Hunting mode and success of African Peregrines Falco peregrinus minor,does nesting habitat quality affect foraging efficiency?

Peregrine Falcon Falco peregrmus hunting behaviour was studied at nest-sites in three areas of South Africa over eight years. In Africa, resident Peregrines are mostly restricted to high cliffs, possibly because these structures provide optimal conditions for hunting. This hypothesis is examined in terms of the influence of nest-site quality, particularly cliff height, on foraging efficiency. Foraging mode varied considerably between sites, and males foraged more actively than females but there was little variation in the design of hunts between sexes, seasons or study areas. Individually, Peregrines spent 30–50% of the day on or near the nest cliff. On average, about 0.5 hunts were recorded per hour of observation. Foraging mode was not correlated with cliff height or elevation above the surrounding terrain, but Peregrine pairs occupying higher cliffs achieved greater hunting success rates. Most hunts were initiated from elevated perches on the nest cliff, and perch hunts were more successful than strikes made from the air. Success was highest in strikes at doves and small passerines, and over habitats with moderate cover. The height difference between Peregrine and prey at the start of a hunt positively and significantly affected hunting success. Overall, Peregrines were relatively sedentary and made extensive use of the nesting habitat as a foraging area. High nest cliffs contributed to foraging success by providing perch-hunting falcons with an effective height advantage over their prey.     

Aerial hunting behaviour and predation success by peregrine falcons Falco peregrinus on starling flocks Sturnus vulgaris

Predators use diverse hunting strategies to maximize hunting success, while preys adopt anti‐predator strategies to maximize escape chances, among which flocking, communal roosting, and the related collective responses are a common pattern in gregarious species. Prey‐predator interactions involving a single predator and flocks, a common situation in birds, have received little attention. We studied predation behaviour and success of peregrine falcons Falco peregrinus on starlings Sturnus vulgaris, a highly gregarious species, in proximity of two winter roosts. A total of 328 hunting sequences, with an overall success of 23.1% were recorded. They usually consisted of several attacks, predation success being higher when hunting sequences lasted less than 1.5 min, included less than 3 attacks and no other falcons were hunting simultaneously. Predation success was higher when hunts were directed on singletons than on flocks. However, most hunting sequences were directed towards flocks. Nine hunting strategies on flocks were identified. The most frequent was the ‘surprise attack’, which was also the most successful. We suggest that this strategy minimizes the amount of anti‐predator display elicited by flocks and economizes energy spent in hunting. The constant predation pressure did not seem to affect the use of roosts by starlings, consistent with the ‘dilution’ hypothesis, while falcons captured at least one prey item every evening. Communal roosting may benefit predator and prey, as both sides could have reached a mutual local equilibrium.     

Surprise as a winter hunting strategy in Sparrowhawks Accipiter nisus,Peregrines Falco peregrinus and Merlins F. columbarius

Sparrowhawks Accipiter nisus, Peregrines Falco peregrinus and Merlins Falco columbarius were studied hunting Redshanks Tringa totanus, Dunlins Calidris alpina and Skylarks Alauda arvensis over three winters on a small Scottish estuary. Most Sparrowhawk and Merlin hunts consisted of a single attack (mean = 1.0 and 1.1, respectively), whereas Peregrine hunts often consisted of several attacks (mean = 1.8). Most hunts were short (<1 min), but Peregrine and Merlin hunts occasionally lasted over 5 min. In general, all three raptor species attacked by surprise, although Peregrines were more likely to make nonsurprise attacks. Prey attacked were usually initially very close to the raptor (<100 m); Peregrines attacked prey most often at long distances (>500 m). Chase lengths were mostly <5 second in length, although Peregrines, and particularly Merlins hunting Skylarks, often chased for several minutes. Peregrines attacked most prey in flight from flight, while Merlins and Sparrowhawks attacked birds on the ground with a flight from a perch. All three raptor species preferentially attacked larger Dunlin flocks, but Peregrines also favoured single birds. Capture rates of Redshanks and Dunlins were similar for the three raptor species (C. 10%), but for Skylarks, capture rate by Merlins was much higher (12%) than by Sparrowhawks (3%) or Peregrines (0%). Capture rates were highest when raptors attacked by surprise, particularly for a Peregrine hunting in the first minute of arrival on the study site if no Peregrines had been hunting there for the previous hour (16% success for the first minute compared with 2% in subsequent minutes). Sparrowhawks were more successful when attacking small rather than large Dunlin flocks. The use of short surprise attacks interspersed with long periods of inactivity was common to the three raptor species and was interpreted as a strategy to minimize the amount of energy and risk involved in hunting during the nonbreeding season.     

Evolution of reversed sexual size dimorphism and role partitioning among predatory birds, with a size scaling of flight performance

To explain the adaptive significance of sex role partitioning and reversed sexual size dimorphism among raptors, owls and skuas, where females are usually larger than males, we combine several previous hypotheses with some new ideas. Owing to their structural and behavioural adaptations for prey capture, predatory birds have better prospects than other birds of defending their offspring against nest predators. This makes sex role partitioning advantageous; one parent guards the offspring while the other forages for the family. Further, among predators hunting alert prey such as vertebrates, two mates because of interference may not procur much more food than would one mate hunting alone. By contrast, two mates feeding on less alert prey may together obtain almost twice as much food as one mate hunting alone. For these reasons, partitioning of breeding labours might be adaptive only in predatory birds. An initial imbalance favours female nest guarding and male foraging: the developing eggs might be damaged if the female attacks prey; their mass might reduce her flight performance; she must visit the nest to lay; and the male feeds her before she lays (‘courtship feeding’). Increased female body size should enhance egg production, incubation, ability to tear apart prey for the young, and, in particular, offspring protection in predatory birds. Efficient foraging during the breeding period then becomes most important for the male. This imposes great demands on aerial agility in males, particularly among predators of agile prey. Flight performance decreases with increasing size in five of six aspects explored. The male must therefore not be too large in relation to the most important prey. For these reasons, he should be smaller than the female. Among predatory birds, size dimorphism increases with the proportion of birds in the diet, which may be explained as follows. Adult birds have mainly one type of predators: other predatory birds. Because almost only these specialists exploit adult birds, they carry out most of the cropping of this prey. A predator of easier prey competes with many other kinds of predators, which considerably reduce prey abundance in its territory. This is not so for predators of adult birds. Further, because birds are extremely agile, the specialized predator can hunt efficiently only within a limited size range of birds, whose flight skill it can match. Increased size dimorphism among these predators therefore should be particularly important for enlarging the combined food base of the pair. A bird specialist may consume much of the available prey in the suitable size range during the breeding period. When the predator's young are large enough to defend themselves, the female aids better by hunting than by guarding the chicks. It is advantageous among bird specialists if she hunts prey of other sizes than does the male, who has by then reduced prey abundance in his prey size class. But among predatory birds hunting easier prey the female gains little by hunting outside the male's prey spectrum, because other kinds of predators will have reduced the prey abundance outside as well as inside the male's preferred size range. Intra-pair food separation through large sexual size dimorphism therefore should be particularly advantageous among predators of birds. This may be the main reason why the degree of size dimorphism increases with the dietary proportion of birds.     

Vertebrate Predation and Food-Sharing in Cebus and Pan

Capuchins and chimpanzees are the only nonhuman primates apart from baboons known to prey systematically upon relatively large vertebrates. Vertebrate predation is common and well documented in Pan troglodytes, rare in Pan paniscus, and commonly reported but infrequently studied in Cebus. Food-sharing is common in both Pan species but rarely reported for wild capuchins. I present data on vertebrate predation and food-sharing by white-faced capuchins (Cebus capucinus) from ongoing field studies at Santa Rosa National Park, Costa Rica. We have observed 106 successful predation events resulting in the capture of 156 prey items during 2929 observation hr (5.35 prey per 100 hr). Squirrels and nestling coatis comprised half of the prey taken; the remainder were mainly nestling birds and eggs. Adult males took 52% of all prey and 67% of squirrels. Squirrels are actively hunted and about 65% of them are adults. I estimated that the average capuchin group kills 43–50 squirrels annually, mostly during the dry season. Capuchins hunt squirrels in groups 81% of the time, and 17% of hunts are successful. There is no evidence for cooperative hunting, but occasional collaboration is suggested. Rates of food-sharing were low (1.7 per 100 hr), and meat was the only food shared between adults. I compare predation and food-sharing in C. capucinus with published data for Pan troglodytes, primarily in Gombe and Taï National Parks. I discuss sex differences, hunting strategies, the relationship between hunting and food-sharing, and various ecological and social factors that may promote vertebrate predation in Pan and Cebus.     

Predator versus prey: on aerial hunting and escape strategies in birds

Predator and prey attack-escape performance is likely to bethe outcome of an evolutionary arms race. Predatory birds aretypically larger than their prey, suggesting different flightperformances. We analyze three idealized attack-escape situationsbetween predatory and prey birds: climbing flight escape, horizontalspeeding, and turning and escape by diving. Generally a smallerbird will outclimb a larger predator and hence outclimbing shouldbe a common escape strategy. However, some predators such asthe Eleonora's falcon (Falco elenorae) has a very high rateof climb for its size. Prey species with an equal or highercapacity to climb fast, such as the swift Apus apus, usuallyadopt climbing escape when attacked by Eleonora's falcons.To analyze the outcome of the turning gambit between predatorand prey we use a Howland diagram, where the relative lineartop speeds and minimum turning radii of prey and predator definethe escape and danger zones. Applied to the Eleonora's falconand some potential prey species, this analysis indicates thatthe falcon usually wins against the example prey species; thatis, the prey will be captured. Level maneuvering hunting isthe most common strategy seen in Eleonora's falcons. To avoidcapture via use of this strategy by a predator, the prey shouldbe able to initiate tight turns at high linear speed, whichis facilitated by a low wing loading (weight per unit of wingarea). High diving speed is favored by large size. If close enough to safe cover, a prey might still opt for a verticaldive to escape in spite of lower terminal diving speed thanthat of the predator. On the basis of aerodynamic considerationswe discuss escape flight strategies in birds in relation tomorphological adaptations.     

THE SOCIABLE WEAVER,PART 4: PREDATORS,PARASITES AND SYMBIONTS

Maclean, G. L. 1973. The Sociable Weaver, Part 4: Predators, parasites and symbionts. Ostrich 44: 241–253.

The main nest predator of the Sociable Weaver in the Kalahari sandveld is the Cape Cobra Nala nivea. This snake causes great losses of eggs and chicks; one cobra may eat the contents of an entire nest mass at one feed. Another nest predator which causes smaller losses of eggs and chicks but great destruction to the nest masses is the Honey Badger Mellivora capensis. These are the only two nest predators on the Sociable Weaver in the study area. Predators on adult Sociable Weavers include several birds of prey and some small carnivorous mammals.

Adult Sociable Weavers have few ectoparasites and hardly any Mallophaga. A common ectoparasite on the legs of chicks is a blood-sucking Dermestes larva, which appears not to be harmful. The only endoparasite found was the nematode, Diplotriaena ozouxi, which infected the abdominal air sacs of the adults.

The nest material of the Sociable Weavers' communal nest masses was inhabited by a wealth of invertebrate animals and a few harmless reptiles such as skinks and geckos.

Some of the chambers in a Sociable Weaver nest mass may be taken over by other species of birds. Most of these, such as Redheaded Finches Amadina erythrocephala, use the chambers for breeding purposes only, but the most important avian symbiont, the Pygmy Falcon Polihierax semitorquatus, is a permanent resident in the chambers. The presence of Pygmy Falcons is resented by the weavers but the falcons may help to keep snakes away from the nest mass. Adult Sociable Weavers are not normally preyed on by Pygmy Falcons, although the falcons may occasionally take young weavers in the nest chambers.

The tops of the nest masses may be used as nest sites by the Giant Eagle Owl Bubo lacteus. Barn Owls Tyto alba may use cavities in the superstructure of nest masses for roosting in. Neither of these owls appeared to prey on the weavers.     

Dietary shifts,niche relationships and reproductive output of coexisting Kestrels and Long-eared Owls

Summary Food samples of breeding Kestrels (Falco tinnunculus) and Long-eared Owls (Asio otus) were collected in the peak and low phase of their preferred prey (Microtus voles) in western Finland. Diets of pairs that bred as neighbours (1 km) with interspecifics were compared with those of non-neighbours. In both species, neighbouring pairs fed less on Microtus voles and more on alternative prey than did non-neighbours. Competition theory predicts that diet overlap should be lower during prey shortage and that diet similarity should be especially reduced in neighbouring pairs. Observations were consistent with expectations: diet similarity was lower in the low vole years and neighbouring pairs showed less diet overlap that non-neighbours. Differences in habitat composition and prey availability at the sample sites should not confuse the results. In addition to the high diet similarity, hunting habitats and nest sites of the species overlapped almost completely; they only showed clear temporal segregation in hunting. Probably because of food competition, the neighbouring pairs of both species produced significantly fewer young than the non-neighbours. These results contrast with the view that the diet composition and dietary shift of rodent-feeding predatory birds can be interpreted in terms of simple opportunistic foraging. In the breeding season, interspecific competition for food seems to be an important factor that affects the niches of these species, especially in northern areas, where the seasonal low phase of voles in spring and the number of alternative prey are lower than in more southern areas.     

Lionfish predators use flared fin displays to initiate cooperative hunting

Despite considerable study, mystery surrounds the use of signals that initiate cooperative hunting in animals. Using a labyrinth test chamber, we examined whether a lionfish, Dendrochirus zebra, would initiate cooperative hunts with piscine partners. We found that D. zebra uses a stereotyped flared fin display to alert conspecific and heterospecific lionfish species Pterois antennata to the presence of prey. Per capita success rate was significantly higher for cooperative hunters when compared with solitary ones, with hunt responders assisting hunt initiators in cornering the prey using their large extended pectoral fins. The initiators would most often take the first strike at the group of prey, but both hunters would then alternate striking at the remaining prey. Results suggest that the cooperative communication signal may be characteristic to the lionfish family, as interspecific hunters were equally coordinated and successful as intraspecific hunters. Our findings emphasize the complexity of collaborative foraging behaviours in lionfish; the turn-taking in strikes suggests that individuals do not solely try to maximize their own hunting success: instead they equally share the resources between themselves. Communicative group hunting has enabled Pteroine fish to function as highly efficient predators.     

Landscape heterogeneity drives intra‐population niche variation and reproduction in an arctic top predator

While intra‐population variability in resource use is ubiquitous, little is known of how this measure of niche diversity varies in space and its role in population dynamics. Here we examined how heterogeneous breeding environments can structure intra‐population niche variation in both resource use and reproductive output. We investigated intra‐population niche variation in the Arctic tundra ecosystem, studying peregrine falcon (Falco peregrinus tundrius, White) breeding within a terrestrial‐marine gradient near Rankin Inlet, Nunavut, Canada. Using stable isotope analysis, we found that intra‐population niches varied at the individual level; we examined within‐nest and among‐nest variation, though only the latter varied along the terrestrial‐marine gradient (i.e., increased among‐nest variability among birds nesting within the marine environment, indicating higher degree of specialization). Terrestrial prey species (small herbivores and insectivores) were consumed by virtually all falcons. Falcons nesting within the marine environment made use of marine prey (sea birds), but depended heavily on terrestrial prey (up to 90% of the diet). Using 28‐years of peregrine falcon nesting data, we found a positive relationship between the proportion of terrestrial habitat surrounding nest sites and annual nestling production, but no relationship with the likelihood of successfully rearing at least one nestling reaching 25 days old. Annually, successful inland breeders raised 0.47 more young on average compared to offshore breeders, which yields potential fitness consequences for this long‐living species. The analyses of niche and reproductive success suggest a potential breeding cost for accessing distant terrestrial prey, perhaps due to additional traveling costs, for those individuals with marine nest site locations. Our study indicates how landscape heterogeneity can generate proximate (niche variation) and ultimate (reproduction) consequences on a population of generalist predator. We also show that within‐individual and among‐individual variation are not mutually exclusive, but can simultaneously arise and structure intra‐population niche variation.     

Red-tailed monkeys (Cercopithecus ascanius) hunt green pigeons (Treron calva) in the Kalinzu Forest in Uganda

Red-tailed monkeys (Cercopithecus ascanius) were observed hunting green pigeons (Treron calva) in the Kalinzu Forest in Uganda. During 2 h 39 min, I observed two cases of successful hunting and one case of unsuccessful hunting in a Ficus saussureana tree. Red-tailed monkeys stalked the pigeons until they were within 2–3 m, and then jumped and caught them. In both successful cases, blue monkeys (C. mitis) ran to the hunting site from adjacent trees in order to poach the prey, and the red-tailed monkeys fled. One of these red-tailed monkeys dropped the pigeon while fleeing, and the blue monkey climbed down from the tree to search for it. This is the first record of cercopithecoid monkeys hunting birds that are outside of the nest and moving freely, and also the first record of red-tailed monkeys hunting vertebrates. However rare it may be, the repeated hunting attempts using similar techniques and the immediate attempt of blue monkeys to poach the prey suggest that this type of hunting was not a one-time event that happened by chance. Blue monkeys and an adult chimpanzee (Pan troglodytes schweinfurthii) in and around the fig tree did not attempt to hunt. The hunting of volant birds may be enabled by the small body size and the quick movements of red-tailed monkeys.     

Translocation of threatened New Zealand falcons to vineyards increases nest attendance, brooding and feeding rates

Anthropogenic landscapes can be rich in resources, and may in some cases provide potential habitat for species whose natural habitat has declined. We used remote videography to assess whether reintroducing individuals of the threatened New Zealand falcon Falco novaeseelandiae into a highly modified agricultural habitat affected the feeding rates of breeding falcons or related breeding behavior such as nest attendance and brooding rates. Over 2,800 recording hours of footage were used to compare the behavior of falcons living in six natural nests (in unmanaged, hilly terrain between 4 km and 20 km from the nearest vineyard), with that of four breeding falcon pairs that had been transported into vineyards and nested within 500 m of the nearest vineyard. Falcons in vineyard nests had higher feeding rates, higher nest attendance, and higher brooding rates. As chick age increased, parents in vineyard nests fed chicks a greater amount of total prey and larger prey items on average than did parents in hill nests. Parents with larger broods brought in larger prey items and a greater total sum of prey biomass. Nevertheless, chicks in nests containing siblings received less daily biomass per individual than single chicks. Some of these results can be attributed to the supplementary feeding of falcons in vineyards. However, even after removing supplementary food from our analysis, falcons in vineyards still fed larger prey items to chicks than did parents in hill nests, suggesting that the anthropogenic habitat may be a viable source of quality food. Although agricultural regions globally are rarely associated with raptor conservation, these results suggest that translocating New Zealand falcons into vineyards has potential for the conservation of this species.     

BREEDING BEHAVIOUR OF OSPREYS PANDION HALIAETUS IN SCOTLAND

Ospreys Pandion haliaetus nested at a site near Loch Garten, Inverness-shire continuously from 1959 to 1973. Each year the Royal Society for the Protection of Birds has organized a continuous watch on the eyrie in the breeding season. The detailed records kept of the activities of Ospreys at the nest by those participating in the watch were analysed and the results presented here. Ospreys are migratory and arrived in the breeding area in early April. Nesting material was usually added to an existing eyrie platform. The male collected more material than the female. The female lined the nest cup. The extent of nest building activity and the frequencies of mating and other activities prior to laying varied markedly from year to year. These differences may have been related to changes in the identity of the nesting female, but the birds were not individually marked. Both sexes incubated but the female took the greater share and normally incubated at night. When the young hatched they were brooded by the female. The female stayed in the vicinity of the nest for most of the time until the young fledged at about 53 days old. The male Osprey caught almost all the fish eaten by his mate and young during the breeding season. The number of fish caught per day increased markedly after the young hatched. Pike Esox lucius and Trout Salmo trutta were the main species taken, and some Rainbow Trout Salmo gairdnerii were identified. There were seasonal and diurnal changes in the size and the species composition of the catch. The effects of weather conditions on hunting are examined. The occurrence of Ospreys other than the resident birds at the nest site is described. The behaviour of another pair of Ospreys which repeatedly failed to hatch eggs is described. There was an instance of egg eating in this pair, and some differences in behaviour were found between these birds and those at Loch Garten whose breeding success was good. The breeding biology of Ospreys is compared with that of other British diurnal birds of prey. In other species the female leaves the young unguarded at some stage in the nestling period and hunts food for them, whereas female Ospreys do not usually hunt in the nesting period.     

Evidence of prey depletion around lesser kestrel Falco naumanni colonies and its short term negative consequences

Predation may reduce prey numbers in such extent that prey may be depleted, which has negative effects on predator populations. Prey depletion would be more likely when the number of predators increase and/or concentrate their activity in a certain area, as is the case of colonial birds. As a matter of fact, food depletion due to intraspecific competition is considered a major cost of coloniality, and several studies have shown indirect evidence of this. However, no direct measures of food depletion have been provided along with its consequences for the fitness of the colony inhabitants. We carried out a field study with the lesser kestrel Falco naumanni, a raptor that breeds in colonies ranging from two to dozens of pairs. During the nestling period we sampled the main prey of the kestrels around different sized colonies at increasing distances. At the same time, we recorded hunting distances and prey delivery rates to the nest. In addition, we monitored the reproductive success in colonies of different sizes. Lesser kestrels feed their nestlings mainly with grasshoppers and these prey became depleted through the season in the surroundings of the large colonies. Prey depletion made kestrels fly longer distances to forage and prey delivery rates to the nest decreased. Lower feeding rates were not compensated by bringing larger prey, hence, the net amount of energy provided to the chicks decreased with the date in large colonies. By contrast, none of this occurred around small colonies, where both prey abundance and hunting distance remained constant throughout the season. As a consequence, the seasonal decline in the reproductive success (number of fledglings and fledgling body condition) was greater the larger the colony. Thus, these results evidence that food depletion and its fitness costs are related to colony size, as they are suffered by the kestrels breeding in large colonies but not by those settled at small ones. Finally, the consequences of prey depletion on the demographic dynamics and the regulation of colony size are discussed.     

Behavioral responses of male elk to hunting risk

Prey respond to predation risk with a range of behavioral tactics that can vary based on space use and hunting mode of the predator. Unlike other predators, human hunters are often more spatially and temporally restricted, which creates a period of short-duration, high-intensity predation risk for prey. Consequently, identifying the roles different hunting modes (i.e., archery and rifle), hunts for targeted and non-targeted species, and landscape features play in altering spatial and temporal responses of prey to predation risk by humans is important for effective management of harvested populations. From 2009 to 2016, we used a large-scale experiment including 50 animal-years of location data from 38 unique male elk (Cervus canadensis) to quantify changes in movement and resource selection in response to hunters during 3 separate 5-day controlled hunts for antlered males (elk archery, deer [Odocoileus spp.] rifle, and elk rifle) at the Starkey Experimental Forest and Range in northeast Oregon, USA. We evaluated competing hypotheses regarding elk responses to varying levels of prey risk posed by the different hunt types. We predicted that the strength of elk behavioral responses would increase with perceived hunter lethality (i.e., weak response to elk archery but similar response to elk and deer rifle hunts) and that prey response would be closely associated with hunter activity within the diel cycle (greater during diurnal than nocturnal hours) and across hunting seasons. Elk responses were strongest during diurnal hours when hunters were active on the landscape and were generally more pronounced during both rifle hunts than during the archery hunt (supporting our perceived lethality hypothesis). Male elk avoided open roads across all periods except during nocturnal hours of the breeding season and alternated between avoidance of areas with high canopy cover during nocturnal hours and selection during diurnal hours. In combination these patterns led to distinct distributional changes of male elk from pre-hunt to hunt periods. Patterns of male elk selection highlight the importance of managing for heterogeneous landscapes to meet a variety of habitat, harvest, hunter satisfaction, and escapement objectives.     

Hunting and Occasional Consumption of Prey Items by Chimpanzees at the Primate Foundation of Arizona

Researchers have documented hunting by wild chimpanzees (Pan troglodytes) for >30 yr. However, no one had reported the behavior in captive chimpanzees. The Primate Foundation of Arizona (PFA) is a biomedical research facility, and though every effort is made to ensure that rodents and other indigenous animals do not enter cages, an occasional small mammal or bird enters the outside cage area. We document 18 known successful hunts over 2.5 yr by ≥8 captive chimpanzees housed at PFA. The most common prey were rock squirrels (Cittallus variegatus; n = 8) and birds (n = 7). The most common killing method was a bite to the head (n = 9), indicating that the deaths were deliberate and not accidental. Two adult males, 1 wild- and 1 captive-born, together accounted for 11 of the 18 hunting episodes. The chimpanzees generally captured and killed the prey in their outdoor enclosures. The results have implications for the surveillance of outdoor areas in other facilities and the potential for disease or introduction of parasitic vectors, and are also an interesting comparison to wild chimpanzee behavior.     

Olfactory eavesdropping: The odor of feathers is detectable to mammalian predators and competitors

The role of olfactory eavesdropping in interactions between mammalian predator and prey species is well established. Bird plumage can be odorous and consequently nest predators could use odor to identify and locate avian prey, and nest competitors could use odor to assess occupancy of nest cavities by birds. However, despite extensive research on avian nest predation and competition, the costs of olfactory eavesdropping on plumage odor by nest predators or competitors remain largely unknown. We used two experiments to investigate whether feather odor is detected by marsupial species which are competitors for nest hollows and predators of eggs and nestlings of crimson rosellas, Platycercus elegans. In the first experiment, odor presentation at nest boxes utilized by ringtail possums (Pseudocheirus peregrinus) and rosellas showed that the latency of possums to enter the nest was shorter when crimson rosella odor was present compared to the controls. In the second experiment, carried out away from nest hollows, brushtail possums (Trichosurus vulpecula) discriminated odors of two predators (dingo, Canis lupus dingo, and cat, Felis catus) from crimson rosella and control odors; however, they did not discriminate between crimson rosella odor and a control. We show that marsupials may use feather odor cues to assess nest hollow status, information which could aid their detection of avian prey or their vigilance at nest hollows (for which they compete with parrots). To our knowledge, our study is the first to show that wild mammalian predators and competitors of birds respond to plumage odor at nests and suggest that odor signaling may have hitherto unrecognized costs for birds.     

Interspecific communicative and coordinated hunting between groupers and giant moray eels in the Red Sea

Intraspecific group hunting has received considerable attention because of the close links between cooperative behaviour and its cognitive demands. Accordingly, comparisons between species have focused on behaviours that can potentially distinguish between the different levels of cognitive complexity involved, such as “intentional” communication between partners in order to initiate a joint hunt, the adoption of different roles during a joint hunt (whether consistently or alternately), and the level of food sharing following a successful hunt. Here we report field observations from the Red Sea on the highly coordinated and communicative interspecific hunting between the grouper, Plectropomus pessuliferus, and the giant moray eel, Gymnothorax javanicus. We provide evidence of the following: (1) associations are nonrandom, (2) groupers signal to moray eels in order to initiate joint searching and recruit moray eels to prey hiding places, (3) signalling is dependent on grouper hunger level, and (4) both partners benefit from the association. The benefits of joint hunting appear to be due to complementary hunting skills, reflecting the evolved strategies of each species, rather than individual role specialisation during joint hunts. In addition, the partner species that catches a prey item swallows it whole immediately, making aggressive monopolisation of a carcass impossible. We propose that the potential for monopolisation of carcasses by one partner species represents the main constraint on the evolution of interspecific cooperative hunting for most potentially suitable predator combinations.     

Hunting Behavior of Chimpanzees at Ngogo,Kibale National Park,Uganda

Chimpanzees (Pan troglodytes) prey on a variety of vertebrates, mostly on red colobus (Procolobus spp.) where the two species are sympatric. Variation across population occurs in hunting frequency and success, in whether hunting is cooperative, i.e., payoffs to individual hunters increase with group size, and in the extent to which hunters coordinate their actions in space and time, and in the impact of hunting on red colobus populations. Also, hunting frequency varies over time within populations, for reasons that are unclear. We present new data on hunting by chimpanzees at Ngogo, Kibale National Park, Uganda, and combine them with earlier data (Mitani and Watts, 1999, Am. J. Phys. Anthropol. 109: 439–454) to examine hunting frequency and success, seasonality, and cooperation. The Ngogo community is the largest and has the most males of any known community. Chimpanzees there mostly hunt red colobus and are much more successful and make many more kills per hunt than at other sites; they kill 6–12% of the red colobus population annually. The number of kills and the offtake of meat per hunt increase with the number of hunters, but per capita meat intake is independent of hunting party size; this suggests that cheating occurs in large parties. Some behavioral cooperation occurs. Hunting success and estimated meat intake vary greatly among males, partly due to dominance rank effects. The high overall success rate leads to relatively high average per capita meat intake despite the large number of consumers. The frequency of hunts and of hunting patrols varies positively with the availability of ripe fruit; this is the first quantitative demonstration of a relationship between hunting frequency and the availability of other food, and implies that the chimpanzees hunt most when they can easily meet energy needs from other sources. We provide the first quantitative support for the argument that variation in canopy structure influences decisions to hunt red colobus because hunts are easier where the canopy is broken.     

Concealed by darkness: interactions between predatory bats and nocturnally migrating songbirds illuminated by DNA sequencing

Recently, several species of aerial‐hawking bats have been found to prey on migrating songbirds, but details on this behaviour and its relevance for bird migration are still unclear. We sequenced avian DNA in feather‐containing scats of the bird‐feeding bat Nyctalus lasiopterus from Spain collected during bird migration seasons. We found very high prey diversity, with 31 bird species from eight families of Passeriformes, almost all of which were nocturnally flying sub‐Saharan migrants. Moreover, species using tree hollows or nest boxes in the study area during migration periods were not present in the bats’ diet, indicating that birds are solely captured on the wing during night‐time passage. Additional to a generalist feeding strategy, we found that bats selected medium‐sized bird species, thereby assumingly optimizing their energetic cost‐benefit balance and injury risk. Surprisingly, bats preyed upon birds half their own body mass. This shows that the 5% prey to predator body mass ratio traditionally assumed for aerial hunting bats does not apply to this hunting strategy or even underestimates these animals’ behavioural and mechanical abilities. Considering the bats’ generalist feeding strategy and their large prey size range, we suggest that nocturnal bat predation may have influenced the evolution of bird migration strategies and behaviour.