Prey Handling Time Research Articles

Feeding economy of larvae of a flower fly,Metasyrphus corollae [Dip.: Syrphidae]: Partial consumption of prey

Metasyrphus corollae (F.) larvae ingested aphid contents at a decreasing rate over time because the contents of the aphid became increasingly difficult to obtain as the body of the prey was emptied. Starved larvae usually handled prey longer than wellfed larvae. Younger starved larvae fed longer than older larvae. Larvae starved for 24 h ate the most of a prey. Larvae held prey, on average, until 71% of dry mass was extracted after which the prey carcass was discarded. Prey handling time and amount of each prey consumed were determined by size and hunger of larvae and degree of depletion of prey contents.

Is Predaceous Stonefly Behavior Affected by Competition?

Behavioral experiments were carried out in flow-through observation boxes in New York and Colorado streams to determine whether interactions between pairs of predaceous stoneflies were characterized by exploitative or interference competition and to determine the effect of prey density on such interactions. The presence of a competitor generally reduced the number of attacks and the time that predaceous stoneflies spent eating mayflies (Baetidae). Coexisting perlids (Acroneuria carolinensis and Agnetina capitata) in the New York stream and perlodids (Megarcys signata and Kogotus modestus) in the Colorado stream had mutual negative effects on each other's foraging behavior despite significant size differences between species (first larger than second). A large omnivorous stonefly (Pteronarcella badia, Pteronarcydae) also suppressed the feeding behavior of Megarcys, but a reciprocal effect was not observed. Most competitive encounters resulted in submissive or evasive behavior by one or both stoneflies ultimately leading to avoidance of further contact. Some stoneflies, however, were occasionally aggressive, either toward conspecifics (Kogotus) or toward a smaller species of predator (Megarcys toward Kogotus). This behavior is consistent with the hypothesis that interference is a mechanism of competition among these stoneflies. The frequency of aggressive interactions increased for all stoneflies when prey density increased from 0 to 15 individuals per box but declined at 30 prey individuals per box. This observation suggests that the level of aggression is variable with availability of a food resource. As prey density increased, behavior associated with predator-prey interactions (attacks, feeding) increased for some stoneflies, and other activities (dispersal, cleaning, stationary behavior) decreased, generally increasing the pred- ator's probability of finding and consuming prey. Large species of stoneflies had shorter prey handling times than small species, and all stoneflies had very low rates of capture (successful captures 10-25% of total attacks). We postulate that direct interference competition from other stoneflies and predator- mediated dispersal of prey (unstable prey patches) reduce the benefit of aggregating in regions of high prey density.

Predation and Resource Partitioning in Two Sunfishes (Centrarchidae)

This study examines the diet and habitat use of two congeneric sunfishes in light of the effects of size—specific predation risk and foraging efficiency. Large bluegills (Lepomis macrochirus) and pumpkinseeds (L. gibbosus) (> 75 mm SL) exhibited distinct diet and habitat separation in three small Michigan lakes. Bluegills foraged primarily on open—water zooplankton (Daphnia), while pumpkinseeds specialized on vegetation—dwelling gastropods. These differences in resource use by large fish were directly related to differences in their functional morphology and foraging ability. In laboratory feeding experiments, pumpkinseeds had significantly lower prey handling times of gastropods than did bluegills. The bluegill, on the other hand, was the more efficient of the two species when feeding on zooplankton (Daphnia). In contrast to the large fish, the diets and habitat use of small bluegills and pumpkinseeds (@<75 mm SL) were quite similar. Small fish of both species foraged predominantly in the vegetation, and 76—91% of their average seasonal diet was vegetation—dwelling prey (nongastropods). This increase in shared resources among small fish was due to two factors: (1) piscivorous fish restrict small size—classes to the vegetation where they are less vulnerable, and (2) small pumpkinseeds are unable to feed effectively on snails, the adult resource in the vegetation. Laboratory comparisons of the foraging rate of small bluegills and pumpkinseeds on vegetation—dwelling prey, and field measures of the growth rate of each species while occupying the vegetation, indicate that the two species are nearly equal competitors in the juvenile habitat. The two species, however, were not in equal abundance across the study lakes; the ratio of bluegills to pumpkinseeds ranged from 25:1 to 1:1. The pattern in species abundance was directly related to the availability of "adult" resources (snails and zooplankton) in each of the lakes, suggesting that the volume of the competitive refuge experienced by each species at larger sizes is the predominant factor controlling their relative numbers.

The Functional Response of Toxorhynchites Rutilus Rutilus (Diptera: Culicidae), a Predator on Container-Breeding Mosquitoes1

This study approaches mosquito predation by Toxorhynchites r. rutilus in terms of the functional response of the predator. Toxorhynchites r. rutilus displays a Type II functional response, similar to that of most insect predators. Estimates of attack rates within and across its larval instars were not significantly different. The estimates for prey handling time showed no trend within the 4th instar, but decreased with each molt as the predator matured from 1st to 4th instar. At densities of 2 and 4 predators per container, attack rates decreased with increasing predator density, although they were not significantly different. Handling times significantly decreased as predator density increased. The study is summarized in the functional response surfaces for individual and total predator populations.

Hunting Behavior, Prey Selection, and Energetics of Snail Kites in Guyana: Consumer Choice by a Specialist

Abstract The hunting behavior, snail size selection, and time-activity patterns of non-breeding Snail Kites (Rostrhamus sociabilis sociabilis) were studied in Guyana rice fields. Kites spent 62% of the photoperiod perching, 19% foraging, 13% in maintenance activities, and 6% flying. As the day progressed, the percentage of daylight hours spent perching increased significantly, while foraging decreased significantly. Kites successfully captured and ingested Pomacea snails in 78% of the foraging bouts observed. The mode of hunting was evenly split between coursing (50.7%) and still-hunting (49.3%). Searching and returning times were related to time of day, as significantly more coursing hunts and still-hunts occurred in mornings and late afternoons, respectively. Prey handling time was the most time-consuming component of a foraging bout. Time spent searching for prey, returning, or handling prey was not related to snail size. The size distribution of captured snails differed significantly from that of available snails; kites selected more medium snails and fewer small snails and took large snails in equal frequency to that at which large snails were available. Kites captured the same-sized snails when coursing as when still-hunting. As rice grew, kite utilization of rice fields declined, and the frequency of still-hunting decreased while course-hunting attempts increased. The daily caloric intake of kites was estimated to be 104.2 kcal, the daily energy expenditure 85.7 kcal. Results are discussed in relation to consumer choices of specialists. The most important decision a foraging Snail Kite may make is what patch to search in and how long to search before abandoning patches.

EFFECTS OF STARVATION AND AGE ON FORAGING EFFICIENCY AND SPEED OF CONSUMPTION BY LARVAE OF A FLOWER FLY, METASYRPHUS COROLLAE (SYRPHIDAE)

AbstractStarved M. corollae Fab. larvae captured prey more quickly than unstarved larvae and older larvae, except those approaching pupation, sooner than younger larvae. Generally, older larvae also consumed prey more quickly but starvation increased prey handling time because starved larvae extracted 43% more, on average, from prey before discarding them. Significance of these findings for survival of M. corollae is discussed.

Feeding Ecology of Snowy Owls (<i>Nyctea scandiaca</i>) Wintering in Southern Alberta

Food habits, habitat selection, and hunting behavior of snowy owls ( Nyctea scandiaca ) wintering near Calgary, Alberta were investigated during the winters of 1976-77 and 1977-78. The owls preyed extensively upon rodents. Gray partridge ( Perdix perdix ) were an important prey only in one winter. Dietary differences between years seem to be related to differences in weather. Male snowy owls preyed almost exclusively upon mice, whereas females utilized a wider range of prey, including much larger species. The owls appeared to respond to variation in habitat quality by selecting those habitats with the highest availability of prey. Snowy owls were successful in 43% of 51 attempts to capture prey. The success rate of attempts to capture birds was lower than for small mammals. Juvenile females had lower success rates and longer prey-handling times than did adult females. Key words: snowy owl, Nyctea scandiaca , food habits, winter ecology, Alberta

Foraging Efficiency and Body Size: A Study of Optimal Diet and Habitat Use by Bluegills

A foraging model was developed to predict the optimal diet breadth and maximum energetic intake of a given—sized fish foraging in each of three aquatic habitats: the open water, vegetation, and bare sediments. Model parameters of prey encounter rates and prey handling times were quantified as functions of fish size, prey density, and prey size through a series of laboratory feeding experiments using the bluegill sunfish (Lepomis macrochirus). Results of these experiments show both searching ability and prey handling efficiency to increase with increasing fish size. Predictions of prey size selection and optimal habitat use based upon maximizing energetic gain were then examined in a small Michigan lake for three size classes of bluegills. Bluegills > 100 mm standard length were highly size selective in their feeding and their diets closely matched predictions of an optimal diet model. From two estimates of relative prey visibilities I show that these fish selected larger prey items than would be predicted if prey were consumed “as encountered.” Habitat use of large bluegills was also shown to maximize foraging return as fish switched from utilizing vegetation—living prey to utilizing open—water zooplankton as relative foraging profitabilities in the two habitats changed across the summer. Bluegills <100 mm standard length were restricted in their habitat use, remaining in or near the vegetation despite demonstrated increases in foraging return available in the open—water habitat. Size—related predation risk apparently accounts for differences in habitat use between bluegill size classes, and its consequences for intra— and interspecific competition between size classes are discussed.

The Role of Foraging Profitability and Experience in Habitat Use by the Bluegill Sunfish

This study integrates laboratory and field results to interpret habitat use and switching by individual bluegill sunfish (Lepomis macrochirus). Prey handling and search times for the bluegill were determined from laboratory feeding experiments at different prey sizes and densities in open water and sediment habitats. Relationships were then constructed to predict the expected return per unit time foraging in these habitats. Experience (learning) was found to increase foraging efficiency up to fourfold over the course of six to eight foraging bouts. A population of 225 bluegills was then introduced into a pond consisting predominantly of open water and sediment habitats. This population exhibited several habitat switches as resources declined during the 3—mo experiment; in addition, the population split over a 5—wk period, with individuals specializing on one habitat or the other. These specialists were considerably more successful than habitat generalists as measured by average amount of food in the stomachs. Return rates estimated from the laboratory experiments indicated that the two habitats were nearly equal in foraging profitability. The individual specialization indicated that learning and mutually interfering foraging mechanisms were involved in the species' use of the two habitats. The results suggest that learning and sampling are important aspects of both habitat use and the specialization of individuals within a population.

The Control of Handling Time and its Effects on the Foraging Strategy of a Heteropteran Predator, Notonecta

SUMMARY (1) The feeding behaviour of two species of the freshwater heteropteran Notonecta was examined with respect to the factors influencing prey handling time. (2) Overall mean handling time was found to increase with decreasing prey density, as predicted by both optimal feeding and gut-filling models. (3) A positive correlation was demonstrated between handling time and intercatch interval (the time from discarding one prey item to capturing another), supporting a gut-filling model. (4) A decay in the handling time per item through the catch sequence was found, irrespective of prey density, which adequately described the overall mean handling time for each prey density. (5) A similar decrease was demonstrated in the intercatch interval through the catch sequence, suggesting an increase in searching efficiency, which could be based on the

Seasonal Aspects of the Predatory Behavior of Loggerhead Shrikes

-Aspects of the foraging behavior of Loggerhead Shrikes were analyzed in the nonbreeding and breeding seasons in southern California. The birds obtained more food during the breeding season by attacking more often, not by taking larger prey. Attack rate during the breeding season was twice that in the nonbreeding period, with no apparent difference in capture efficiency. No distinct relationship between attack distance and capture efficiency was noted. Time between attacks decreased during breeding in response to greater food demands. Pursuit, encounter, and handling times did not significantly change between seasons. A positive significant correlation between prey handling time and the square of prey length was found. Handling time did not severely reduce the amount of time that could be devoted to hunting during any season. However, total movements averaged considerably higher during breeding than attack rate alone, adding to the energy expenditures of a hunting shrike and possibly placing constraints on the amount of hunting time available. An important part of the daily activity budget of an animal is that portion devoted to foraging. More food is needed during the breeding season, when the nutritional requirements of the nestlings must also be satisfied. Studies of the temporal patterns of foraging behavior thus lend insight into changing energy needs of a species. This study reports on the foraging behavior of the Loggerhead Shrike (Lanius ludovicianus). Impaling (caching) behavior has been discussed by Watson (1910) and Applegate (1977), and methods for carrying prey were noted by Esterly (1917) and Caldwell (1967). Slack (1975) hypothesized that shrikes select small prey that would be easier to catch, instead of larger prey that would provide more food once captured. Food items taken by shrikes were listed by Judd (1898), Stephens (1906), and Wayne (1921). An important paper by Craig (1978) described the various components of shrike attack behavior, mostly during the nonbreeding season. Attack behavior of shrikes might be expected to differ between nonbreeding and breeding seasons owing to the need to obtain additional food during breeding. I report here on differences in the components of a shrike's attack between breeding and nonbreeding seasons. STUDY AREA AND METHODS My 6-ha study area was in the southeast end of the Whittier Narrows Nature Center, South El Monte, Los Angeles County, California (elevation 67 m). The center was bordered by a channeled river on the south and by major roads and freeways on the remaining sides. Vegetation on the site was relatively homogeneous, consisting mainly of a low (< 1 m) growth of mustard (Brassica campestris) interspersed with grasses and herbs. Widely scattered elderberry (Sambucus mexicana) and walnut (Juglans californica) grew to 7 m. Transmission lines supported by three towers crossed the site. A chain-link fence and a dirt road ran parallel with the lines and b rdered the south edge of the site adjacent to the river; the river was about 50 m from the towers. From 24 December 1977 through 23 August 1978 I visited the study area for about 60 h on 31 days. During the pre-breeding season I collected data on seven adult shr kes occupying the area. Data were collected on one pair during the breeding and post-breeding seasons; this pair raised two broods of three young each during

The Feeding Biology of Ant-Lion Larvae: Prey Capture, Handling and Utilization

SUMMARY (1) The general feeding biology of Morter obscurus is described. (2) First instar larvae, because they use a different pit construction technique, have steeper-walled pits than later instars. Pit diameter and larval length are linearly related. (3) Capture success is determined mainly by the relative sizes of predator and prey. For a given relative size instar 1 larvae are more successful because of the steep-walled pits. Capture success drops to zero when ants can place some of their legs outside the pit. Third instar larvae were more successful than second instar larvae in pits of the same size. Capture success, particularly for large larvae, is 100% over much of the prey size range. (4) Successful attacks on ants with thick exoskeletons occurred almost exclusively via the gaster whereas mandible insertion for ants with thin exoskeletons frequently occurred elsewhere. (5) Differences in pit morphology and prey capture behaviour in Macroleon lynceus are documented and related to habitat differences. In Morter, pit morphology is crucial for prey capture, while strength is more important for the larger Macroleon. (6) Handling time was divided into time to capture (Ta), time to death (Td), and time to extract body contents (Te). T, was constant for small prey but increased rapidly for larger prey. Td was constant for all sizes of predator and prey. Te increased with prey size and decreased with increasing predator size and temperature. Te seems to depend not only on the amount of extractable food but also on the shape of the victim. (7) Hunger has no effect on prey handling time or food extraction efficiency. However hungry larvae are more likely to move their pits. Ant-lions can capture prey falling into the pit when already feeding and so increase their food supply. (8) Growth rates of larvae feeding on different sized prey were measured. Large larvae grew more slowly than small ones when fed on the same sized prey because of higher maintenance costs. For a given sized predator, growth per unit weight of prey received declined with increasing prey size because of increased feeding costs. Each size of ant-lion had a prey size for which the costs per unit return were a minimum, this size changing abruptly from very small prey for the first two instars to large prey for the final instar. (9) The feeding biology of the three instars is compared and contrasted. First instar larvae are adapted to achieve a high capture success rate on a small prey size range because feeding costs are high and escapes therefore expensive. For large larvae, maintenance costs are more important and selection has favoured a large size range of catchable prey. While the behaviour of ant-lion larvae is consistent with an energy maximizer strategy it is concluded that the approach is of limited value in this instance.

A Comparison of Predation Rates and Prey Handling times of Adult Notonecta and Buenoa (Hemiptera: Notonectidae)

With respect to quantifiable feeding patterns, Notonecta spp. differ from Buenoa spp. in higher predation rates, shorter prey handling times, and less food obtained from each prey. In all species, starvation results in both higher initial predation rates and shorter prey handling times.