of BBs (Fig. 1 ; Latitude: 19.711 °N, Longitude: 79.801 °W; estimated population size in 2017: 146 breeding adults, [ 47 ]). Fig.…”
Background
Social interactions, reproductive demands and intrinsic constraints all influence foraging decisions in animals. Understanding the relative importance of these factors in shaping the way that coexisting species within communities use and partition resources is central to knowledge of ecological and evolutionary processes. However, in marine environments, our understanding of the mechanisms that lead to and allow coexistence is limited, particularly in the tropics.
Methods
Using simultaneous data from a suite of animal-borne data loggers (GPS, depth recorders, immersion and video), dietary samples and stable isotopes, we investigated interspecific and intraspecific differences in foraging of two closely-related seabird species (the red-footed booby and brown booby) from neighbouring colonies on the Cayman Islands in the Caribbean.
Results
The two species employed notably different foraging strategies, with marked spatial segregation, but limited evidence of interspecific dietary partitioning. The larger-bodied brown booby foraged within neritic waters, with the smaller-bodied red-footed booby travelling further offshore. Almost no sex differences were detected in foraging behaviour of red-footed boobies, while male and female brown boobies differed in their habitat use, foraging characteristics and dietary contributions. We suggest that these behavioural differences may relate to size dimorphism and competition: In the small brown booby population (n < 200 individuals), larger females showed a higher propensity to remain in coastal waters where they experienced kleptoparasitic attacks from magnificent frigatebirds, while smaller males that were never kleptoparasitised travelled further offshore, presumably into habitats with lower kleptoparasitic pressure. In weakly dimorphic red-footed boobies, these differences are less pronounced. Instead, density-dependent pressures on their large population (n > 2000 individuals) and avoidance of kleptoparasitism may be more prevalent in driving movements for both sexes.
Conclusions
Our results reveal how, in an environment where opportunities for prey diversification are limited, neighbouring seabird species segregate at-sea, while exhibiting differing degrees of sexual differentiation. While the mechanisms underlying observed patterns remain unclear, our data are consistent with the idea that multiple factors involving both conspecifics and heterospecifics, as well as reproductive pressures, may combine to influence foraging differences in these neighbouring tropical species.
“…Wintering RCPs must prepare for the ensuing breeding period by balancing the demands of long migratory upand-down flights and self-maintenance while functioning within phenotypic, energetic, and geographical constraints. To meet these challenges, Austin et al (2019) reported that species must adapt their foraging behaviors in ways that ultimately optimize both survival and fitness.…”
The present study aimed at recording the time-activity budget and feeding techniques of red-crested pochards (RCPs) to test the hypotheses that feeding techniques were influenced by the sexes and contrasting physical conditions of the habitat. The timeactivity budget was quantified using the scanned sample approach. In this study, the mean sex ratio of the RCPs was recorded as 0.655. Dominant behavior was sleeping or resting (42.8% in February to 47.0% in January), followed by swimming (27.1% in February to 29.8% in December), feeding (10.9% in December to 16.6% in February), and preening (9.0% in January to 12.1% in February). During the diurnal hours, resting was highest in the morning, while swimming and feeding were both highest midday. Climatic factors, such as the maximum and minimum air temperatures, maximum and minimum air temperature differences, and day length, were considered to be influential on the diurnal time activities of the RCPs. Male birds were more frequent divers than the females and the duration of diving was greater in males than in females. However, in shallow water, beak dipping and upending were major foraging techniques in both sexes. The depth of the water played a significant role in the selection of the feeding techniques.
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