Influence of temporal fluctuations in seed abundance on the foraging behaviour of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

The simultaneous study of the temporal dynamics of foraging behaviour, diet and seed abundance is essential to assess the way in which resources affect the behaviour and ecology of harvester ants. Here, we evaluate how fluctuations in grass seed abundance during three consecutive growing seasons influenced the foraging behaviour and diet of the harvester ants Pogonomyrmex rastratus, P. mendozanus and P. inermis in the central Monte desert, Argentina. Seed abundance of the most consumed grasses varied greatly through ant activity season, and ants altered their foraging behaviour in response to those changes. Foragers spent more time travelling and searching for food, and their foraging trips took longer during the low seed availability season. Foraging distance was very similar among species and, contrary to our expectations, did not vary between seasons. Foraging success of P. rastratus and P. inermis increased during the high availability season. This matched the seasonal pattern of foraging activity, suggesting that colonies may detect seed abundance and regulate their foraging effort with the rate of forager success. Although grass seeds were the main item in the diet of the three species, P. mendozanus, and to a lesser extent P. rastratus, turned more generalist when grass seeds were scarce. In contrast, P. inermis showed a very narrow diet breadth, only harvesting grass seeds in both seasons. Our results indicate the relevance of seed availability on foraging behaviour of harvester ants, which should be taken into account when predicting and evaluating the effect of ants on seed resources as well as numerical responses of harvester ant populations to the temporal and spatial variations in grass seed abundance.     

Diving pattern and performance in relation to foraging ecology in the gentoo penguin, Pygoscelis papua

We present data on diving pattern and performance (dive depth, duration, frequency and organization during the foraging trip) in gentoo penguins Pygoscelis papua , obtained using time-depth recorders ( n = 9 birds, 99 foraging trips). These data are used to estimate various parameters of foraging activity, e.g. foraging range, prey capture rates, and are compared in relation to breeding chronology. Foraging trip duration was 6 h and 10 h, and trip frequency 1.0/day and 0.96/day, during the brooding and creche periods, respectively. Birds spent on average 52%of each foraging trip diving. Dive depth and duration were highly bimodal: shallow dives (< 21 m) averaged 4 m and 0.23 min, and deep dives (> 30 m) 80 m and 2.5 min, respectively. Birds spent on average 71%and 25%of total diving time in deep and shallow dives, respectively. For deep dives, dive duration exceeded the subsequent surface interval, but shallow dives were followed by surface intervals 2–3 times dive duration. We suggest that most shallow dives are searching/exploratory dives and most deep dives are feeding dives. Deep dives showed clear diel patterns averaging 40 m at dawn and dusk and 80–90 m at midday. Estimated foraging ranges were 2.3 km and 4.1 km during the brood and creche period, respectively. Foraging trip duration increased by 4 h between the brood and creche periods but total time spent in deep dives (i.e. time spent feeding) was the same (3 h). Of 99 foraging trips, 56%consisted of only one dive bout and 44%of 2–4 bouts delimited by extended surface intervals > 10 min. We suggest that this pattern of diving activity reflects variation in spatial distribution of prey rather than the effect of physiological constraints on diving ability.     

Food and foraging behaviour of the Snares fernbird

Abstract

The Snares fernbird (Bowdleria punctata caudata Buller, 1894) is an opportunistic insectivore, its prey ranging greatly in size and type. Birds forage over a wide variety of sites, including forest, tussock, boulder beaches, cliffs, penguin colonies, and floating kelp. Foraging methods vary with the prey sought, and at times birds adopt specific “search images” when hunting certain insects. Details of foods brought to nestlings are given. Four postures used by fernbirds when foraging actively are described.     

FORAGING BEHAVIOUR OF NONBREEDING IMPERIAL CORMORANTS AT THE PRINCE EDWARD ISLANDS

Cooper, J. 1985. Foraging behaviour of nonbreeding Imperial Cormorants at the Prince Edward Islands. Ostrich 56: 96–100.

The Imperial Cormorant Phalacrocorax atriceps is an inshore, primarily solitary forager in the nonbreeding season at the Prince Edward Islands. All girds foraged within 400m of the coast, most seaward of a thick Macrocystis kelp bed. Mean dive duration was 40,2s with a maximum of 88s. The ratio of dives to surface rests was 2,68. Birds foraging very close inshore in shallow (<2 m) water dived for shorter periods than those farther offshore in deeper water. The Imperial Cormorant at the Prince Edward Islands appears to be rimarily a bottom-feeder. Foraging bouts were of short duration and little time was spent flying luring foraging. Imperial Cormorants dive for longer periods than do nearly all other species of cormorants.     

Effects of ants on the foraging of birds in spruce trees

I experimentally excluded ants from randomly selected spruce trees Picea abies near colonies of the wood ant Formica aquilonia. Foraging activity of birds in these trees was then compared to the foraging activity of birds in neighboring spruce trees, where ants were allowed to continue foraging. Birds which foraged in the foliage showed the effects of competition with ants: they visited the trees without ants more frequently, and for longer periods. In addition, the insects and spiders that they utilized as food were more abundant in the foliage of trees without ants. Cone-foraging birds, however, which fed on seeds in cones at the tops of the trees, did not show a preference for trees without ants. The differences of tree usage between foliage-gleaning and coneforaging birds can be explained by alteration of the birds' food supply by wood ants: ants did not feed on seeds in cones, and so did not compete with cone-foraging birds. However, foraging wood ants did feed on arthropods living in the foliage, thus reducing the amount of food available to birds there.     

BIOLOGY OF THE BANK CORMORANT,PART 3: FORAGING BEHAVIOUR

Cooper, J. 1985. Biology of the Bank Cormorant, Part 3: Foraging behaviour. Ostrich 56: 86–95.

The Bank Cormorant Phalacrocorax neglectus, endemic to southern Africa, is primarily a solitary inshore forager. Bank Cormorants forage Primarily on the bottom among kelp beds but also may forage over shingle or coarse sand substrates or in midwater. Breeding birds forage up to 9 km from their colony. Little is known of foraging depth but birds may dive as deep as 28 m. Mean dive duration was 44,9 s and ratio of dives to surface rests was 2,18. In most cases prey is swallowed under water, presumably to avoid kleptoparasitism. Bank Cormorants foraged during daylight hours from before sunrise to after sunset. Birds did not forage in exceptionally rough seas. Mean female foraging bout duration (84,3 min) was significantly longer than that of males (68,4 min) in breeding individuals. Breeding males undertook significantly more foraging bouts (3,47 boutdday) than did females (3,02 bouts/day). No significant differences were found between the sexes when total time spent foraging/day by breeding birds was compared. It is not clear why males foraged more often, but for shorter periods, than did females, but the differences may be related to sexual dimorphism, males being larger than females.     

THIRD REPORT OF THE S.A.O.S. LIST COMMITTEE

Tye, A. 1988. Foraging behaviour and selection of prey and perches by the Buffstreaked Chat Oenanthe bifasciata. Ostrich 59: 105–115.

Non-breeding Buffstreaked Chats Oenanthe bifasciata were studied in the Natal Drakensberg. Birds spent over 70% of their time foraging and 20% resting; both sexes sang, males c. 16% of the time. Individuals occupied overlapping home ranges; intra- and inter-specific aggressive interactions were recorded. Most foraging was by ground and aerial sallying from boulders, and all foraging methods were essentially sit-and-wait techniques. Buffstreaked Chats' most preferred perches were rocks 1,5-3 m high. Perches 1,5-3 m high were more likely to yield an aerial sally, while perches < 1,5 m were more likely to yield a ground sally or to be abandoned without a foraging attempt. Giving-up times were longer on perches 1,5-3 m high, but pre-capture waiting times were similar for perches of all heights. Giving-up times were longer than pre-capture times on perches 1,5-3 m high, but of similar duration to pre-capture times on lower perches. The major prey was grasshoppers, though ants, beetles, spiders and other insects were also eaten. When termites were swarming, birds switched to hunting them almost exclusively, thereby increasing their biomass intake rate. When termites were not available, at least 31% of the diet comprised prey 2 6 mm long. Aspects of the Buffstreaked Chat's biology are compared with other members of the genus Oenanthe.     

Foraging strategies of yakushima macaques (Macaca fuscata yakui )

I investigated the activity budget and diet of Yakushima macaques (Macaca fuscata yakui,)in warm temperate broad- leaved forest of Yakushima, Japan. Both time spent feeding and time spent moving varied considerably between half- months. However, total time spent in active behaviors— feeding time plus moving time— was stable. The composition of the diet also showed considerable variation between half- months. The macaques fed mainly on fruits, seeds,mature leaves, fallen seeds, flowers, and young leaves, each of which accounted for more than 30% of feeding time in at least 1 half- month. They also ate insects and fungi, but each of them comprised ≤ 25 and ≤ 8% of feeding time in any half- month, respectively. Time spent feeding on mature leaves, young leaves, flowers, or fallen seeds is positively correlated with total time feeding and is negatively correlated with time moving. In contrast, time feeding on fruits, seeds, insects or fungi is negatively correlated with time feeding and is positively correlated with time moving. Foraging on foods that have a low energy content, a high density, and a relatively even distribution— mature leaves— or that need much manipulation to be processed— flowers and fallen seeds— increased feeding time, while foraging on foods for which monkeys must search intensively in the forest— fruits, seeds, insects, and fungi— led to increased moving time. I examined foraging strategies of Yakushima macaques in terms of moving costs and the quality of food items. Regarding time feeding on fruits, which have more energy and may need less manipulation than other foods, as a benefit, and moving time as a cost, they seemed to employ a strategy that balanced the costs and benefits of foraging.     

Influence of temporal fluctuations in seed abundance on the diet of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

Harvester ants usually go through temporal fluctuations in environmental seed abundance and composition which could influence their behaviour and ecology. The aim of this study was to evaluate how these fluctuations influence the diet of Pogonomyrmex rastratus, P. pronotalis and P. inermis (Hymenoptera, Formicidae) in the central Monte desert during three consecutive growing seasons. Although seeds were the main item in the diet, these ants turned more generalist when seed abundance of the most consumed species (grasses Aristida spp., Trichloris crinita, Pappophorum spp., Digitaria californica and Stipa ichu) was low. Accordingly, diversity of items in the diet decreased with seed abundance in a logarithmical fashion, showing higher foraging efficiency for seeds at higher seed abundance. Seed diversity, however, was not related to seed abundance as ants always included several species in their diet, with alternating prevalence. The proportion of the most consumed species increased logarithmically in the diet of P. rastratus and P. pronotalis along with their abundance in the environment probably as a consequence of diet switching (from forb and shrub seeds to grass seeds) and by an increase in foraging efficiency at higher seed densities. In contrast, foraging activity of P. inermis was very low at low seed abundance and its diet included only the five grasses. Among the most consumed species, proportion in the diet was not associated with relative abundance in the environment. Aristida spp., Pappophorum spp. and D. californica were overall highly selected. However, the flexibility in the diet of P. pronotalis and P. rastratus and the low foraging activity of P. inermis during periods of low resource abundance could attenuate potential top‐down effects in the central Monte desert. This study shows that bottom‐up effects are important in ant‐seed interactions and should be considered when predicting and evaluating ants' effects on seed resources.     

The dynamics of seed harvesting in early successional communities by a tropical ant,Solenopsis geminata

Summary The neotropical ant, Solenopsis geminata, in the moist lowlands of southeastern Mexico was most abundant in agricultural fields and early second growth habitats. It was not found within forest habitats.In addition to its foraging for insects and general scavenging, this ant also harvests seeds. Under field experimental conditions, a wide variety of small seeds, especially grasses, were taken. Nest mound size and number were greatest on plots experimentally seeded to high grass density and low on plots consisting of grass-dicot mixtures, pure dicot stands, or a vegetative grass strain incapable of seed production. Paspalum conjugatum, an important grass weed, was the most common seed encountered in seed storage chambers in the mounds. Under experimental field conditions, Solenopsis geminata reduced seed densities of P. conjugatum and the malvaceous weed, Malachra sp. by 97 percent or more. Seed densities of the composite, Bidens pilosa were unaffected.     

Barlow's Lark: a new species in the Karoo Lark Certhilauda albescens complex of southwest Africa

The Karoo Lark Certhilauda albescens complex, endemic to southwest Africa, is characterized by regional phenotypic variation. Recent consensus has been to recognize two species, Dune Lark Certhilauda erythrochlamys and Karoo Lark Certhilauda albescens, but intermediate forms around the mouth of the Orange River have resulted in some authors treating it as a single polytypic species complex. We reexamined the status of taxa in this group by sequencing a segment of the mitochondrial DNA cytochrome b gene. Most samples were from the area around the mouth of the Orange River, where there is considerable local phenotypic variation. Our results indicate that the complex comprises three species, Karoo Lark, Dune Lark and Barlow's Lark Certhilauda barlowi, separated by 1.9-5.5% sequence divergence. There were no sequence differences among described subspecies, but there was limited variation among Dune Lark individuals (sequence divergence values 0.2-0.4%). The Red Lark Certhilauda burra is closely related to the Karoo Lark complex; indeed, it may be that Karoo Lark is the ancestral form. There was morphological (biometrics and plumage) and behavioural (male display song structure) support for the recognition of Barlow's Lark as a separate species. Species ranges within the complex are allopatric or narrowly parapatric, and they occur in different habitats and climatic conditions. Discriminant function analysis correctly identified 99% of skins assigned to taxa based on range, but a few individuals collected in the contact zone between Karoo and Barlow's Larks exhibited intermediate phenotypes, and further investigations are warranted to search for evidence of hybridization. The newly recognized Barlow's Lark has a maximum range of 18,000 km². It appears to have disappeared from heavily grazed farms around Aus, southern Namibia, and occurs almost exclusively in diamond mining areas, where domestic livestock are excluded. Changes to land use practices which reduce vegetation cover could seriously impact this species.     

Foraging strategies of yakushima macaques(Macaca fuscata yakui)

I investigated the activity budget and diet of Yakushima macaques (Macaca fuscata yakui,)in warm temperate broad- leaved forest of Yakushima, Japan. Both time spent feeding and time spent moving varied considerably between half- months. However, total time spent in active behaviors— feeding time plus moving time— was stable. The composition of the diet also showed considerable variation between half- months. The macaques fed mainly on fruits, seeds,mature leaves, fallen seeds, flowers, and young leaves, each of which accounted for more than 30% of feeding time in at least 1 half- month. They also ate insects and fungi, but each of them comprised ≤ 25 and ≤ 8% of feeding time in any half- month, respectively. Time spent feeding on mature leaves, young leaves, flowers, or fallen seeds is positively correlated with total time feeding and is negatively correlated with time moving. In contrast, time feeding on fruits, seeds, insects or fungi is negatively correlated with time feeding and is positively correlated with time moving. Foraging on foods that have a low energy content, a high density, and a relatively even distribution— mature leaves— or that need much manipulation to be processed— flowers and fallen seeds— increased feeding time, while foraging on foods for which monkeys must search intensively in the forest— fruits, seeds, insects, and fungi— led to increased moving time. I examined foraging strategies of Yakushima macaques in terms of moving costs and the quality of food items. Regarding time feeding on fruits, which have more energy and may need less manipulation than other foods, as a benefit, and moving time as a cost, they seemed to employ a strategy that balanced the costs and benefits of foraging.     

Linking traits of foraging animals to spatial patterns of plants: social and solitary ants generate opposing patterns of surviving seeds

Foraging traits of seed predators are expected to impact the spatial structure of plant populations, community dynamics and diversity. Yet, many of the key mechanisms governing distance- or density-dependent seed predation are poorly understood. We designed an extensive set of field experiments to test how seed predation by two harvester ant species interact with seed dispersal in shaping the spatial patterns of surviving seeds. We show that the Janzen–Connell establishment pattern can be generated by central-place foragers even if their focal point is located away from the seed source. Furthermore, we found that differences in the social behaviour of seed predators influence their sensitivity to seed density gradients and yield opposing spatial patterns of surviving seeds. Our results support the predictions of a recent theoretical framework that unifies apparently opposing plant establishment patterns, and suggest that differences in foraging traits among seed predators can drive divergent pathways of plant community dynamics.     

Taxonomic status of the Forest Buzzard Buteo oreophilus trizonatus

The foraging efficiencies of four sympatric southern African seed-eating birds, namely Bronze Mannikin Spermestes cucullatus, Cape Sparrow Passer melanurus, Southern Red Bishop Euplectes orix and Thick-billed Weaver Amblyospiza albifrons, and a domesticated species, the Bengalese Finch Lonchura domestica, were measured and compared using giving-up densities (the amount of food remaining following patch exploitation) in experimental food patches. Foraging efficiency was quantified using giving-up densities by offering individual birds equal foraging opportunities. A low giving-up density displays the ability of a forager to profitably harvest food at low resource densities and to gainfully exploit the foraging opportunities overlooked by a less efficient forager. Ten individuals of each of the five species were allowed to forage on six different seed types. Thick-billed Weavers had significantly lower giving-up densities for all seed types except the smallest, namely red manna. Bronze Mannikins showed the converse trend, foraging most efficiently on the smallest seeds. The results of the present study revealed that Thick-billed Weavers were the most efficient foragers (i.e. had the lowest giving-up densities on seeds in feeding trays).     

原始老龄林内兴安落叶松种子命运的试验研究

兴安落叶松土壤种子库的支出主要有３个方面：种子萌发、动物取食和生活力丧失。兴安落叶松种子在６月份迅速萌发,占全年总萌发量的９０％。７月中下旬,土壤已经不存在有生活力的种子。在生长季初期,鼠类对种子取食率仅１％,到生长季中后期接近２０％。然而,此时幼苗发生基本结束,被食种子大部分为生活力很弱或丧失生活力者。红背Ｐｉｎｇ是主要的食种子者。落叶松在时间上逃避了鼠类取食种子。一般,鼠类仅就地取食１０％的落     

Foraging ecology of the South Australian glossy black‐cockatoo (Calyptorhynchus lathami halmaturinus)

The endangered South Australian glossy black‐cockatoo (Calyptorhynchus lathami halmaturinus Mathews 1912) feeds almost exclusively on the seeds of the drooping sheoak (Allocasuarina verticillata), and shows marked preferences for individual trees. This field study investigated foraging ecology and tree selection through observations of foraging birds and measurements of trees and seed cones. The cockatoos spent the vast majority of their foraging time (94%) handling seed cones, and handling behaviour was highly stereotyped. Handling time per cone was correlated primarily with cone size, while seed intake rate was correlated primarily with seed mass per cone. The cockatoos fed mostly in trees with signs of previous feeding. They tended initially to sample trees with large seeds, and to stay for long feeding bouts in trees with high ratios of seed‐to‐cone mass. As a result of these biases, feeding was concentrated in trees with high seed mass per cone. Preferred trees were also larger, with higher ratios of seed‐to‐cone mass and larger seeds containing more lipid and protein. By feeding from selected trees the cockatoos increased both their seed intake rate and the nutritional quality of the seeds ingested, thereby increasing their energy intake rate by an estimated 28%. They did not discriminate against trees that had re‐grown from basal shoots after fires. Insect larvae were present in some seed cones but the cockatoos did not appear to actively seek them. Males foraged 19% more efficiently than females, resulting in greater daily food intake. The characteristics of individual A. verticillata trees that determined the cockatoos’ feeding rates were also correlated with their distribution on a regional scale. This suggests that the distribution of this endangered cockatoo depends not only on the presence of food trees, but also on their regionally varying feeding profitability.     

Foraging behavior of the midday gerbil (Meriones meridianus): combined effects of distance and microhabitat

We used the giving-up density (GUD) method and direct observation to study the combined effects of travel distance and microhabitat on foraging behavior of the midday gerbil (Meriones meridianus), which often acts as a central place forager. We provided animals with artificial seed trays in which dry and unhusked pumpkin seeds were mixed with fine sand. Gerbils practiced an eat-and-carry strategy in patches of bush microhabitat that were far from central places (BF patches), and tended to carry all seeds back in the other three treatments. Resource protection, predation risk avoidance and the balance between future and present value of food items may contribute to the eat-and-carry strategy. When distance was held constant, GUDs in open patches were higher than in bush patches, which was consistent with most studies. When microhabitat was held constant, GUDs in nearer patches were normally lower than in farther patches. In most cases, gerbils preferred to carry more seeds back rather than consume them immediately. We concluded that this tendency was due to the gerbils balancing the factors of future value and present value, and individual fitness and inclusive fitness.     

Competition between birds and mammals: A comparison of giving-up densities between crested larks and gerbils

We combined the concept of mechanisms of co-existence with the approach of giving-up densities to study inter-taxon competition between seed-eating birds and mammals. We measured feeding behaviour in food patches to define and study the guild of seed-eating vertebrates occupying sandy habitats at Bir Asluj, Negev Desert, Israel. Despite a large number of putatively granivorous rodents and birds at the site, two gerbil species (Allenbys gerbil, Gerbillus allenbyi, and the greater Egyptian gerbil, G. pyramidum) dominated nocturnal foraging, and a single bird species (crested lark, Galerida cristata) contributed all of the daytime foraging. We used giving-up densities to quantify foraging behaviour and foraging efficiencies. A low giving-up density demonstrates the ability of a forager to profitably harvest food at low abundances and to profitably utilize the foraging opportunities left behind by the less efficient forager. Gerbils had lower giving-up densities in the bush than open microhabitat, and lower giving-up densities in the semi-stabilized than stabilized sand habitats. Crested larks showed the opposite: lower giving-up densities in the open than bush, and on the stabilized than semi-stabilized sand habitats. Despite these patterns, gerbils had substantially lower giving-up densities than crested larks in both microhabitats, all sand habitats, and during each month. Several mechanisms may permit the crested lark to co-exist with the gerbils. Larks may be cream skimmers on the high spatial and temporal variability in seed abundances. Larks may rely on insects, fruit or smaller seeds. Or, larks may rely on adjacent rocky habitats.     

SHORT NOTES

Hockey, P.A.R., Plagényi, É.E., Turpie, J.K. &; Phillips, T.E. 1996. Foraging behaviour of Crab Plovers Dromas ardeola at Mida Creek, Kenya. Ostrich 67:33-44.

The foraging behaviour of Crab Plovers is directly analogous to the ‘walk-stop-search-walk’ hunting behaviour of true plovers, and changes slightly depending whether the birds are foraging on sand or in water: they are nonterritorial when foraging. Crabs dominate the diet, but other invertebrates and fish are also eaten. Foraging efficiency increases with age and adults and subadults are able to satisfy their daily energy requirements in a single tidal cycle. The population of Crab Plovers at Mida Creek was much larger in 1994 than in 1992, but in 1994 adults achieved much higher intake rates than in 1992, suggesting considerable year-to-year variation in the carrying capacity of Mida Creek for Crab Plovers. The world population of 43–50 000 birds breeds at very few colonies and the species is thus a potential conservation concern. Because of the relative accessibility of large concentrations of Crab Plovers away from the breeding grounds, we suggest that a programme to monitor numbers and population demography should be targeted at nonbreeding aggregations.     

Individual foraging components of harvester ants: movement patterns and seed patch fidelity

Summary We investigated individual foraging components of the western harvester ant,Pogonomyrmex occidentalis, in the native seed background of a shrub-steppe environment. Our study identified factors affecting foraging movements and seed selection by individual ants. Some assumptions and predictions of central-place foraging theory and a correlated random walk were evaluated for individual foragers. Results showed that ant size was only weakly correlated with the seed sizes harvested; seed size was a more important constraint than a predictor of seed selection. Individual ants spent more time in localized search behavior than traveling between search areas and nests.P. occidentalis foragers encountered seeds randomly with respect to time, and handled a mean of 1.7 seeds/trip. A correlation of increased search effort with greater travel distances was consistent with central-place foraging theory but, contrary to it, search and travel effort were not associated with energetic reward.Individual ants exhibited fidelity in both search site and native seed species. Spatial analyses of foraging movements showed a highly oriented travel path while running, and an area-restricted path while searching. Searching ants moved in a manner consistent with a correlated random walk. The deterministic component of patch fidelity and the stochastic component of search may override energetic foraging decisions in individualP. occidentalis ants.