Feeding Effort Research Articles

Do Male Pied Flycatchers (Ficedula hypoleuca) Adjust Their Feeding Effort According to Egg Colour?

The colour of blue-green bird eggs has been hypothesized to signal female quality to attending males, who may adjust their level of investment in the brood accordingly. The hypothesis has gained support in studies of Spanish pied flycatchers Ficedula hypoleuca. We performed a cross-fostering experiment in a Norwegian population of pied flycatchers to provide an independent test of the sexually selected egg colour hypothesis in this species. Egg colour was not significantly correlated with estimates of female quality (clutch size, average egg volume, first egg laying date and feeding rate). There was a significant decrease in chroma and increase in brightness and egg volume during the laying sequence, with some marked differences between six-egg and seven-egg clutches that might reflect differences in female quality. However, we found no significant influence of egg colour (foster or original clutch) on male feeding rate or offspring viability (hatching success, average mass and fledging success) and no significant difference in feeding rate for males with six-egg and seven-egg foster or original clutches. We conclude that Norwegian male pied flycatchers do not use egg colour as a cue to female quality, thus questioning the generality of previous support for the sexually selected egg colour hypothesis from this species.

Endogenous testosterone is not associated with the trade-off between paternal and mating effort

Males may face a trade-off between caring for offspring and pursuing additional matings. In birds, the androgen testosterone has been suggested to be a key proximate mediator in this trade-off for several reasons. At the population level, high testosterone is typically associated with the period of intense male–male competition over females, whereas low testosterone is associated with the period of paternal care. In addition, males with experimentally elevated testosterone during provisioning feed their young at a lower rate than control males. Nearly all studies observing these patterns, however, ignore the tremendous variation in endogenous testosterone concentration that exists within a population of males, even during the same breeding stage. Because selection acts at the level of individual, this variation has to be taken into account when studying proximate mechanisms mediating the paternal and mating effort trade-off. Studying barn swallows we here show that, within males, testosterone concentrations were not higher around the fertile period of the social mate than during nestling feeding. More importantly, 30% of males showed no decrease in testosterone concentration between these 2 periods. Further, male feeding effort was not related to testosterone concentration during feeding. These results indicate that, at least in barn swallows, endogenous testosterone is not a key mediator in the trade-off between paternal effort and mating effort. Our results also stress that to understand how selection has shaped temporal testosterone profiles and action, it is crucial to study the relationship between testosterone and traits contributing to fitness at the level of the individual. Key words: barn swallow, endogenous testosterone, extrapair, mating effort, nestling feeding, paternal effort. [Behav Ecol]

Feeding Effort of Male Tawny OwlsStrix alucoFollows a Fixed Schedule: A Field Experiment in the Early Nestling Period

The ‘fixed schedule hypothesis’ proposes that parental investment is independent of offspring needs in order to maximize adult survival or to prevent reduced future fecundity. We tested this hypothesis on Tawny Owls Strix aluco by experimental manipulation of brood size. We measured the call frequency of begging chicks, feeding frequency of males, overnight weight gain of nestlings and parental body condition in reduced or enlarged broods, and in control broods. In reduced or enlarged broods nestling begging calls reflected the respective decrease or increase in demand, but the frequency with which the males fed did not differ between the reduced and enlarged broods. Consequently, chicks gained body weight more rapidly in reduced broods, whereas those in enlarged broods grew more slowly. Male body weight did not change during the early nestling period when they delivered food to reduced or enlarged broods, but the condition of females worsened in the enlarged broods. As the males did not increase the feeding frequency in the enlarged broods, the females were under pressure to pass on more of the prey to nestlings begging in these broods. Male Tawny Owls regulated their feeding effort according to a fixed schedule, independently of the chicks' needs, to maintain their body condition. Nevertheless, the females whose condition deteriorated during the feeding of enlarged broods did not stop brooding earlier, nor did they suffer mortality in the breeding period.

Seasonal Variations in the Diet and Feeding Effort of Two Groups of Howlers in Different Sized Forest Fragments

Little is known about how resource limitation affects the feeding ecology of primates in forest fragments. Here, we describe seasonal variation in the diet and feeding effort of 2 groups (RH and RC3) of howlers (Alouatta palliata mexicana) living in different sized forest fragments in Los Tuxtlas, Mexico. The RH group, which lived in a larger and more preserved forest fragment, with a higher availability of fruit and Ficus trees, had a higher and more constant consumption of fruit throughout the study year. Moreover, this group fed from larger food sources, i.e., trees, lianas, and shrubs, and spent more time feeding from each food source. The feeding effort, defined as the time spent feeding and traveling divided by time spent resting, of the RH group was also significantly lower and more stable than that of the RC3 group throughout the study year. As feeding effort has been positively related to stress in primates, such increases in feeding effort could have negative consequences for howlers in small or degraded forest fragments. Our study suggests that habitat characteristics interact with plant seasonality to determine the diet and feeding effort of howlers in forest fragments and that groups living in small and degraded forest fragments may be particularly vulnerable to years of low fruit production.

Co-variation between autotrophy and heterotrophy in the Mediterranean coral Cladocora caespitosa

This study quantifies the relative contributions of autotrophy and heterotrophy to the energy budget of the temperate scleractinian species Cladocora caespitosa Linnaeus 1767. Colonies were incubated under different light and feeding regimes, and changes in carbon acquisition through photosynthesis and feeding were measured during a 2-month time period. This approach allowed us to quantify the rate at which adjustments to physiology occurred, as well as the magnitude of up- or downregulation of both feeding modes. In addition, we explored how shifts in carbon acquisition mode influenced tissue biomass (protein content), energy stores (lipid content) and colony growth (calcification). Increases in feeding capacity during prolonged exposure to darkness were correlated with decreases in photosynthetic capacity. However, feeding effort did not decrease when photosynthesis was high. In fact, feeding was maximal under high light conditions when food was not available. During starvation, colonies used their lipid stores to partially meet their metabolic requirements. Colonies kept in low light used nutrients from feeding to supplement calcification, whereas those kept at high light converted carbon from feeding into tissue biomass. This work provides the first estimates of rates of adjustment of heterotrophic feeding capacity in a Mediterranean scleractinian coral. For the study species, flexibility in carbon acquisition through heterotrophy was approximately equal to flexibility in photosynthesis both in magnitude and in the rate at which physiological adjustments occurred. The ability to alter feeding effort rapidly and strongly may explain the wide depth distribution of C. caespitosa, and its ability to survive in turbid coastal waters where light is often limited.

Fecal glucocorticoids as indicators of metabolic stress in female Sykes' monkeys (C ercopithecus mitis albogularis)

Because of their mediating role in the stress response and potential effects on fitness, glucocorticoid (GC) hormones are increasingly used to assess the physiological costs of environmental and behavioral variation among wild vertebrates. Identifying the proximate causes of GC variation, however, is complicated by simultaneous exposure to multiple potentially stressful stimuli. Here, we use data from a partially provisioned social group of Sykes' monkeys to evaluate the effects of potential psychological and metabolic stressors on temporal and individual variation in fecal GC (fGC) excretion among 11 adult females. Despite high rates of agonism over provisioned foods fGCs declined during periods of high provisioning frequency when fruit availability was dominated by neem ( Azadirachta indica), an item requiring great feeding effort. Provisioned foods did not prevent fGC increases when availability of the most preferred main fruit item, tamarind ( Tamarindus indica), declined drastically. Although rank-related differences in access to provisioned foods and rates of agonism did not lead to an overall effect of rank on fGCs, low-ranking females excreted more fGCs than high-ranking females during a period of high provisioning intensity and low fruit availability. The emergence of this rank effect was associated with elevated feeding effort in all females, a greater access to provisioned items by high-ranking females, and a higher proportion of time spent moving in low-ranking females. Our findings suggest that metabolic stressors were the primary determinants of both temporal and individual variation in fGCs, indicating potential fitness benefits for high-ranking females when food availability is limited.

Experimental assessment of the feeding effort of three scleractinian coral species during a thermal stress: Effect on the rates of photosynthesis

This study aimed at investigating changes in feeding rates of three scleractinian coral species (Stylophora pistillata, Turbinaria reniformis and Galaxea fascicularis) between control (26°C) and short-term stress conditions (31°C), and to assess the effect of feeding on the photosynthetic efficiency of the corals. Feeding rates varied according to the feeding effort of the corals, itself depending on the environmental conditions. Indeed, S. pistillata significantly decreased its feeding rates at 31°C, while rates of T. reniformis and G. fascicularis were increased between 26 and 31°C. Independently of the feeding rates, food supply helped in preventing damage to the photosynthetic apparatus of the zooxanthellae. Indeed, starved corals from the three species showed significant decrease in both the electron transport rates and in the photosynthetic rates, following a loss in the amount of chlorophyll and experiencing photoinhibition of the photosystem II. However, no bleaching was observed in heated fed corals, with no decrease in their photosynthetic efficiency or performance.

Sex Differences in the Rate of Food Provisioning to Nestlings Red-Breasted Flycatchers (Ficedula parva)

Parental care is one of the crucial factors affecting breeding success in birds. The level of parent investment can differ between males and females. We studied the sex-specific nestling-feeding effort by parents of the red-breasted flycatcher. Our study was carried out in the old-growth oak—lime—hornbeam stands in the Białowieża National Park (NE Poland). The frequency of nestling-feeding and relative nestling-feeding effort (number of visits by male or female expressed a percentage of all visits by both sexes at the nest) depended on sex of parents and age of nestlings but not on their number. Both sexes increased their feeding frequency as the nestlings became older. Sex differences in nestling-feeding have been found in a number of biparental-care bird species. There are many hypotheses to explain this phenomenon. In the red-breasted flycatcher, the most likely reason for differences in feeding efforts are differences in roles the parents play at different stages of brood develompent.

Consequences of ‘load‐lightening’ for future indirect fitness gains by helpers in a cooperatively breeding bird

1. Helpers that invest energy in provisioning the offspring of related individuals stand to gain indirect fitness benefits from doing so. First, if the helper's effort is additional to that of the parents (additive) the productivity of the current breeding attempt can be increased. Secondly, if the parents reduce their workload (compensation) this can result in future indirect fitness gains to the helper via increased breeder survival; termed 'load-lightening'. 2. Long-tailed tits (Aegithalos caudatus) have a cooperative breeding system in which helpers assist kin and parents exhibit both additive and compensatory reactions in the presence of helpers. Offspring from helped nests are heavier and more likely to recruit into the breeding population, thus helpers gain indirect fitness benefits from increasing the productivity of the current breeding attempt. Despite breeders' reduction of feeding effort in the presence of helpers, previous investigations found no subsequent increase in breeder survival. 3. The aim of this study was to test the hypothesis that load-lightening resulted in indirect fitness benefits for helpers. We used data from a 14-year study to investigate the provisioning rate, survival and future fecundity of male and female long-tailed tits that did and did not receive help at the nest. 4. We found an asymmetrical response to the presence of helpers at large brood sizes. Males reduced their feeding rate more than females, and this differential response was reflected in a significant increase in male survival when provisioning large broods assisted by helpers. We found no evidence of any increase in future fecundity for helped breeders. 5. The finding that males reduce their provisioning rate in the presence of helpers (at large brood sizes) to a greater degree than females, and that this is reflected in an increase in survival rate for males only, implies that the survival increase is caused by the reduction in work-rate rather than a non-specific benefit of a larger group size. 6. The marginal benefits of help for breeder survival are likely to be more difficult to identify than the increased productivity at helped nests, but should not be overlooked when investigating the potential indirect fitness gains that supernumeraries can accrue by helping.

Marine no-take zone rapidly benefits endangered penguin

No-take zones may protect populations of targeted marine species and restore the integrity of marine ecosystems, but it is unclear whether they benefit top predators that rely on mobile pelagic fishes. In South Africa, foraging effort of breeding African penguins decreased by 30 per cent within three months of closing a 20 km zone to the competing purse-seine fisheries around their largest colony. After the fishing ban, most of the penguins from this island had shifted their feeding effort inside the closed area. Birds breeding at another colony situated 50 km away, whose fishing grounds remained open to fishing, increased their foraging effort during the same period. This demonstrates the immediate benefit of a relatively small no-take zone for a marine top predator relying on pelagic prey. Selecting such small protected areas may be an important first conservation step, minimizing stakeholder conflicts and easing compliance, while ensuring benefit for the ecosystems within these habitats.

Family size and sex-specific parental effort in black-legged kittiwakes

Summary Clutch and brood reduction is widespread in birds and is mainly caused by lower parental effort during incubation or chick rearing. In black-legged kittiwakes Rissa tridactyla, early chick rearing seems to be more costly for females than males. We, thus, hypothesized that energetically constrained females may be responsible for the low feeding delivery causing brood-reduction. Furthermore, as previous studies have experimentally shown that only females reduce their feeding effort after brood-reduction, we hypothesized that females should decrease their investment after natural clutch or brood reduction. For three consecutive years, we observed parental attendance and feeding behaviour during chick rearing in pairs that hatched only one of their eggs, lost one of their two hatchlings or raised two chicks. We found that in pairs that lost one egg, parents behaved as predicted, with females showing low feeding effort. Furthermore, we found that before brood-reduction, females, but not males delivered less food to their chicks than parents that raised two chicks, and that A-chicks were more aggressive when females delivered less food to them. These results suggest that females may be responsible for brood-reduction. However, after brood-reduction, contrary to what was expected, females did not show lower feeding rate than females raising two chicks. We discuss two non-exclusive potential mechanisms at the origin of this result, namely that brood-reduction may be due to (i) low quality females that are not able to feed their two chicks enough or to (ii) females that adaptively restrained their feeding effort to maximize their residual reproductive value.

Patch area, substrate depth, and richness affect giving‐up densities: a test with mourning doves and cottontail rabbits

We compared the foraging behavior of mourning doves Zenaida macroura and cottontail rabbits Sylvilagus floridanus in patches that varied in initial food abundance, surface area and substrate depth. We measured giving‐up densities (GUD), food harvest and proportion of food harvested to investigate their ability to respond to characteristics of resource patches. GUDs have been analyzed in three ways: grams of per patch, grams per unit surface area (GUDAREA), and grams per unit volume of sand (GUDVOL).Mourning doves and cottontails exhibited similar responses to resource density and sand depth. Both foragers detected and responded to variation in initial food abundance. The proportion of food harvested from a patch increased from 40.7, 43.8 to 48.3% (for the doves) and 34.9, 35.8 to 38.4% (for the rabbits) in patches of low, medium and high initial food abundance, respectively. Deeper substrates reduced the foragers’ encounter probability with food, decreased patch quality and resulted in higher GUDs (60% higher in the deepest relative to shallowest substrate) and lower harvests. A significant interaction between initial food abundance and substrate depth showed that both species were willing to dig deeper in patches with higher resource density. Patch size (surface area) had no effect on food harvest or the proportion of food harvested. Consequently, GUDAREA and GUDVOL increased in patches with a smaller surface area. Smaller patches appeared to hamper the dove's and cottontail's movement across the surface.Our results revealed that mourning doves and cottontails forage under imperfect information. Both species were able to respond to patch properties by biasing their feeding efforts toward rich and easy opportunities, however, mourning doves were more efficient at food harvesting.The interaction of patch area, volume and food abundance directly influenced food harvest. Such resource characters occur under natural situations where food varies in abundance, area of distribution, and accessibility.

Male spotless starlings adjust feeding effort based on egg spots revealing ectoparasite load

Parents may vary their parental behaviour and investment in reproduction in response to parasite-induced changes in the fitness prospects of their offspring. Thus, parents may use the physical condition of their offspring, or any other trait related to parasite load, to adjust parental effort. The immaculate eggs of the spotless starling, Sturnus unicolor, often become densely spotted owing to the activity of the ectoparasite carnid fly Carnus hemapterus. Spot density anticipates the intensity of fly infestation suffered by nestlings and, therefore, may serve as a cue for parents to adjust reproductive investment. By cleaning spots produced by C. hemapterus on eggs of spotless starlings, we manipulated the parasite's traces revealing its presence in broods of starlings, without modifying the level of infestation, to test whether parents use these signals to adjust reproductive effort. We found support for the hypothetical negative effect of Carnus flies since nestlings raised in nests with a higher fly load had lower body mass. The experimental egg cleaning during incubation did not change the intensity of carnid fly infestation during nestling development. However, it had a significant positive influence on paternal but not maternal effort. Our experimental results support the idea that spotless starling males adjust their effort in response to their perception of the fitness prospects of their nestlings as indirectly estimated by traces of parasites on the eggshells. As far as we know, this is the first evidence of the use of parasite traces to infer risk of parasitic infestation by animal hosts.

Time budgets of Tibetan eared pheasants during the non-breeding season in an alpine scrub habitat

Abstract Time allocations of the group-living Tibetan eared pheasants Crossoptilon harmani with and without supplementary food were investigated by full-day sampling from winter through spring in an alpine scrub zone, south Tibet. At a flock scale, both the different food-supply flocks displayed similar daily patterns of activity, foraging in the morning and evening, and resting around midday. In terms of individual activity, either foraging or resting was highly synchronous with the flock’s. Non-provisioned birds spent more time feeding and less resting in midwinter than in late autumn. In early spring as climates became warmer and day longer, however, non-provisioned birds did not decrease their feeding efforts significantly but the provisioned birds did. Across the non-breeding seasons, the provisioned birds (relying on nutrition-rich artificial food) devoted less time to feeding and more to resting than did the non-provisioned ones (relying on nutrition-poor plant roots). Multivariate analysis showed increased food supply and ambient temperature resulted in a reduced foraging effort. However, the fact that the non-provisioned birds can save daily time for resting even in the cold short-day length mid-winter indicated that they faced no energetic constraint. Thus, protecting shelter vegetation rather than providing extra food is suggested to be important for long-term survival of the endangered galliform birds.

Families on the spot: sexual signals influence parent–offspring interactions

In 1950, Tinbergen described the elicitation of offspring begging by the red spot on the bill of parent gulls, and this became a model system for behavioural studies. Current knowledge on colour traits suggests they can act as sexual signals revealing individual quality. However, sexual signals have never been studied simultaneously in relationship to parent-offspring and sexual conflicts. We manipulated the red-spot size in one member of yellow-legged gull pairs and observed their partners' feeding efforts in relationship to offspring begging. In the enlarged-spot group, partners doubled their effort compared with the other groups. Furthermore, in the reduced-spot group, partners provided food in relationship to offspring begging, contrasting with the fixed effort of the partners of enlarged-spot gulls. Manipulated gulls, independently of treatment, provided food in relationship to chicks begging only when the partner's investment was low, and performed a fixed effort when the partner's contribution was high. Results demonstrate that the red spot in yellow-legged gulls functions as a sexual signal and indicate that parental rules are plastic, depending on the information on offer. Previous evidence and this study indicate that this signal is used by all family members to adjust decision rules. The incorporation of sexual signals in parent-offspring interactions can be crucial in understanding intra-familial conflicts.

Do Tengmalm’s Owls alter parental feeding effort under varying conditions of main prey availability?

We studied the diet composition and behavioural responses to variable food conditions in Tengmalm’s Owls (Aegolius funereus). The abundance of main prey (voles and mice) of owls was higher in the Ore Mountains, Czech Republic, than in the Kauhava region, Finland. We monitored nests continuously by a camera system to estimate the feeding frequency and to identify prey items provided to nestlings. We recorded 990 prey deliveries at six nests in the Ore Mountains and 1,679 prey deliveries at nine nests in the Kauhava region. Mice (Apodemus) and voles (Microtus and Clethrionomys) were the main foods of owls in the Ore Mountains, whereas voles (Clethrionomys and Microtus) and shrews (Sorex) were the main foods in the Kauhava region. In consequence, on average smaller prey items were brought to nestlings at the Finnish site. However, both absolute and relative (per one nestling) feeding frequency was higher in the Kauhava region, and the biomass available to individual nestlings did not differ between the two areas. Moreover, the Finnish and Czech pairs produced about the same number of fledglings. Our results suggest that male owls are able to maintain the amount of food required for chicks by switching to alternative prey, and to increase their prey delivery rates under conditions of reduced abundance of main food.

Do free-ranging domestic goats show ‘landscapes of fear’? Patch use in response to habitat features and predator cues

One factor that influences foraging is predation risk. As a result, herbivores may not use landscapes uniformly due to spatial differences in perceived predation risk. Wild herbivores forage across these ‘landscapes of fear’; however, the extent to which domestic herbivores consider them is generally unknown. Using a grid of artificial food patches and measuring giving up densities (GUDs), we mapped landscapes of fear of free-ranging domestic goats on three substrates. In the first experiment, we related GUDs to landscape variables. Goats preferred feeding in open ground with firm substrate compared to a sandy riverbed or a rocky hillside. We suggest that differences relate to escape potential and the occurrence of ambush sites. Landscape variables that influenced feeding effort were patch visibility and plants next to a patch. In a second experiment, we increased predation risk by adding predator dung and urine into the habitats. In response, feeding effort declined across all three habitats. Furthermore, goats only responded to patch visibility and not plants next to the patches. Better sightlines increase predator detection and allow individuals to see group members. Our results indicate that predation risk influences the extent to which free-ranging domestic herbivores utilise landscapes.

Diet, growth and early survival of Atlantic Puffin (Fratercula arctica) chicks in North Norway

Atlantic Puffin (Fratercula arctica) chick growth, diet, feeding rate and early survival and adult body condition were quantified on Hornøya, North Norway in 2002 and 2003 after a long-term change in diet from large Capelin (Mallotus villosus) and Sand Lance (Ammodytes spp.) in the early 1980s to smaller, poorer quality gadids, Sand Lance and Herring (Clupea harengus). The results were compared with data collected in 1980-1982, when feeding conditions were considered very favourable. Chick growth was similar in both periods. The breeding adults compensated for reduced food quality by increasing the feeding frequency, such that the chicks received the same amount of fish (g d-1 and kJ d-1) or even more in 2002-2003. This increase in activity did not, however, result in a decline in adult body mass, suggesting that prey were abundant close to the colony and that the parents did not suffer from the apparent increased feeding effort.

A junk-food hypothesis for gannets feeding on fishery waste

Worldwide fisheries generate large volumes of fishery waste and it is often assumed that this additional food is beneficial to populations of marine top-predators. We challenge this concept via a detailed study of foraging Cape gannets Morus capensis and of their feeding environment in the Benguela upwelling zone. The natural prey of Cape gannets (pelagic fishes) is depleted and birds now feed extensively on fishery wastes. These are beneficial to non-breeding birds, which show reduced feeding effort and high survival. By contrast, breeding gannets double their diving effort in an attempt to provision their chicks predominantly with high-quality, live pelagic fishes. Owing to a scarcity of this resource, they fail and most chicks die. Our study supports the junk-food hypothesis for Cape gannets since it shows that non-breeding birds can survive when complementing their diet with fishery wastes, but that they struggle to reproduce if live prey is scarce. This is due to the negative impact of low-quality fishery wastes on the growth patterns of gannet chicks. Marine management policies should not assume that fishery waste is generally beneficial to scavenging seabirds and that an abundance of this artificial resource will automatically inflate their populations.

INVESTMENT IN NESTING ACTIVITIES AND PATTERNS OF EXTRA- AND WITHIN-GROUP GENETIC PATERNITY IN A COOPERATIVELY BREEDING BIRD

Individuals are predicted to direct aid-giving behaviors preferentially to kin. In this study, we examined patterns of investment in nesting activities and compared them to genetic paternity across a three-year period (1994–1996) in cooperatively breeding Brown Jays (Cyanocorax morio) in Monteverde, Costa Rica. Brown Jays live in large, territorial groups (mean = 10 individuals) that usually contain a single primary nesting female, her social mate (consort), and helpers of both sexes. Consorts were identified in most but not all nesting female-years; the consort–breeding female relationship was a stable one that often persisted across years, and consorts spent more time with the breeding females than did any other group males during nest building and egg laying. At an individual level, helpers invested little time in the nest area or feeding effort during the prenestling stages, although they provided the majority of feedings (90%) to the breeding female. The breeding pair spent more time in the nest area and had higher nestling feeding rates than the helpers. Consorts did not reduce their investment in nestling feeding in cases where they had not obtained paternity. Within-group extra-pair fathers, on the other hand, tended to provision nestlings less than did other nonbreeding males and were very rarely seen in the nesting areas. Extra-group fathers provided no nestling care. Brown Jay consorts appear to invest less in nesting activities compared to other well-studied New World jays. These findings suggest that mate guarding may be ineffective for consorts, and that both consorts and helper males may invest little in nesting activities because they are pursing mating or dispersal opportunities outside their social groups.