Aerial Predators Research Articles

A comparative study of the costs of alternative mayfly oviposition behaviors

Oviposition behavior of insects has associated fitness costs related to the probability that females survive to oviposit. During summer 2003, we observed the oviposition behavior and compared the mortality rates of females of 17 mayfly species in one western Colorado watershed. We dissected adult females collected on terrestrial sticky traps, in drift nets submerged in streams, and in stomachs of brook trout to determine whether the mayflies had oviposited before capture, drowning, or consumption. Females oviposited by either splashing on the water surface releasing all their eggs (splashers), dropping their eggs from the air (bombers), dipping their abdomens multiple times releasing a few eggs at a time (dippers), landing on rocks and ovipositing on the undersides (landers), or floating downstream while releasing their eggs (floaters). Almost 100% of lander and 50% of dipper females had not oviposited when captured on sticky traps, increasing their vulnerability to preoviposition mortality by aerial predators compared to mayflies with other behaviors. In contrast, most females had laid their eggs before drowning or being eaten by a fish (50–90%). However, groups with oviposition behaviors most exposed to the water surface (floaters, then splashers, dippers, and landers) were more vulnerable to drowning before completing oviposition. In addition, splashers and floaters were most vulnerable to predation by brook trout before ovipositing. These data suggest that fitness costs associated with preoviposition mortality may be considerable depending on mayfly oviposition behavior. Furthermore, previously demonstrated benefits of low predation rates on eggs of lander species may be offset in part by costs to female survival.

Ruffed Grouse Brood Habitat Use in Mixed Softwood‐Hardwood Nordic‐Temperate Forests, Quebec, Canada

Abstract: Adequate cover is a critical component of ruffed grouse (Bonasa umbellus) habitat during the brood‐rearing period when chick mortality is high. We assessed habitat use by ruffed grouse during the brood‐rearing period by comparing characteristics of tree, shrub, and ground layers at ruffed grouse brood and random locations. We captured and radiomarked 29 females with broods in 2 forest settings of the Réserve faunique de Portneuf, Quebec, Canada. We described grouse habitat using ground surveys and forest maps, and we identified the used habitat characteristics using analysis of variance and logistic regression. Females with broods used mixed and regenerated clearcut stands that were 1.5–7 m tall and 11–20 years old. Compared with random locations, grouse locations had higher lateral obstruction (76% vs. 68%), higher small‐stem density (29,085 stems/ha vs. 19,340 stems/ha), and were closer to roads and trails. Percentage of coverage by ground vegetation was not higher at grouse locations as often reported in previous studies. Results from this study will help orient ruffed grouse habitat management on Quebec public land and elsewhere in nordic—temperate mixed hardwood—softwood forests to maintain suitable brood habitat after logging operations. Forest management should promote growth of young mixed stands with high horizontal and vertical cover provided by high small‐stem density, which offers protection against aerial and terrestrial predation. Edges such as roadsides are also important in brood habitat as they provide food and cover.

Avoiding predators at night: antipredator strategies in red‐tailed sportive lemurs (Lepilemur ruficaudatus)

Although about one-third of all primate species are nocturnal, their antipredator behavior has rarely been studied directly. Crypsis and a solitary lifestyle have traditionally been considered to be the main adaptive antipredator strategies of nocturnal primates. However, a number of recent studies have revealed that nocturnal primates are not as cryptic and solitary as previously suggested. Thus, the antipredator strategies available for diurnal primates that rely on early detection and warning of approaching predators may also be available to nocturnal species. In order to shed additional light on the antipredator strategies of nocturnal primates, I studied pair-living red-tailed sportive lemurs (Lepilemur ruficaudatus) in Western Madagascar. In an experimental field study I exposed adult sportive lemurs that lived in pairs and had offspring to playbacks of vocalizations of their main aerial and terrestrial predators, as well as to their own mobbing calls (barks) given in response to disturbances at their tree holes. I documented the subjects' immediate behavioral responses, including alarm calls, during the first minute following a playback. The sportive lemurs did not give alarm calls in response to predator call playbacks or to playbacks with barks. Other behavioral responses, such as gaze and escape directions, corresponded to the hunting strategies of the two classes of predators, suggesting that the corresponding vocalizations were correctly categorized. In response to barks, they scanned the ground and fled. Because barks do not indicate any specific threats, they are presumably general alarm calls. Thus, sportive lemurs do not rely on early warning of acoustically simulated predators; rather, they show adaptive escape strategies and use general alarm calls that are primarily directed toward the predator but may also serve to warn kin and pair-partners.

Tufted Puffins (Fratercula Cirrhata) Respond to Predation Danger During Colony Approach Flights

AbstractIn spite of their putative importance in the evolution of certain traits (e.g., nocturnality, coloniality, cliff nesting), the effects of aerial predators on behavior of adult seabirds at colonies have been poorly investigated. We hypothesized that Tufted Puffins (Fratercula cirrhata) respond to danger posed by aerial predators by modifying their behavior to mitigate danger. We observed Tufted Puffins making repeated colony fly-ins and departures and characterized (1) the timing of this behavior, (2) the activity rate (number of birds arriving or departing), and (3) the risk-level of activity, with respect to predation danger posed by Bald Eagles (Haliaeetus leucocephalus) and Peregrine Falcons (Falco peregrinus). As we predicted, we found that Tufted Puffins (1) dilute danger by synchronizing their fly-in and departure activities, (2) reduce fly-in and departure activity rates when predators are present, and (3) switch to lower-risk fly-in activities (e.g., staying over water where they have an escape route from an aerial attack) when predators are present.Réaction de Fratercula cirrhata au Danger de Prédation au cours des Vols d'Approche de la Colonie

TUFTED PUFFINS (FRATERCULA CIRRHATA) RESPOND TO PREDATION DANGER DURING COLONY APPROACH FLIGHTS

Abstract In spite of their putative importance in the evolution of certain traits (e.g., nocturnality, coloniality, cliff nesting), the effects of aerial predators on behavior of adult seabirds at colonies have been poorly investigated. We hypothesized that Tufted Puffins (Fratercula cirrhata) respond to danger posed by aerial predators by modifying their behavior to mitigate danger. We observed Tufted Puffins making repeated colony fly-ins and departures and characterized (1) the timing of this behavior, (2) the activity rate (number of birds arriving or departing), and (3) the risk-level of activity, with respect to predation danger posed by Bald Eagles (Haliaeetus leucocephalus) and Peregrine Falcons (Falco peregrinus). As we predicted, we found that Tufted Puffins (1) dilute danger by synchronizing their fly-in and departure activities, (2) reduce fly-in and departure activity rates when predators are present, and (3) switch to lower-risk fly-in activities (e.g., staying over water where they have an ...

VEGETATIVE AND FRUIT RESOURCES AS DETERMINANTS OF HABITAT USE BY MATURE-FOREST BIRDS DURING THE POSTBREEDING PERIOD

Recent studies have demonstrated that many birds of mature forests heavily use early-successional habitat during the postbreeding period. Two frequently invoked hypotheses to explain these shifts are that postbreeding birds select (1) dense cover to reduce risk of predation and (2) abundant fruit resources to facilitate foraging. Using mist nets between 15 June and 16 August in 2002 and 2003, we captured mature-forest birds during the postbreeding period in 12 regenerating hardwood clearcuts (three to seven years old) in southeast Ohio. Vegetation structure and fruit resources were measured at nine net locations within each clearcut. We applied an information-theoretic approach, where we used vegetative and fruit variables as predictors in seven a priori models to evaluate how habitat factors might explain capture rates. In two seasons, we captured 1,089 hatch-year (HY) and 445 after-hatch-year (AHY) postbreeding birds of 32 mature-forest species. In general, models reflecting habitat structure (density of low vegetation, canopy height) best explained variation in capture rates, which were negatively related to the density of low vegetation (<1.5 m) and positively related to canopy height. Extremely dense low vegetation may be disadvantageous if it inhibits movements and provides cryptic locations for ground predators. Instead, habitats with greater vertical structure (e.g., taller vegetation) and relatively less dense low vegetation below may provide better protection from aerial and ground predators. Overall, results suggest that vegetation structure may explain high use of early-successional forests by many birds during the postbreeding period, though fruit may be the most important factor for seasonal frugivores. Recursos Vegetativos y de Frutos como Determinantes del Uso de Hábitat por Aves de Bosque Maduro Durante el Período Posterior a la Reproducción

Age and seasonal effects on predator‐sensitive foraging in squirrel monkeys (Saimiri sciureus): a field experiment

A field experiment was conducted to examine the effect of perceived predation risk on the use of foraging areas by juvenile and adult primates under different conditions of local food abundance. Wild squirrel monkeys, Saimiri sciureus, were observed in an experiment conducted during the dry and the wet seasons at a site in Eastern Amazonia, Brazil. Animals were presented with feeding platforms that differed in food quantity and exposure to aerial predators through varying vegetative cover. In the dry season, juveniles and adults chose platforms based solely on food quantity. However, in the wet season, juveniles foraged preferentially on high-reward platforms only if cover level also was high (i.e., potentially offered greater concealment from predators). In contrast, adults showed the same pattern of platform use regardless of season. These results indicate that age and local resource availability based on seasonality affect whether primates forage in a predator-sensitive manner. Juveniles may be more sensitive to predation risk when foraging, and individuals may take fewer risks when resource abundance is high in their environment.

Microhabitat use by garden dormice during nocturnal activity

AbstractThe microhabitat used by the garden dormouse Eliomys quercinus during its nocturnal activity was examined. Twenty‐three variables describing habitat structure were measured at 100 trapping points. Logistic regression models were utilized to select the variables that discriminate between used and avoided trapping points and, in a series of pairwise contrasts, between trap sites used by different sexes, age classes and animals in different reproductive periods. Used sites were characterized by a higher (&gt;40%) rock cover, a thicker shrub layer and a younger understory with trees of smaller trunk diameter. These variables describe areas with rockfalls from the upper slope, where trees were younger and smaller, the canopy closure reduced and the shrub layer more developed than in other parts of the forest. Dense shrubby vegetation provided protection from aerial predators and, in conjunction with rocks and stones, might have made hunting by birds and mammals more difficult. Garden dormice may also have been attracted by rocky areas acting as a heat source during the night. The selection of rocky areas was more important in the first months of the active period, when animals emerged from hibernation and started the mating season. At the end of summer, the animals used areas richer in herbs, where insects and other food resources were probably more abundant.

Preliminary observations on habitat, support use and diet in two non-native primates in an urban Atlantic forest fragment: The capuchin monkey (Cebus sp.) and the common marmoset (Callithrix jacchus) in the Tijuca forest, Rio de Janeiro

Space is an important dimension of the ecological niche. Differentiation in the use of vertical strata of the forest is related to species body size, and explains in part species coexistence at a local scale. Large neotropical primates dwell in the canopy, moving quadrupedally on large branches, whereas smaller species leap between narrow branches in the understory. We tested this general pattern by observing focal individuals of the capuchin monkey (Cebus sp.) and the common marmoset (Callithrix jacchus), both non-native species, living in a forest fragment within the Rio de Janeiro city. Results were in accordance with the pattern for neotropical primates. Vertical use of the forest seems to be related with ecological interactions, especially for C. jacchus restricted to the lower strata due to aerial predation. Preliminary observations on diet corroborate the omnivory of Cebus and the gum feeding characteristic of C. jacchus. For Cebus sp. the exotic jack-fruit (Artocarpus heterophyllus) was the most important food item. Predation of both primates on vertebrates, especially by C. jacchus on passerines, could cause an uncommon impact on prey populations. In spite of anthropogenic impact, these non-native primates maintain the general pattern of habitat, support use and diet of the same or similar species in native neotropical communities.

Fat Affects Predator-Avoidance Behavior in Gray Catbirds (Dumetella Carolinensis) During Migratory Stopover

Abstract During migration, birds may store large quantities of fat to fuel long-distance flight. Because mass affects flight performance, fat migrants should behave with greater caution toward aerial predators than lean migrants. We tested a prediction of this hypothesis, namely, that fat birds will remain motionless longer than lean birds after a simulated encounter with a raptor. We captured Gray Catbirds (Dumetella carolinensis) during fall migration, classified their subcutaneous fat, exposed them to a model hawk, and then recorded the time until their first perch change. To determine whether the birds treated the simulated predator as a threat, we also tested them with a hexagon-shaped model and with no model. The birds remained motionless longer with the hawk model than either of the two other treatments. Fat birds remained motionless longer than lean birds when exposed to the hawk model, but we detected no difference with the other two treatments. These results provide evidence that fat affects the predator-avoidance behavior of Gray Catbirds during migratory stopover. That a difference between fat and lean groups was only apparent with the hawk model treatment suggests that the result is attributable to differences in the flight performance of the two groups rather than simply a difference in motivation to begin foraging. We suggest that fat should influence the behavior of a wide variety of migrant birds, particularly those species that typically carry greater fat reserves or that forage in more exposed situations than the Gray Catbirds we tested. La Grasa Afecta el Comportamiento de Evasión de Depredadores en Dumetella carolinensis durante las Paradas Migratorias

Antipredator Behavior of Brown Howlers Attacked by Black Hawk-eagle in Southern Brazil

In field studies between 2002 and 2004 in southern Brazil, we recorded antipredatory behaviors (N=9) of brown howlers (Alouatta guariba clamitans) under attack by the black hawk-eagle (Spizaetus tyrannus). We observed 2 types of behavioral responses: the descent to the understory followed by the dispersion of the group and immobility and silence. Brown howlers displayed behaviors specific to evading aerial predators, which are similar to the ones in other Neotropical primates.

Semantic Differences in Sifaka (Propithecus verreauxi)Alarm Calls: A Reflection of Genetic or Cultural Variants?

AbstractIn this study, we compared the usage of alarm calls and anti‐predator strategies between a captive and a wild lemur population. The wild lemur population was studied earlier in Western Madagascar (Fichtel &amp; Kappeler 2002). The captive population was studied in outdoor enclosures of the Duke University Primate Center. Alarm calls and anti‐predator behavior were elicited by conducting experiments with both vocal and visual dummies. We scored the subjects’ immediate behavioral responses, including alarm calls, from video recordings made during the experiments. In principle, both populations have a mixed alarm call system with functionally referential alarm calls for aerial predators and general alarm calls for terrestrial and aerial predators and for situations associated with high arousal, such as group encounters. Although wild and captive sifakas exhibit the same alarm call system and use the same alarm call types, we discovered striking differences in the usage and perception of some of the alarm calls. We argue that these differences indicate either an evolutionary drift in the meaning of these calls or reflect cultural variation. The latter possibility is consistent with our understanding of the ontogeny of call usage and comprehension.

Detection of a looming stimulus by the Jacky dragon: selective sensitivity to characteristics of an aerial predator

Rapidly looming objects are highly salient to most animal visual systems. The sensory processing of such stimuli is now well understood in birds and insects. We conducted the first analogous study in lizards, concentrating on the ecologically realistic challenge posed by an approaching aerial predator. In an initial experiment, video footage of a trained raptor flying towards the camera produced flight responses in Jacky dragons, Amphibolurus muricatus, but control sequences showing a retreating or stationary stimulus were ineffectual. Two additional experiments then explored the processing of motion and of morphological attributes separately. We presented a series of expanding disks, systematically manipulating area/time characteristics to test looming sensitivity in the absence of other cues. Lizards oriented significantly more frequently to a sequence matching the area change of the approaching predator than to any other. Comparisons show that this response was specific to an exponential increase following a period of slow change, a pattern remarkably similar to those described in other taxa. In the final experiment, we presented a range of stimulus shapes, all with identical area and movement. Lizards were most responsive to a realistic raptor silhouette. Controls allowed us to exclude the possibility that this result was attributable to looming rate, size or the axis of asymmetric expansion. We conclude that response to an approaching aerial predator depends upon a hierarchical series of cues, including area/time profile, edge length, shape and orientation. The integration of this information will be an important problem for future work.

Sleeping sites of black‐and‐white snub‐nosed monkeys (Rhinopithecus bieti) at Baima Snow Mountain, China

AbstractData on sleeping sites of a group of black‐and‐white snub‐nosed monkeys Rhinopithecus bieti (Colobinae, Primates) were collected between April–July and September–December 2001 to try to determine the factors affecting site selection at Nanren (99°04′E, 28°34′N, Baima Snow Mountain, China). Sleeping trees were tall emergents (27.5±3.2 m) with large diameter at breast height (57.9±16.9 cm) and broad crown diameters (6.3±1.4 m), and significantly larger than other trees. The use of large sleeping trees could provide effective shelters from attacks of terrestrial and aerial predators, heavy snow and rain. Sleeping sites were changed nightly and located at significantly lower altitudes in winter months than in other seasons, which might be a thermoregulatory adaptation or related to snow covering. Such sites tended to be at the middle of sun‐oriented slopes, possibly trading off predator avoidance and foraging efficiency.

Anti-Predator Behavioral Responses of Mosquito Pupae to Aerial Predation Risk

Aquatic insects have two potential sources of predation risk: aquatic predators and aerial predators. Our goal was to assess anti-predator responses of Culex pipiens to aerial predation. By simulating predator attacks, we assessed (a) the distance fled in relation to depth and group size, (b) the distribution of individuals at different depths, and (c) the duration of surfacing events to obtain air in scenarios with varying predation risk. Pupae located closer to the surface fled deeper into the water, and the number of conspecifics decreased the distance fled. When the risk of predation increased, more individuals were found deeper in the water column, and the interval between two consecutive surfacing events increased. Culex pipiens shows a trade-off between avoiding aerial predation and maintaining oxygen acquisition, which may be regulated by the need to conserve energy reserves.

Feeding Bout Lengths differ Between Terrestrial and Aquatic Feeding Coots Fulica atra

Abstract Similar to other bird species, Coots (Fulica atra) usually interrupt feeding to look up and to scan their environment for predators. Predation risk may differ among feeding methods. Coots may suffer from aerial predators both in the water and on land, and additionally from terrestrial predators when feeding on land. Samples were obtained from 10 different study sites where Coots fed both on water and on land (N = 139 feeding-bouts). Flock structure differed significantly between feeding methods, and nearest-neighbor distance was lower on land (water: 5.2 ± 0.3 Coot length, land: 2.8 ± 0.2 Coot length). Mean feeding-bout length--defined as the time of uninterrupted feeding--was significantly different (water: 12.2 ± 0.8 s, land: 9.4 ± 0.8 s). When using the study sites as samples, aquatic feeding-bouts were also significantly longer. In a general linear mixed model a significant influence of feeding method on feeding-bout length was found, again with a higher bout length in the water. Feeding-bout...

Functionally Referential Alarm Calls in Tamarins (Saguinus fuscicollis and Saguinus mystax) – Evidence from Playback Experiments

AbstractStudies on primate vocalisation have revealed different types of alarm call systems ranging from graded signals based on response urgency to functionally referential alarm calls that elicit predator‐specific reactions. In addition, alarm call systems that include both highly specific and other more unspecific calls have been reported. There has been consistent discussion on the possible factors leading to the evolution of different alarm call systems, among which is the need of qualitatively different escape strategies. We studied the alarm calls of free‐ranging saddleback and moustached tamarins (Saguinus fuscicollis and Saguinus mystax) in northeast Peru. Both species have predator‐specific alarm calls and show specific non‐vocal reactions. In response to aerial predators, they look upwards and quickly move downwards, while in response to terrestrial predators, they look downwards and sometimes approach the predator. We conducted playback experiments to test if the predator‐specific reactions could be elicited in the absence of the predator by the tamarins’ alarm calls alone. We found that in response to aerial alarm call playbacks the subjects looked significantly longer upwards, and in response to terrestrial alarm call playbacks they looked significantly longer downwards. Thus, the tamarins reacted as if external referents, i.e. information about the predator type or the appropriate reaction, were encoded in the acoustic features of the calls. In addition, we found no differences in the responses of S. fuscicollis and S. mystax whether the alarm call stimulus was produced by a conspecific or a heterospecific caller. Furthermore, it seems that S. fuscicollis terrestrial alarm calls were less specific than either S. mystax terrestrial predator alarms or either species’ aerial predator alarms, but because of the small sample size it is difficult to draw a final conclusion.

Landscape and anti‐predation determinants of nest‐site selection, nest distribution and productivity in a Mediterranean population of Long‐eared Owls Asio otus

Nest predation is an important determinant of owl breeding success. We studied Long‐eared Owl Asio otus productivity and attributes of nest‐sites at the microhabitat and landscape scales in a Mediterranean locality over an 8‐year period. We examined the effect on nest location and productivity of protective cover in concealing the nest from aerial and terrestrial predators. A dense cover of ivy and tree‐foliage at canopy level favoured nest location but not productivity. By contrast, high shrub cover beneath the nest was selected by Owls and was positively related to both the site reoccupancy rate and the overall number of young fledged. Pre‐fledging Owls use the ground, where they are exposed to terrestrial predators, which are much more abundant in the study area than are aerial predators. Our results therefore support the hypothesis that Owls adapt nest‐site choice to local sources of predation risk. As reported elsewhere, Long‐eared Owls in our study area showed restricted territoriality and nested in clusters. As active nest‐sites during the same breeding season were more than 1 km apart on average, and their productivity was never greater for clustered nests than for more isolated nests, nest aggregation could not be interpreted as a case of facultative colonial breeding, which has been reported for this species in other areas. Neither landscape variables indicative of the availability of foraging areas nor structural attributes that protect young from predators explained the remarkable scarcity of nests in half of the study area. Unmeasured factors such as human disturbance could explain the pattern of distribution of Long‐eared Owl nests.

FAT AFFECTS PREDATOR-AVOIDANCE BEHAVIOR IN GRAY CATBIRDS (DUMETELLA CAROLINENSIS) DURING MIGRATORY STOPOVER

Abstract During migration, birds may store large quantities of fat to fuel long-distance flight. Because mass affects flight performance, fat migrants should behave with greater caution toward aerial predators than lean migrants. We tested a prediction of this hypothesis, namely, that fat birds will remain motionless longer than lean birds after a simulated encounter with a raptor. We captured Gray Catbirds (Dumetella carolinensis) during fall migration, classified their subcutaneous fat, exposed them to a model hawk, and then recorded the time until their first perch change. To determine whether the birds treated the simulated predator as a threat, we also tested them with a hexagon-shaped model and with no model. The birds remained motionless longer with the hawk model than either of the two other treatments. Fat birds remained motionless longer than lean birds when exposed to the hawk model, but we detected no difference with the other two treatments. These results provide evidence that fat affects the...

How does the presence of predators influence the persistence of antipredator behavior?

We developed a virtual world to study the effect of predators on predator recognition. We trained a neural network to discriminate between the shapes of simulated aerial and terrestrial predators and non-predators. Then, the network's weighting values were fixed into the genomes of a set of autonomous agents. These animats were required to eat, avoid death due to starvation, and avoid predation, by fleeing from approaching predators. We systematically varied the predator's lethality, the mutation rate, the cost of fleeing a predator, and the presence or absence of aerial and terrestrial predators. We used ANOVA to analyse the average recognition ability (a measure of directional selection) and the standard deviation of recognition ability (a measure of relaxed selection) after 500 generations of selection. Mutation rate and the cost of flight had the greatest effect on both the average and standard deviation of recognition abilities. The loss of all predators relaxed selection on predator recognition abilities. The loss of specific predators had complex effects on recognition abilities. Persistence is largely influenced by escape costs.