Sex-specific Foraging Research Articles

Sexual dimorphism does not translate into foraging or trophic niche partitioning in Peruvian boobies (Sula variegata).

Intraspecific competition can lead to sexual segregation of diets or foraging behaviors in seabirds, and in some species the resulting niche partitioning is facilitated by sexual dimorphism. However, environmental stochasticity can mediate intraspecific competition and thus the extent of sex-based partitioning. The Peruvian booby (Sula variegata) is a sexually dimorphic seabird endemic to the Humboldt Current System (HCS), a highly variable environment due to El Niño Southern Oscillation. To determine the extent of sexual partitioning in this species, we quantified the foraging and trophic niches of breeding Peruvian boobies at Isla Guañape Norte, Peru in two years with different oceanographic conditions and nesting propensity. Morphometrics, GPS-tracked foraging behaviors, diets via regurgitates, and isotopic niches were compared between sexes and years where sample sizes permitted. Although females were larger and in better body condition than males, breeding Peruvian boobies in our study did not exhibit sex-specific foraging or isotopic niche partitioning and had few differences in diet. Anchoveta (Engraulis ringens) dominated diets in both years, reflecting Peruvian boobies' dependence on this prey. Overall, while oceanographic conditions in 2016 were unfavorable enough to reduce nesting propensity, these effects did not qualitatively translate to foraging or dietary niche partitioning between the sexes for those individuals who opted to breed. In combination, our results suggest weak intraspecific competition during our study period, and highlight how the foraging strategies of Peruvian boobies have adapted to the variable environmental conditions found in the HCS.

Females know best: dispersal polymorphism maintained by sex-specific foraging

Females know best: dispersal polymorphism maintained by sex-specific foraging

Phenology and foraging bias contribute to sex-specific foraging patterns in the rare declining butterfly Argynnis idalia idalia.

Variation in pollinator foraging behavior can influence pollination effectiveness, community diversity, and plant-pollinator network structure. Although effects of interspecific variation have been widely documented, studies of intraspecific variation in pollinator foraging are relatively rare. Sex-specific differences in resource use are a strong potential source of intraspecific variation, especially in species where the phenology of males and females differ. Differences may arise from encountering different flowering communities, sex-specific traits, nutritional requirements, or a combination of these factors. We evaluated sex-specific foraging patterns in the eastern regal fritillary butterfly (Argynnis idalia idalia), leveraging a 21-year floral visitation dataset. Because A. i. idalia is protandrous, we determined whether foraging differences were due to divergent phenology by comparing visitation patterns between the entire season with restricted periods of male-female overlap. We quantified nectar carbohydrate and amino acid contents of the most visited plant species and compared those visited more frequently by males versus females. We demonstrate significant differences in visitation patterns between male and female A. i. idalia over two decades. Females visit a greater diversity of species, while dissimilarity in foraging patterns between sexes is persistent and comparable to differences between species. While differences are diminished or absent in some years during periods of male-female overlap, remaining signatures of foraging dissimilarity during implicate mechanisms other than phenology. Nectar of plants visited more by females had greater concentrations of total carbohydrates, glucose, and fructose and individual amino acids than male-associated plants. Further work can test whether nutritional differences are a cause of visitation patterns or consequence, reflecting seasonal shifts in the nutritional landscape encountered by male and female A. i. idalia. We highlight the importance of considering sex-specific foraging patterns when studying interaction networks, and in making conservation management decisions for this at-risk butterfly and other species exhibiting strong intraspecific variation.

Immature wild orangutans acquire relevant ecological knowledge through sex-specific attentional biases during social learning.

As a part of growing up, immature orangutans must acquire vast repertoires of skills and knowledge, a process that takes several years of observational social learning and subsequent practice. Adult female and male orangutans show behavioral differences including sex-specific foraging patterns and male-biased dispersal. We investigated how these differing life trajectories affect social interest and emerging ecological knowledge in immatures. We analyzed 15 years of detailed observational data on social learning, associations, and diet repertoires of 50 immatures (16 females and 34 males), from 2 orangutan populations. Specific to the feeding context, we found sex differences in the development of social interest: Throughout the dependency period, immature females direct most of their social attention at their mothers, whereas immature males show an increasing attentional preference for individuals other than their mothers. When attending to non-mother individuals, males show a significant bias toward immigrant individuals and a trend for a bias toward adult males. In contrast, females preferentially attend to neighboring residents. Accordingly, by the end of the dependency period, immature females show a larger dietary overlap with their mothers than do immature males. These results suggest that immature orangutans show attentional biases through which they learn from individuals with the most relevant ecological knowledge. Diversifying their skills and knowledge likely helps males when they move to a new area. In sum, our findings underline the importance of fine-grained social inputs for the acquisition of ecological knowledge and skills in orangutans and likely in other apes as well.

Foraging niche overlap during chick-rearing in the sexually dimorphic Westland petrel.

Most Procellariform seabirds are pelagic, breed in summer when prey availability peaks, and migrate for winter. They also display a dual foraging strategy (short and long trips) and sex-specific foraging. The Westland petrel Procellaria westlandica, a New Zealand endemic, is one of the rare seabirds breeding in winter. Preliminary findings on this large and sexually dimorphic petrel suggest a foraging behaviour with no evidence of a dual strategy, within a narrow range and with shared areas between sexes. To investigate further this unusual strategy, the present study determined the fine-scale at-sea behaviours (global positioning system and accelerometer data loggers) and trophic niches (stable isotopes in whole blood) of chick-rearing individuals (16 males and 13 females). All individuals foraged on the shelf-slope of the west coast of New Zealand's South Island with short, unimodal trips. Both sexes foraged at similar intensity without temporal, spatial or isotopic niche segregation. These findings suggest the presence of a winter prey resource close to the colony, sufficient to satisfy the nutritional needs of breeding without increasing the foraging effort or intra-specific competition avoidance during winter. Additional data are needed to assess the consistency of foraging niche between the sexes and its reproductive outcomes in view of anticipated environmental changes.

The Allometry of Sexual Dimorphism in Sceloporus formosus (Squamata: Phrynosomatidae)

In many animal species, adult females and males often differ in characteristics other than primary sexual traits. Thus, body size tends to be related to reproductive success through different pathways in females and males, sex-specific foraging or dispersal strategies, and/or adaptations to reduce intersexual trophic competition. As result of these differences, the body size that conveys maximal fitness often differs between the sexes, favoring the evolution of sexual size dimorphism. In this study, we use an allometric approach to evaluate the changes in magnitude of sexual dimorphism in a population of Sceloporus formosus. Allometry refers to the relationships observed between body size and other organismal traits. Natural and sexual selection on morphological traits may modify allometric relationships. Traits under selection can show positive allometry, with slopes steeper than 1 (hyperallometry). We performed allometric major axis regressions of seven morphological traits on the snout–vent length, a standard measure used as a proxy for lizard size. The major axis regressions of female trunk length and width, and male trunk length showed hyperallometric slopes, suggesting that in S. formosus these traits could be under natural selection.

Calf age and sex affect maternal diving behaviour in Shark Bay bottlenose dolphins

Calf age and sex affect maternal diving behaviour in Shark Bay bottlenose dolphins

Sexual segregation in tropical seabirds: drivers of sex-specific foraging in the Brown Booby Sula leucogaster

Sexual segregation in the behaviour, morphology or physiology of breeding seabirds can be related to divergent parental roles, foraging niche partitioning or sex-specific nutritional requirements. Here, we combine GPS tracking, dietary and nutritional analysis to investigate sex-specific foraging of Brown Boobies breeding on Raine Island, Great Barrier Reef, Australia. We observed sex-specific segregation in: (1) foraging location: females undertook longer trips, foraging at more distant locations than males; (2) foraging time: male activity and foraging occurred throughout the day, while female activity and foraging increased from midday to an afternoon peak; and (3) prey type, females mostly consumed flying fish, whereas males consumed equal proportions of flying fish and squid. Brown Booby diets contained five tropical prey species that significantly differed in their nutritional composition (Protein, Lipid and Water, wet mass). Despite this variation we found no differences in the overall nutritional content of prey caught by each sex. The observed sex-specific differences in prey type, location and time of capture are likely driven by a combination of a division of labour, risk partitioning and competition. However, Brown Boobies breeding on Raine Island, and other populations, might flexibly partition foraging niches by sex in response to varying competitive and environmental pressures. In light of such potential foraging dynamism, our inconclusive exploration of nutritional segregation between sexes warrants further investigation in the species.

Sex-specific foraging during parental care in a size-monomorphic seabird, the Australasian Gannet ( Morus serrator )

ABSTRACT Sex differences in foraging behavior are typically studied in size-dimorphic taxa. Data on sex-specific behavior in monomorphic taxa are needed to test theories of reproductive investment. It has been suggested that in seabirds foraging niche separation may be related to decreased intersexual competition for food between cooperating pair-bonded individuals. Alternatively, sex differences in foraging niches may be driven by different nutritional requirements of females associated with the reproductive costs of egg production and oviposition. To assess these possibilities, we studied a size-monomorphic colonial seabird, the Australasian Gannet (Morus serrator) at the Cape Kidnappers gannetry, New Zealand. We recorded maximum dive depths, and distinct diet composition of incubating females as indicated by stable isotopic signatures. Results suggested greater female foraging effort during early times of incubation, indicated by significantly deeper maximum dives. Sex-specific foraging patterns across...

Seasonal Variation in Parental Care Drives Sex-Specific Foraging by a Monomorphic Seabird.

Evidence of sex-specific foraging in monomorphic seabirds is increasing though the underlying mechanisms remain poorly understood. We investigate differential parental care as a mechanism for sex-specific foraging in monomorphic Common Murres (Uria aalge), where the male parent alone provisions the chick after colony departure. Using a combination of geolocation-immersion loggers and stable isotopes, we assess two hypotheses: the reproductive role specialization hypothesis and the energetic constraint hypothesis. We compare the foraging behavior of females (n = 15) and males (n = 9) during bi-parental at the colony, post-fledging male-only parental care and winter when parental care is absent. As predicted by the reproductive role specialization hypothesis, we found evidence of sex-specific foraging during post-fledging only, the stage with the greatest divergence in parental care roles. Single-parenting males spent almost twice as much time diving per day and foraged at lower quality prey patches relative to independent females. This implies a potential energetic constraint for males during the estimated 62.8 ± 8.9 days of offspring dependence at sea. Contrary to the predictions of the energetic constraint hypothesis, we found no evidence of sex-specific foraging during biparental care, suggesting that male parents did not forage for their own benefit before colony departure in anticipation of post-fledging energy constraints. We hypothesize that unpredictable prey conditions at Newfoundland colonies in recent years may limit male parental ability to allocate additional time and energy to self-feeding during biparental care, without compromising chick survival. Our findings support differential parental care as a mechanism for sex-specific foraging in monomorphic murres, and highlight the need to consider ecological context in the interpretation of sex-specific foraging behavior.

Sex-specific foraging behavior in response to fishing activities in a threatened seabird.

Some seabird species have learnt to efficiently exploit fishing discards from trawling activities. However, a discard ban has been proposed as necessary in Europe to ensure the sustainability of the seas. It is of crucial importance for the management and conservation purposes to study the potential consequences of a discard ban on the foraging ecology of threatened seabirds. We assessed the influence of fishing activities on the feeding habits of 22 male and 15 female Audouin's gulls (Larus audouinii) from the Ebro Delta (Mediterranean Sea) during the breeding period using GPS loggers together with Stable Isotope Analysis (SIA), which provided new insights into their foraging behavior and trophic ecology, respectively. GPS data revealed different sex-specific foraging patterns between workdays and weekends. Females were highly consistent in that they foraged at sea throughout the week even though discarding stops at weekends. In contrast, males switched from foraging at sea during the week (when discards are produced) to an increased use of rice field habitats at weekends (when fishermen do not work). This sex-specific foraging behavior could be related to specific nutritional requirements associated with previous egg production, an energetically demanding period for females. However, on a broader time scale integrated by the SIA, both sexes showed a high degree of individual specialization in their trophic ecology. The need to obtain detailed information on the dependence and response of seabirds to fishing activities is crucial in conservation sciences. In this regard, sex-specific foraging behavior in relation to fisheries has been overlooked, despite the ecological and conservation implications. For instance, this situation may lead to sex differentiation in bycatch mortality in longlines when trawlers do not operate. Moreover, any new fisheries policy will need to be implemented gradually to facilitate the adaptation of a specialized species to a discard ban scenario.

Condition factor and diet of the catfish Loricariichthys castaneus (Castelnau, 1855): gender differences in three tropical reservoirs

Condition factor and diet of male and female of Loricariichthys castaneus were studied in three tropical reservoirs in which it is the most abundant species of fish. The females had higher condition factors than males in all three environments, but their diet differed from males only in the best-preserved ecosystem (Lajes Reservoir). Loricariichthys castaneus was considered as detritivorous-omnivorous. Starvation during breeding possibly contributes to a decrease of condition factor in males. By studying the gut content, sex-specific foraging and the influence of the diet importance in relation to the available food items in the three reservoirs were analyzed.

Sex-specific foraging behaviour in northern gannets Morus bassanus: incidence and implications

Sexual segregation in foraging and migratory behaviour is widespread among sexu- ally dimorphic marine vertebrates. It has also been described for a number of monomorphic spe- cies, yet the underlying mechanisms are poorly understood. We examined variation among years, seasons and age-classes in sex-specific foraging and over-wintering behaviour in the northern gannet Morus bassanus , a species with slight sexual dimorphism. Our results revealed consistent sexual differences in the stable isotope ratios of breeding birds: over 3 different breeding periods, adult females consistently consumed prey with significantly lower δ 13 C and δ 15 N values than adult males. Additionally, GPS tracking data showed that breeding females foraged further offshore than breeding males (a result consistent with the δ 13 C data), and the home ranges of the 2 sexes were distinct. Analyses of stable isotope ratios using a Bayesian mixing model (SIAR) revealed that breeding males consumed a higher proportion of fishery discards than females. Analysis of stable isotope ratios in red blood cells of immature gannets (aged 2 to 4) indicated that sexual seg- regation was not present in this age-class. Although sample sizes were small and statistical power correspondingly low, analysis of geolocator data and of stable isotope ratios in winter-grown flight feathers revealed no clear evidence of sexual segregation during the non-breeding period. Together these results provide detailed insight into sex-specific behaviour in gannets throughout the annual cycle, and although the mechanisms remain unclear they are unlikely to be explained by slight differences in size.

Hunting and Gathering

Among human foragers, males and females target different foods and share them. Some view this division of labor as a cooperative enterprise to maximize household benefits; others question men's foraging goals. Women tend to target reliable foods. Men tend to target energy-dense foods that are difficult to acquire and are shared widely outside the household, perhaps to advertise their phenotypic quality to potential mates and allies via a costly, and thus hard to fake, signal. An analysis of variation in sex-specific foraging was conducted to investigate its causes and origins. There is less division of labor in less seasonal, more productive habitats where males do more gathering. This suggests males respond more as optimal foragers than maximal signalers. The division of labor likely evolved after pair bonds, and after gathering technology became efficient enough to provision others, allowing males to specialize in foods with the greatest trade value with females.

Unusual fatty acid biomarkers reveal age- and sex-specific foraging in polar bears (Ursus maritimus)

We used fatty acid (FA) biomarkers in a novel approach to study the foraging habits of a top predator. We tested the hypothesis that non-methylene-interrupted FA (NMI FA), synthesized by benthic molluscs, are transferred via pinnipeds to polar bears ( Ursus maritimus Phipps, 1774) at the top of the arctic marine food web. Among eight species of marine mammals preyed upon by polar bears, NMI FA were prevalent only in benthic-feeding bearded seals ( Erignathus barbatus (Erxleben, 1777)) and Atlantic walruses ( Odobenus rosmarus rosmarus (L., 1758)). These two prey species differed in their relative proportions of NMI FA — 22:2Δ7,15 was almost exclusive to bearded seals, whereas 20:2Δ5,11 was most abundant in Atlantic walruses. Six different NMI FA were identified in polar bears. Trends in individual NMI FA showed that large, adult male polar bears were the primary predators of bearded seals and Atlantic walruses. These findings were confirmed through quantitative FA signature analysis (QFASA) using an entirely different set of FA. In addition to corroborating the accuracy of QFASA diet estimates, these results indicate that individual NMI FA can provide specific information on polar bear foraging and therefore provide insights into the bottom–up effects of environmental change in arctic ecosystems.

Sex‐Specific Life History Tactics and Risk‐Taking in Coho Salmon

Differences in size and abundance between males and female at sexual maturity are common in vertebrates. Evolutionary explanations for these differences generally assume a consistent pattern within a species. Among Pacific salmon (Oncorhynchus spp.) and coho salmon (O. kisutch) in particular, however, sexual size dimorphism and sex ratio are not consistent among or within populations, making extant explanations unsatisfactory. In this paper we describe the variation size dimorphism and sex ratio within and among coho salmon populations and propose a model to account for this variation. Our data consist of a 16—yr study of coho salmon in carnation Creek, British Columbia, and shorter term studies of 30 other coho populations ranging from California to Alaska. Among mature coho salmon in Carnation Creek males outnumbered females but females were larger, and the male/female sex ratio varied directly with the female/male size ratio. Mean female size was constant over 16 yr, while male size varied inversely with the male/female sex ratio. Females apparently had higher mortality rates than males, and the difference in mortality rates appeared to increase as the animals neared maturity. Sex— and size—ratio data from other coho salmon populations indicate that there are two general population types. In one type males outnumber females, and females are larger at maturity. In the other type the sexes are equally abundant and equal in size. We propose that the range of size for successful reproduction in coho salmon is set by conditions in the breeding environment, and that the range differs for males and females because of the different roles that the sexes play in reproduction. The sex—specific constraints on reproductive size lead to sex—specific foraging strategies and risk—taking. Interpopulation differences in size and sex ratio are determined by differences in physical characteristics of the breeding environment, spawning population density, and the relative riskiness of ocean nursery areas. Within populations, variation is determined by the interaction of sex—specific foraging strategies with interannual variation in ocean feeding conditions and predator abundance.

Ptilochronology: Feather Growth Bars as Indicators of Nutritional Status

Ptilochronology: Feather Growth Bars as Indicators of Nutritional Status