Habitat quality, nestling diet, and provisioning behaviour in great tits Parus major

Variation in early nutrition is often a strong predictor of offspring condition and fitness. In the case of woodland passerine birds, nestling diet is determined by the spatiotemporal distribution of prey items such as caterpillars during the nestling period, and is usually quantified as differences in provisioning behaviour between habitats. However, the habitat level does not account for variation between individual territories, the level at which competition and selection are assumed to operate. Here we use nestbox cameras and Radio Frequency Identification technology (RFID) to simultaneously assess variation in both nestling diet (components) and provisioning rates (quantity) among a sample (n=22) of different quality great tit Parus major territories selected from a larger breeding population (n=310 fledged broods) in a single year. Caterpillars were by far the most numerous item provisioned to nestlings (mean=75% of prey items), as expected given the known importance of this food source for this species. Broods raised close to an oak tree, or far from the woodland edge, were provisioned the highest proportion of caterpillars. Provisioning rates declined seasonally and there was a weak association between low provisioning rates and caterpillar rich diets. During the first week of the nestling stage, nestling condition was unrelated to the proportion of caterpillars in the diet, provisioning rates and oak proximity. Condition at fledging was slightly improved in broods fed a higher proportion of caterpillars in the diet and in broods raised close to an oak tree. However, in our data early breeding was the only predictor of recruitment success, although power was low for this test. Analyses of long‐term data (41 years) from the same population confirmed a relationship between oak proximity and fledgling mass, but not recruitment success. Our results suggest that territory level environmental variation can affect offspring condition, probably through observed changes in nestling diet, but that such variation does not necessarily produce discernable effects on offspring fitness.     

Maternal investment in a bee species with facultative nest guarding and males heavier than females

1. Maternal investment can be influenced by several factors, especially maternal quality and possibilities for future reproduction. Mass provisioning Hymenoptera are an excellent group for measuring maternal investment because mothers distribute food sources to each brood cell for each offspring separately. Generally in aculeate Hymenoptera, larger females produce larger offspring and invest more in female offspring than in male offspring. 2. This study investigated patterns of maternal investment in Ceratina chalcites, which has an uncommon type of sexual size dimorphism in Hymenoptera: on average, males are heavier than females. It was found that larger females produce a significantly higher proportion of male offspring, as males are the costlier sex in this species. 3. Facultative nest guarding by females was observed. Females can guard offspring until adulthood, as is typical for bees of genus Ceratina (34.43% of nests); however, in the majority of cases (65.56% of nests), females plug and abandon the nest. Significant differences were found in the amount of investment between guarded and unguarded nests. Guarded nests had a greater number of provisioned brood cells and a higher proportion of male offspring. It is suggested that mothers have two facultative strategies – either she makes a large investment in the offspring of one nest or she abandons the first nest and carries out a second nesting elsewhere.     

Females of the European beewolf preserve their honeybee prey against competing fungi

1. Females of the European beewolf Philanthus triangulum (Hymenoptera, Sphecidae) provision brood cells with paralysed honeybees as larval food. Because brood cells are located in warm, humid locations there is a high risk of microbial decomposition of the provisions. Low incidence of fungus infestation (Aspergillus sp.) in nests in the field suggested the presence of an anti‐fungal adaptation. 2. To test whether the paralysis caused the protection from fungus infestation, the timing of fungus growth on bees that were freeze‐killed, paralysed but not provisioned, and provisioned regularly by beewolf females was determined. Fungus growth was first detected on freeze‐killed bees, followed by paralysed but not provisioned bees. By contrast, fungus growth on provisioned bees was delayed greatly or even absent. Thus, paralysis alone is much less efficient in delaying fungus growth than is regular provisioning. 3. Observations of beewolves in their nests revealed that females lick the body surface of their prey very thoroughly during the period of excavation of the brood cell. 4. To separate the effect of a possible anti‐fungal property of the brood cell and the licking of the bees, a second experiment was conducted. Timing of fungus growth on paralysed bees did not differ between artificial and original brood cells. By contrast, fungus growth on bees that had been provisioned by a female but were transferred to artificial brood cells was delayed significantly. Thus, the treatment of the bees by the female wasp but not the brood cell caused the delay in fungus growth. 5. Beewolf females most probably apply anti‐fungal chemicals to the cuticle of their prey. This is the first demonstration of the mechanism involved in the preservation of provisions in a hunting wasp. Some kind of preservation of prey as a component of parental care is probably widespread among hunting wasps and might have been a prerequisite for the evolution of mass provisioning.     

Foraging behavior of Cerulean Warblers during the breeding and non‐breeding seasons: evidence for the breeding currency hypothesis

Birds require additional resources for raising young, and the breeding currency hypothesis predicts that insectivorous species exploit large soft‐bodied prey during the breeding season, but shift to small, likely hard‐bodied, prey during the non‐breeding season. To test this hypothesis, we examined prey use by Cerulean Warblers (Setophaga cerulea), foliage‐gleaning Nearctic‐Neotropical migrants, during the breeding and non‐breeding seasons. We collected data on foraging behavior during the breeding season (including observations of prey items fed to young) in upland mixed‐oak forest in southeastern Ohio in 2009 and 2010 and, during the non‐breeding season, in shade coffee in the Cordillera de Merida, Venezuela, in 2008–2009. Cerulean Warblers captured 7% more large prey (visible prey extending beyond the bill) during the breeding than the non‐breeding season, but foraged at similar rates during both seasons. Large, soft‐bodied prey appeared to be especially important for feeding young. We found that adults delivered large prey on >50% of provisioning visits to nests and 69% of identifiable large prey fed to nestlings were greenish larvae (likely Lepidoptera or caterpillars) that camouflage against leaves where they would tend to be captured by foliage‐gleaning birds. Availability of specific taxa appeared to influence tree species foraging preferences. As reported by other researchers, we found that Cerulean Warblers selected trees in the genus Carya for foraging and our examination of caterpillar counts from the central Appalachian Mountains (Butler and Strazanac 2000 ) showed that caterpillars with greenish coloration, especially Baileya larvae, may be almost twice as abundant on Carya than Quercus. Our results provide evidence for the breeding currency hypothesis, and highlight the importance of caterpillars to a foliage‐gleaning migrant warbler of conservation concern.     

Brood ball size but not egg size correlates with maternal size in a dung beetle,Onthophagus atripennis

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Effects of habitat fragmentation on provisioning rates, diet and breeding success in two species of tit (great tit and blue tit)

The aim of this study was to examine the effects of forest fragmentation on the ability of parent birds to provide their young with an adequate food supply. To examine whether prey population densities of the great tit (Parus major L.) and the blue tit (P. caeruleus L.) vary between study areas in different forest size classes we compared provisioning rates and chick diet and related these parameters to breeding success. We filmed 217 nests over two breeding seasons and collected data on frass fall as a general estimate of caterpillar availability. Nests which were attended by none or one parent only during filming (n = 46) were excluded from the analyses. In both years and for both species feeding rates were highest in the smallest fragments and lowest in the large forest. There was also a suggestion that differences in feeding rates between areas vary between years. We found no consistent tendency for prey size to change with forest size, although both species brought slightly smaller prey items to the nest in the smallest forest fragments and feeding rates correlated negatively with prey size. Caterpillars were the main item fed to nestlings, in both species. We found no evidence to suggest that either frass fall or the proportion of caterpillars in the diet varied with forest size. There was also no correlation between mean frass fall and the total number of caterpillars brought to the nests, in either species. Breeding success, as measured by clutch size, brood size, fledging weight and fledging success, did not differ between the small fragments and the large forest, in either species. There was also no relationship between provisioning rate (as concerns volume of prey fed to nestlings and the quality of chick diet) and breeding success parameters. In conclusion, this study does not suggest suboptimal foraging or breeding conditions in small fragments compared to a nearby large forest, for either species. Received: 23 June 1997 / Accepted: 29 December 1997     

Activity patterns of females of the solitary bee Anthophora plumipes in relation to temperature, nectar supplies and body size

Abstract.

• 1 Patterns of activity at a large nesting aggregation and at foraging sites are described for females of the solitary bee Anthophora plumipes (Pallas). Changes in the quality and quantity of the resource collected by females provisioning cells are related to variation in female body mass and microclimate.
• 2 Activity at the nest site demonstrated relationships with aspects of the thermal environment experienced by A.plumipes. Measures of temperature showing significant relationships differed for females in different stages in the nesting cycle exhibiting characteristically different behaviour patterns.
• 3 Larger females emerged from nest tunnels earlier in the morning and provisioned cells at lower ambient temperatures than smaller individuals. Body size therefore predicts reproductive success at low ambient temperatures.
• 4 Pollen and nectar loads carried by females increased with ambient temperature. Because only one cell is completed per day and the size of offspring is determined by the quality and quantity of resource provided by the mother, the body size of individuals emerging in the following season will depend on interactions between climate and body size, in addition to any heritable component.
• 5 Variation in activity levels at foraging sites is attributed not only to thermal considerations, but also to variation in the quality of rewards available at different floral sources.

     

Parental food provisioning is related to nestling stress response in wild great tit nestlings: implications for the development of personality

Background

Variation in early nutrition is known to play an important role in shaping the behavioural development of individuals. Parental prey selection may have long-lasting behavioural influences. In birds foraging on arthropods, for instance, the specific prey types, e.g. spiders and caterpillars, matter as they have different levels of taurine which may have an effect on personality development. Here we investigated how naturally occurring variation in the amounts of spiders and caterpillars, provisioned to nestlings at day 4 and 8 after hatching, is related to the response to handling stress in a wild passerine, the great tit (Parus major). Broods were cross-fostered in a split-brood design allowing us to separate maternal and genetic effects from early rearing effects. Adult provisioning behaviour was monitored on day four and day eight after hatching using video recordings. Individual nestlings were subjected to a handling stress test at an age of 14 days, which is a validated proxy for exploratory behaviour as an adult.

Results

Variation in handling stress was mainly determined by the rearing environment. We show that, contrary to our predictions, not the amount of spider biomass, but the amount of caterpillar biomass delivered per nestling significantly affected individual performance in the stress test. Chicks provisioned with lower amounts of caterpillars exhibited a stronger stress response, reflecting faster exploratory behaviour later on in life, than individuals who received larger amounts of caterpillars.

Conclusions

These results suggest that natural variation in parental behaviour in wild birds modulates the developmental trajectories of their offspring's personality via food provisioning. Since parental provisioning behaviour might also reflect the local environmental conditions, provisioning behaviour may influence how nestlings respond to these local environmental conditions.

     

Effects of prey quality on social wasps when given a choice of prey

The effect of prey quality on foraging behavior and colony demographics of the social wasp Polistes fuscatus was examined by providing a choice between non‐toxic prey (Manduca sexta caterpillars) and sublethally toxic prey (Junonia coenia caterpillars), and then comparing the performance of these colonies to others given only the non‐toxic prey. In the choice, one of two types of Manduca were used: those fed an artificial diet or those fed plantain (Plantago lanceolata), which contains iridoid glycosides (IGs) that Junonia coenia store but which Manduca does not. Despite the negative correlation between the number of Junonia prey used and number of adult offspring produced, when a surplus of non‐toxic prey was available, the wasps did not completely avoid the toxic prey. However, they were more discriminating when the choice was between Manduca fed an artificial diet and Junonia fed plantain vs. when both prey species had eaten the plantain. Because the wasps had a choice of prey types and had a surplus of prey on about one‐third of the days, the wasps were able to take enough non‐toxic prey to avoid some of the negative consequences of IGs. For example, the total number of wasp offspring per nest was not affected, but mean weight of female offspring per colony was less for colonies given both prey types eating plantain, compared to that for colonies fed only non‐toxic prey, or those given a choice of non‐toxic prey vs. toxic prey. In addition, compared to the control (only non‐toxic prey), the proportion of males produced was less in the treatment that provided a clear contrast between non‐toxic and toxic prey. Why these wasps did not avoid the toxic prey is discussed.     

A double-edged sword: parental care increases risk of offspring infection by a maternally vectored parasite

Parental care can protect offspring from predators but can also create opportunities for parents to vector parasites to their offspring. We hypothesized that the risk of infection by maternally vectored parasites would increase with the frequency of mother–offspring contact. Ammophila spp. wasps (Hymenoptera: Sphecidae) build nests in which they rear a single offspring. Ammophila species exhibit varied offspring provisioning behaviours: some species enter the nest once to provision a single, large caterpillar, whereas others enter the nest repeatedly to provision with many smaller caterpillars. We hypothesized that each nest visit increases the risk of offspring parasitism by Paraxenos lugubris (Strepsiptera: Xenidae), whose infectious stages ride on the mother wasp (phoresy) to reach the vulnerable Ammophila offspring. We quantified parasitism risk by external examination of museum-curated Ammophila specimens—the anterior portion of P. lugubris protrudes between the adult host''s abdominal sclerites and reflects infection during the larval stage. As predicted, Ammophila species that receive larger numbers of provisions incur greater risks of parasitism, with nest provisioning behaviour explaining ca 90% of the interspecific variation in mean parasitism. These findings demonstrate that parental care can augment, rather than reduce, the risk of parasite transmission to offspring.     

Nesting biology of the potter wasp Rhynchium brunneum brunneum (Fabricius, 1793) (Hymenoptera: Vespidae: Eumeninae) in North Vietnam

Rhynchium brunneum brunneum (Fabricius, 1793) is a common species using trap nests in North Vietnam. The females chose the nest traps with diameters ranging from 5.5 to 17 mm. Nests consisted of a linear series of one to eleven brood cells separated by mud partitions. Brood cells were provisioned with caterpillars, and eggs were attached to the ceiling of the cells by a thin filament. The life history and sex ratio data of this species were recorded from April to early November. Its sex ratio is strongly male-biased, being multivoltine, likely with four generations per year, the last one overwintering in the prepupal stage. Nesting activity of the species was described with major activities such as nesting site selection, oviposition, prey collecting, and applying cell material. Only 53.3% of the provisioned cells were successful; the others were damaged by six parasitoid species or died during development for unknown reasons.     

The relationship of provision weight to adult weight and sex ratio in the solitary bee, Ceratina calcarata

ABSTRACT.

• 1 The female of the solitary bee Ceratina calcarata (Robertson) (Hymenoptera: Anthophoridae) excavates a tunnel in a pithy twig and then constructs and provisions a linear series of brood cells that make up her nest.
• 2 Adult females are, on the average, 1.3 times heavier than the males, a significant difference (P<0.001). There is no difference between the sexes in the amount of weight gained per unit of larval food.
• 3 Larger females occur because their provision masses are, on the average, 1.3 times heavier than male-producing provision masses, a significant difference (P<0.001).
• 4 Because mothers invest more time and energy in their daughters, Fisher's theory predicts that they should produce more sons. When available resources are fewer in a given year as reflected in lighter provision masses, more males are produced during the year.
• 5 The observed sex ratio did not differ significantly from the expected, calculated as mean female weight/mean male weight and was male-biased.
• 6 Unlike species which nest in pre-formed tunnels, the sex of any brood cell except the innermost is random with respect to that cell's position in the nest and the tunnel's depth and diameter. The innermost position contained offspring with a female biased sex ratio (P<0.005).

     

The evolution of progressive provisioning

Most nonsocial wasps and bees are mass provisioners (MP), sealingeach egg into its own cell containing all of the food requiredto reach maturity. Other species instead provision progressively,feeding their offspring only gradually as they develop and usuallyprovisioning more than one offspring simultaneously (SPP). Theevolution of progressive provisioning is interesting becauseit has obvious drawbacks. In particular, it could prolong theperiod of offspring dependency, and hence increase the chancethat a mother will die before her offspring reach independence.Prolonged dependency could in turn facilitate the evolutionof helping through insurance-based mechanisms. In this paper,I outline two ecologically extreme models of how reproductivesuccess is accrued during provisioning. In Model 1, immatureoffspring become independent as soon as they are fully provisioned.SPP is then disadvantageous because it prolongs the provisioningperiod compared with MP. If SPP does evolve, Model 1 predictsthat brood size, the number of offspring provisioned simultaneouslyin a batch, should be minimized. Model 2 differs from Model1 in that offspring become independent only at adulthood. SPPcan then be advantageous because investment is converted intoindependent offspring more quickly than under MP. Model 2 predictsan intermediate brood size, positively correlated with larvaldevelopment time and the abundance of provisions. Ammophilinedigger wasps and eusocial vespids may correspond to Models 1and 2, respectively, whereas ground-nesting wasps and bees withmulticellular nests may be intermediate.     

The Nesting Behavior of Dawson's Burrowing Bee, Amegilla dawsoni (Hymenoptera: Anthophorini), and the Production of Offspring of Different Sizes

Females of Dawson's burrowing bees have a well-defined brood cell cycle involving cell construction, waxing, provisioning, egg laying, and cell capping. In one study population, nesting bees built smaller brood cells for offspring of lower weight and larger ones for heavier offspring, demonstrating their ability to anticipate the desired size of an offspring at the outset of a brood cell cycle. Furthermore, individual females varied the number of provisioning trips made per brood cell cycle by a factor of two or more, apparently exercising control over the amount of brood provisions supplied to an offspring. The size distribution of emerging males at two widely separated locations in 1997 was nearly identical to that recorded in 1995. These findings suggest that the production of small males (minors) is the result of active female control rather than the product of food shortages that force females to undersupply some brood cells. Female foraging decisions resulted in a bimodal distribution of weights of mature dormant larvae at one site in 1997. However, the times required to complete brood cell cycles at this site were not distributed bimodally. This result stemmed in part from daily variation among females in the duration of their provisioning trips as well as from seasonal variation in provisioning trip times. When provisioning trips lasted longer, females tended to make fewer trips per brood cell cycle, and so were presumably more likely to produce minor sons. As a result, the weight of an offspring was not tightly linked to the time investment required to produce it, making it difficult to compare the relative costs of minors and majors in terms of maternal time investments.     

The influence of diet on growth and secretion behaviour of myrmecophilous Polyommatus icarus caterpillars (Lepidoptera: Lycaenidae)

Abstract.

• 1 Caterpillars of the facultatively myrmecophilous butterfly Polyommatus icarus were reared on inflorescences, or foliage, of four natural hostplant species and on an artificial diet to study dietary effects on larval growth and secretory capacity.
• 2 Caterpillars achieved highest weights and relative growth rates when fed flowers of Medicago sativa, Lotus corniculatus or Melilotus officinalis. Larvae reared on Coroniüa varia (flowers and leaves), foliage of M.sativa and on the artificial diet pupated at lower weights and achieved lower growth rates.
• 3 In standardized experiments with the ant species Lasius flavus, secretion rates from the dorsal nectar organ (DNO) were 2 times higher among flower-fed caterpillars than among foliage-fed siblings or caterpillars on the artificial diet. Larvae reared on C.varia flowers were superior to all other food treatments with respect to secretion rates.
• 4 High water content of larval diet, as in flowers, appears to be important for lycaenid caterpillars to achieve high secretion rates, whereas the correlation between myrmecophily and nutrient availability, as evidenced by growth rates, was less pronounced.
• 5 Using experimental data on larval growth and secretion rates, the lifetime volume of secretions from the DNO is estimated to range from 2 to 5 μl in most food treatments. Only on C.varia flowers (5.5–8.7 μl) and on M.sativa leaves (0.9–1.1 μl) did the caterpillars deviate in their absolute investment in myrmecophily.
• 6 The estimated lifetime investment accounted for 1.6–5.5% of prepupal fresh weight in all food treatments except on C.varia flowers (7.8–12.3%).

     

Parental provisioning behaviour in a flock-living passerine, the Vinous-throated Parrotbill Paradoxornis webbianus

The amount of food delivered by parents to their chicks is affected by various life history traits as well as environmental and social factors, and this investment ultimately determines the current and future fitness of parents and their offspring. We studied parental provisioning behaviour in the Vinous-throated Parrotbill Paradoxornis webbianus, a species with an unusual social system that is characterised by flock-living, weak territoriality and variable nesting dispersion. Parental provisioning rate had a positive influence on chick mass gain, suggesting that provisioning rate is an effective measure of parental investment in this species. Males and females fed nestlings at approximately the same rate, and no other carers were observed at nests. Parents coordinated provisioning rates so that they mostly fed chicks synchronously. However, the extent to which parents coordinated provisioning was associated with their social environment, synchrony being positively related to local breeding density and negatively to nearest neighbour distance. The rate at which parents provisioned nestlings showed the same relationships with social measures, being greatest at higher density and when neighbours were closer. Visit rate was also related to chick age, but not to brood size, brood sex ratio, extra pair paternity, laying date, temperature, parents’ body characters, time of day or year. We conclude that a breeding pairs’ social environment plays an important role in determining parental investment, probably through its effects on the opportunities that parents have for foraging with conspecifics.     

Why make daughters larger? Maternal sex-allocation and sex-dependent selection for body size in a mass-provisioning wasp, Trypoxylon politum

Mass-provisioning wasps package maternal investment into broodcells, sealed structures that contain all the provisions necessaryfor an offspring's growth and development. Optimal sex-allocationtheory predicts that if maternal provisions determine the sizeof each offspring, and the amount of provisions available toeach offspring varies, females should allocate well-stockedbrood cells to the sex that benefits most from being large.I tested this hypothesis using observations of organ-pipe wasps,Trypoxylon politum, and dissections of their nests. A Mississippipopulation of T. politum was intensively studied from 1993 to1995. This population fit the assumptions of optimal sex-allocationmodels by Green and Brockmann and Grafen. Female weight at emergencewas 1.29 times that of males, and wing length was 1.15 timesthat of males. This discrepancy in size occurred because thevolume of parental provisions strongly influenced adult bodysize, and better-stocked brood cells were preferentially allocatedto daughters. Brood-cell volume correlated with both wing lengthand weight at emergence in both sexes, and the chance that agiven brood cell contained a female offspring increased withincreasing brood-cell volume. Fitness was positively relatedto body size for females, but I found no evidence of an advantageto large males. Although there was evidence of stabilizing selectionfor male wing length in one year, there was no evidence of anincreasing relationship between body size and fitness (directionalselection) for males in either 1993 or 1994. Female fecunditywas positively related to body size in both years, indicatingthat larger females have increased reproductive success. Therate at which females provisioned brood cells was also correlatedwith body size. Observed patterns of investment in brood cellsare quantitatively consistent with the predictions of optimalsex-allocation theory, but certain aspects of female provisioningbehavior suggest females are not following a single "optimal"strategy. Patterns of provisioning were variable among differentfemales at the study site during the same year. Large femalestended to produce larger offspring. Although Brockmann and Grafen'smodel predicts a single, population wide "switchpoint" fromthe production of male to female offspring, there was no evidencefor such a switchpoint     

Only the largest terrestrial carnivores increase their dietary breadth with increasing prey richness

1. Animals should adapt their foraging habits, changing their dietary breadth in response to variation in the richness and availability of food resources. Understanding how species modify their dietary breadth according to variation in resource richness would support predictions of their responses to environmental changes that alter prey communities.
2. We evaluated relationships between the dietary breadth of large terrestrial carnivores and the local richness of large prey (defined as the number of species). We tested alternative predictions suggested by ecological and evolutionary theories: with increasing prey richness, species would (1) show a more diverse diet, thus broadening their dietary breadth, or (2) narrow their dietary breadth, indicating specialisation on a smaller number of prey.
3. We collated data from 505 studies of the diets of 12 species of large terrestrial mammalian carnivores to model relationships between two indices of dietary breadth and local prey richness.
4. For the majority of species, we found no evidence for narrowing dietary breadth (i.e. increased specialisation) with increasing prey richness. Although the snow leopard and the dhole appeared to use a lower number of large prey species with increasing prey richness, larger sample sizes are needed to support this result.
5. With increasing prey richness, the five largest carnivores (puma Puma concolor, spotted hyaena Crocuta crocuta, jaguar Panthera onca, lion Panthera leo, and tiger Panthera tigris), plus the Eurasian lynx Lynx lynx and the grey wolf Canis lupus (which are usually top predators in the areas from which data were obtained), showed greater dietary breadth and/or used a greater number of large prey species (i.e. increased generalism).
6. We suggest that dominant large carnivores encounter little competition in expanding their dietary breadth with increasing prey richness; conversely, the dietary niche of subordinate large carnivores is limited by competition with larger, dominant predators. We suggest that, over evolutionary time, resource partitioning is more important in shaping the dietary niche of smaller, inferior competitors than the niche of dominant ones.

     

How many can you catch? Factors influencing the occurrence of multi-prey loading in provisioning Greater Crested Terns§

Seabirds use several methods to transport food to their chicks; most species carry food in their stomachs or crops, but some terns and auks carry prey in their bills. Terns usually only carry one prey item at a time, limiting the rate at which they can provision their chicks, and restricting their effective foraging range. However, some terns do occasionally carry multiple prey, which should offer a selective advantage, but there are very few studies investigating the factors influencing the occurrence of multi-prey loading. We investigated the occurrence of multi-prey loads in provisioning Greater Crested Terns (Swift Tern) Thalasseus bergii bergii breeding on Robben Island, South Africa. Of 24 173 loads photographed, 1.3% comprised multiple prey items. Up to 11 fish were carried at once, but most multi-prey loads contained two Anchovies Engraulis encrasicolus, the most common prey item for this population of terns. Mixed species prey were recorded for the first time in a tern. Multi-prey loads occurred more frequently during mid- and late-provisioning, presumably because large chicks can cope with multiple prey, and have higher energetic requirements than small chicks. Mean standard length of Anchovies in multi-prey prey loads was less than Anchovies in single loads, possibly suggesting terns compensate for smaller prey sizes by bringing multiple prey back to their chick. The orientation of multiple Anchovies in a tern’s bill tended to be the same, suggesting that they were captured from polarised fish schools. At least some multi-prey loads were caught in a single dive.     

Effects of predation risk and plant resistance on Manduca sexta caterpillar feeding behaviour and physiology

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