Nocturnal Predators Research Articles

Sleeping Tree Selection of Cao Vit Gibbon (Nomascus nasutus) Living in Degraded Karst Forest in Bangliang, Jingxi, China

We studied the sleep-related behavior of two Cao Vit gibbon (Nomascus nasutus) groups in Bangliang Nature Reserve in Jingxi County, China between January 2008 and December 2009 to test four hypotheses related to sleeping tree selection (predation avoidance, thermoregulation, food access, and range defense). Gibbons entered sleeping trees 88 ± SD 37 min before sunset before their main potential nocturnal predator become active. They usually moved rapidly and straight to sleeping trees and kept silent once settled. Over the course of the study, gibbon groups used many (87 and 57 per group) sleeping trees and reused them irregularly. They also tended to sleep in relatively tall trees without lianas, choosing small branches close to the treetop. These behaviors would make it difficult for potential terrestrial predators to detect and approach the gibbons. Therefore, these results strongly support the predation avoidance hypothesis. Gibbons tended to sleep closer to ridges than to valley bottoms and they did not sleep at lower elevations in colder months. They thus appeared not to select sleeping trees to minimize thermoregulatory stress. Gibbons very rarely slept in feeding trees, instead generally sleeping more than 100 m away from the last feeding trees of the day or the first feeding tree of the next morning. These patterns led us to reject the food access hypothesis. Lastly, we did not find evidence to support the range defense hypothesis because gibbons did not sleep in overlap areas with neighbors more often than expected based on the proportion of overlap and exclusively used areas.

Evolutionary Approach Highly Informative but Should Not Be Overstated

Dear Editor: I thank The CJP for its thought-provoking issue examining evolutionary explanations for mental illness and, in particular, Dr Edward H Hagen's fascinating article on depression.1 My patients often find it helpful when their symptoms are presented within an evolutionary context as adaptive mechanisms that are malfunctioning in some way. However, one issue I would like to call attention to is that significant evolutionary change in humans occurs on large time scales (that is, many generations or millennia).2 Therefore, it is plausible that current behaviours appearing to be maladaptive were adaptive for our ancestors tens of thousands of years ago but may no longer be useful for modern life. A trivial example would be children's fear of the dark, which may have protected them from nocturnal predators in ages past but currently serves only to make bedtime more difficult. Let us examine the 2 behaviours that Dr Hagen highlights as possibly adaptive - excessive rumination and suicidality in response to a Stressor. Ruminating about a problem until a solution presents may have been a relatively straightforward process in our ancestors whose cognitive sophistication and options for addressing problems were much more limited than our own. In contrast, presentday patients with depression can end up in complicated, often futile ruminative cycles that are actively counterproductive. Regarding suicidality, one might imagine that an aggressive response to a Stressor could have been adaptive for earlier humans fighting for social status or resources. Suicidality may represent this kind of aggression maladaptively turned inwards. Excessive rumination and suicidality are serious, debilitating symptoms with the latter potentially fatal. It seems at least as likely that they reflect a mismatch between the needs of modern humans and those of our recent ancestors than behaviours that should be considered healthy or adaptive at present. On a separate note, Dr Hagen is absolutely correct that depression may represent a cry for help and that we need to do a better job of addressing its precipitants. But even if it has adaptive underpinnings, depression is clearly a source of true suffering and its theoretically adaptive value is an insufficient argument for withholding antidepressants or other treatments that may provide relief. Even if it has adaptive origins, we are not going to stop treating suicidality. We need to be careful to use evolutionary theory for its capacity to explain human behaviour rather than as a source of normative ethics. As scientists, we can certainly work toward understanding the use of some depressive symptoms, but as healers, when patients come to us for help, we must also seek to alleviate their suffering, adaptive or not.

Survival and population persistence in the critically endangered Tuamotu kingfisher

AbstractA wide range of threats affect populations of Pacific island birds and conservationists have been challenged to identify factors upon which to focus management. The Tuamotu kingfisher (Todiramphus gambieri) is one of the most endangered vertebrate species in the world, yet little has been published about basic biology or causes of the population decline. We used 4 years of mark‐resight and territory resource information to model survival in juvenile and adult Tuamotu kingfishers. Annual survival of adult males (ϕ = 0.77) was similar to congeneric species, whereas survival of adult females (ϕ = 0.40) and juveniles (ϕ = 0.12) was much lower. The best‐supported survival model indicated adult female survival was positively related to territory size, whereas adult male survival was negatively related to atoll forest within territories. We used parameter estimates from survival models in a life‐stage simulation analysis to evaluate the relative influence of vital rates and territory habitats on population processes. Results indicated that adult female and juvenile survival had the greatest impact on Tuamotu kingfisher populations, accounting for 58% and 32% of variation in the finite rate of population increase, respectively. Nocturnal predation by rats (Rattus spp.) on incubating kingfishers may explain the lower survival of females than males, whereas juvenile birds may be especially vulnerable to predation by cats (Felis catus). Thus, conservation management for Tuamotu kingfishers should include use of metal guards on cavity trees to protect nests and incubating females, and control predator access during fledging periods. © 2012 The Wildlife Society.

Exceptionally preserved fossil insect ears from the Eocene Green River Formation of Colorado

Tympanal ears in insects are important for both intraspecific communication and for the detection of nocturnal predators. Ears are thought, based on modern forms, to have originated independently multiple times within insects and can be found on multiple regions of the body. Here we describe and document the exceptionally well preserved tympanal ears found in crickets and katydids from the Eocene Green River Formation of Colorado, which are virtually identical to those seen in modern representatives of these groups. These specimens are among the best preserved insect ears in the fossil record and establish the presence of ears in two major clades of Orthoptera 50 million years ago. Also discussed and evaluated are previously described insect ears from the Mesozoic and the implications of the findings of the present study for studying the evolution of ears within insects.

Overnight foraging trips by chick‐rearing Nazca Boobies Sula granti and the risk of attack by predatory fish

Most tropical booby species complete breeding foraging trips within daylight hours, thus avoiding nights at sea. Nazca Boobies Sula granti are unusual in this respect, frequently spending one or more nights away from the nest. We used GPS dataloggers, time‐depth recorders, and changes in body weight to characterize foraging trips and to evaluate potential influences on the decisions of 64 adult Nazca Boobies to spend a night at sea, or to return to their chicks on Isla Española, Galápagos, in daylight hours. The tagged birds foraged east of Isla Española, undertaking both single‐day (2–15 h, 67% of trips) and overnight trips (28 h–7.2 days, 33%), and executing 1–19 foraging plunge‐dives per single‐day trip. Birds might forage longer if they are in nutritional stress when they depart, but body weight at departure was not correlated with trip length. Birds might be expected to return from longer trips with more prey for young, but they returned from single‐day and overnight trips with similar body weights, consistent with previous indications that Nazca Boobies forage until accumulating a target value of prey weight. Birds with a lower dive frequency during the first 5 h of a trip were more likely to spend the night at sea, suggesting that they might choose to spend the night at sea if prey capture success was low. At night, birds almost never dived and spent most of their time resting on the water’s surface (11.8–12.1 h, > 99% of the time between civil sunset and civil dawn). Thus, the night is an unproductive time spent among subsurface predators under low illumination. The birds’ webbed feet provided evidence of this risk: 24% of birds were missing > 25% of their foot tissue, probably due to attacks by predatory fish, and the amount of foot tissue lost increased with age, consistent with a cumulative risk across the lifespan. In contrast, other tropical boobies (Blue‐footed Sula nebouxii and Brown Boobies Sula leucogaster), which do not spend the night on the water, showed no such damage. These results suggest that chick‐rearing Nazca Boobies accept nocturnal predation risk on occasions of low prey encounter during a foraging trip’s first day.

The difference between night and day: antipredator behavior in birds

Animals have evolved sophisticated strategies for avoiding predators during the day. These strategies can vary depending on the type of predator and level of threat. Although nocturnal predation is a major cause of animal mortality, antipredator behavior at night is poorly under- stood. To investigate how diurnal animals adjust their anti- predator behavior during these different conditions, peahens (Pavo cristatus) were exposed to a taxidermy raccoon during the daytime and nighttime. During the day, the peahens emitted loud antipredator calls, extended their necks upward, adopted a preflight posture, and approached the predator; at night, the peahens emitted soft hissing calls, remained sta- tionary, piloerected their feathers, and raised their tails. The results demonstrate that birds adopt radically different anti- predator behavior depending on whether the threat occurs in the daytime or nighttime. These different tactics could result from limitations in sensory abilities. Videos showing noc- turnal and diurnal antipredator behavior of peafowl are available online (http://www.momo-p.com/showdetail-e. php?movieid=momo111110pc01a and http://www.momo- p.com/showdetail-e.php?movieid=momo111110pc02a).

Sleeping birds do not respond to predator odour.

BackgroundDuring sleep animals are relatively unresponsive and unaware of their environment, and therefore, more exposed to predation risk than alert and awake animals. This vulnerability might influence when, where and how animals sleep depending on the risk of predation perceived before going to sleep. Less clear is whether animals remain sensitive to predation cues when already asleep.Methodology/Principal FindingsWe experimentally tested whether great tits are able to detect the chemical cues of a common nocturnal predator while sleeping. We predicted that birds exposed to the scent of a mammalian predator (mustelid) twice during the night would not go into torpor (which reduces their vigilance) and hence would not reduce their body temperature as much as control birds, exposed to the scent of another mammal that does not represent a danger for the birds (rabbit). As a consequence of the higher body temperature birds exposed to the scent of a predator are predicted to have a higher resting metabolic rate (RMR) and to lose more body mass. In the experiment, all birds decreased their body temperature during the night, but we did not find any influence of the treatment on body temperature, RMR, or body mass.Conclusions/SignificanceOur results suggest that birds are not able to detect predator chemical cues while sleeping. As a consequence, antipredatory strategies taken before sleep, such as roosting sites inspection, may be crucial to cope with the vulnerability to predation risk while sleeping.

Generalist Predators and Predation of Black CutwormAgrotis ipsilonLarvae in Close Mown Creeping Bentgrass

Predators play a significant role in regulating pest outbreaks in turfgrass (Potter 2001). The most common predaceous arthropods recorded from turfgrass are spiders, predatory beetles (Carabidae and Staphylinidae) (Kunkel et al. 1999; Rothwell & Smitley 1999), predatory hemipterans, and ants (Lopez & Potter 2003; Frank & Shrewsbury 2004a). Natural enemies and their effects can be monitored by pitfall traps (e.g., Kunkel et al. 1999; Frank & Shrewsbury 2004a) or by exposing prey overnight without direct observation (Kunkel et al. 1999; Lopez & Potter 2000; Frank & Shrewsbury 2004a). Furthermore, most studies are conducted in roughs or fairways, which have more biodiversity (Lopez & Potter 2000), greater mowing height, and are less intensely managed than greens. Predation and predator abundance can be significantly different based on mowing heights (Rothwell & Smitley 1999). A better understanding of ecosystem services in putting greens may provide insights into reducing pesticide inputs. The objectives of this study were to determine the types of nocturnal predators in putting greens and determine which taxa are involved in predation of black cutworm larvae (Agrotis ipsilon Hufnagel) in close-mown bentgrass. Black cutworms provide a model system to investigate predation in turfgrass. Black cutworm larvae feed nocturnally on creeping bentgrass ( Agrostis stolonifera L.) greens causing pock marks that interfere with ball roll and aesthetics (Potter 1998). Predation trials were conducted at the Turfgrass Research Unit, Auburn, Alabama and the Grand National Golf Course, Opelika, Alabama. Plots or greens had not been sprayed with insecticides for at least 2 wk prior to each experiment. At the Turfgrass Research Unit, 2 plots of creeping bentgrass were used. A 706 m2 plot was used for larval predation trials, and a 929 m2 plot for predator surveys. Turfgrass in these plots was maintained at 0.33 cm with surrounding turf 2.54 cm high. Putting greens have 'Dominant' creeping bentgrass, whereas 'El Toro* zoysiagrass ( Zoysia japonica Steud), and 'Tifway' bermudagrass (Cynodon dactylon L. Pers Cynodon transvaalensis Burtt-Davy) were established in collars. Greens and collars are maintained at 0.36 and 1.27 cm, respectively. Larvae were obtained from a commercial in-

From optics to attention: visual perception in barn owls

Barn owls are nocturnal predators which have evolved specific sensory and morphological adaptations to a life in dim light. Here, some of the most fundamental properties of spatial vision in barn owls are reviewed. The eye with its tubular shape is rigidly integrated in the skull so that eye movements are very much restricted. The eyes are oriented frontally, allowing for a large binocular overlap. Accommodation, but not pupil dilation, is coupled between the two eyes. The retina is rod dominated and lacks a visible fovea. Retinal ganglion cells form a marked region of highest density that extends to a horizontally oriented visual streak. Behavioural visual acuity and contrast sensitivity are poor, although the optical quality of the ocular media is excellent. A low f-number allows high image quality at low light levels. Vernier acuity was found to be a hyperacute percept. Owls have global stereopsis with hyperacute stereo acuity thresholds. Neurons of the visual Wulst are sensitive to binocular disparities. Orientation based saliency was demonstrated in a visual-search experiment, and higher cognitive abilities were shown when the owl's were able to use illusory contours for object discrimination.

Evidence of predation and disturbance events at Heliconius (Insecta: Lepidoptera: Nymphalidae) nocturnal aggregations in Panama and Costa Rica

Many unpalatable species use conspicuous colours to give a clear signal (aposematism) to predators of their noxiousness, and in many cases the message can be strengthened through aggregations. Several species of neotropical aposematic Heliconius butterflies present an interesting case because, although they form nocturnal aggregations, the colours on their wings are not detectable at night and there are no known nocturnal predators. Müllerian mimicry is probably the most important phenomenon that makes Heliconius butterflies one of the most successful neotropical groups but many other ecological adaptations have contributed to their success. These adaptations include availability of different models, wing colour adaptation to background light, and specific diurnal flying ranges as well as exclusive nocturnal roosting height ranges for each mimicry ring. By providing nocturnal habitat segregation, but most importantly protection from nocturnal predators, Heliconius nocturnal aggregations could have evolved to contribute to the success of coexistent Müllerian mimicry rings. The present work reports for the first time evidence of nocturnal predation attempts by bats and disturbance events at Heliconius roosting sites.

Lunar and diurnal cycles in reproductive physiology and behavior in a natural population of cooperatively breeding fish

Natural environmental periodicity that occurs on both the small scale like day length, or larger scale like lunar light can provide animals with valuable information about resource availability and predation risk. Such environmental cycles are often linked to the timing of reproduction. Here, using the circulating androgen concentrations, gonadal investment patterns and detailed behavioral observations we show that wild populations of the group-living cichlid, Neolamprologus pulcher from Lake Tanganyika, have marked diurnal differences in behavior and lunar synchronicity in their reproductive physiology and behavior. Female ovarian investment peaked in the first quarter of the lunar cycle. In males, plasma steroid hormone levels and sperm swimming speed were highest at this same lunar stage, supporting the idea that egg laying occurs during this phase and that young will emerge at full moon, perhaps because nocturnal predators can be best detected then. Female subordinate group members' gonadal investment patterns mirrored the lunar pattern observed in dominant female breeders. In contrast, male subordinates did not show a change in gonadal investment or in steroid hormone concentrations across the lunar cycle, suggesting that female subordinates, but not male subordinates, reproduce within the social group. Neolamprologus pulcher demonstrated diurnal cycles in behavior, with higher rates of feeding in the morning. Male and female breeding pairs were strongly size matched potentially as a result of size-assortative mating; also the gonadal investment of male and female mated pairs was strongly correlated indicating within-pair reproductive synchronicity. In general, this study provides evidence for the impact of environmental cues (sunlight and moonlight) on circulating hormones and reproduction in a small tropical freshwater fish.

Comparative predation rates on larval snappers (Lutjanidae) in oceanic, reef, and nearshore waters

The life cycle of most reef fishes involves pelagic larvae entering the nearshore environment to settle to benthic substrates. Settlement is considered to be highly risky as larvae encounter high rates of predation mortality associated with shallow nearshore habitats. This potential bottleneck may be particularly significant for many tropical snapper (Lutjanidae) species which bypass the reef to settle to very nearshore seagrass areas. To test the hypothesis that predation-related mortality increases as naïve late-stage fish larvae leave the offshore oceanic environment and enter the nearshore to settle, relative nocturnal predation rates on tethered late-stage snapper larvae were measured in oceanic, coral reef, and nearshore surface waters of the lower Florida Keys, USA. Both relative predation rate and probability of predation in oceanic areas seaward of the reef was significantly greater than over reef or nearshore seagrass/hardbottom habitats. This surprising result may be due to differences in the density or spatial distribution of potential predators between deep offshore (near flotsam at the surface) and shallow nearshore environments (demersal). These findings suggest that successful late-stage snapper larvae should avoid surface waters in deep oceanic areas and move upward in the water column as they pass over the reef and other shallow nearshore environments prior to settlement.

Trapped in the darkness of the night: thermal and energetic constraints of daylight flight in bats

Bats are one of the most successful mammalian groups, even though their foraging activities are restricted to the hours of twilight and night-time. Some studies suggested that bats became nocturnal because of overheating when flying in daylight. This is because—in contrast to feathered wings of birds—dark and naked wing membranes of bats efficiently absorb short-wave solar radiation. We hypothesized that bats face elevated flight costs during daylight flights, since we expected them to alter wing-beat kinematics to reduce heat load by solar radiation. To test this assumption, we measured metabolic rate and body temperature during short flights in the tropical short-tailed fruit bat Carollia perspicillata at night and during the day. Core body temperature of flying bats differed by no more than 2°C between night and daytime flights, whereas mass-specific CO2 production rates were higher by 15 per cent during daytime. We conclude that increased flight costs only render diurnal bat flights profitable when the relative energy gain during daytime is high and risk of predation is low. Ancestral bats possibly have evolved dark-skinned wing membranes to reduce nocturnal predation, but a low degree of reflectance of wing membranes made them also prone to overheating and elevated energy costs during daylight flights. In consequence, bats may have become trapped in the darkness of the night once dark-skinned wing membranes had evolved.

Unique courtship and spawning behaviour in the wrinkled frog, Nyctibatrachus humayuni

AbstractFrogs of the genus Nyctibatrachus (family Nyctibatrachidae) exhibit a unique reproductive behaviour. They may completely lack or have an abbreviated amplexus, deposit terrestrial eggs and even offer paternal care. We studied the courtship and spawning behaviour of Nyctibatrachus humayuni from Matheran located in the northern region of the Western Ghats of India. The breeding season of N. humayuni coincides with the onset of south-west monsoon. Adult males vocalise from their calling sites on wet rocks/dead logs that often harbour egg clutches and females approach the calling males, resulting in a loose cephalic amplexus that lasts up to 10 minutes. The male dismounts and sits aside; then the female deposits the eggs and moves away from the spawning site or into the water. The mean clutch size and the egg diameter are found to be 30.3 ± 1.89 and 2.44 ± 0.04 mm, respectively. Once the female moves away following spawning, the male slowly moves on to the eggs and fertilises them. The males of N. humayuni appear to be territorial and offer parental care by attending the eggs only during night. Paternal egg attendance most probably reduces the risk of predation by nocturnal predators.

Predation as a driver of gastropod distribution in north-eastern New Zealand kelp forests

Gastropods play an important ecological role in kelp forests; however, this role is dependent on where exactly in such communities these animals are located. We assessed the spatial and temporal patterns in the utilisation of available reef and macroalgal substrates by three gastropods in a north-eastern New Zealand kelp (Ecklonia radiata (C. Agardh) J. Agardh, 1848) forest, focusing on predation as a factor influencing these patterns. Although kelp provided a large habitable surface area for gastropods, much of this area was under-utilised. During the day, gastropods on E. radiata were largely confined to the primary laminae. At night, gastropods on the reef migrated into the algal canopy where they occupied regions of the kelp that were not occupied during the day. Over a 36-day period, 93% of the gastropods tethered to the reef were consumed by predators, whereas none tethered in the algal canopy was consumed. We consider that night-time vertical migration and dispersion through the algal canopy may be primarily a response to predation by diurnally feeding fish and nocturnal benthic predators such as lobsters. Our research highlights the importance of considering diel changes in epifaunal distribution and abundance when assessing their ecological role.

Possible Florida Invader: Yellow Anaconda

WEC290, a 2-page illustrated fact sheet by Steve Johnson and Monica McGarrity, is part of the Florida Invaders series. It provides key information and illustrations for identifying and reporting sightings of this large, nocturnal predator that is native to tropical South America and is not established in Florida, but escaped or released pets have been encountered in the wild. Published by the UF Department of Wildlife Ecology and Conservation, September 2010.

Possible Florida Invader: Green Anaconda

WEC289, a 2-page illustrated fact sheet by Steve Johnson and Monica McGarrity, is part of the Florida Invaders series. It provides key information and illustrations for identifying and reporting sightings of this large, nocturnal predator that is native to tropical South America and is not established in Florida, but escaped or released pets have been encountered in the wild. Published by the UF Department of Wildlife Ecology and Conservation, September 2010.

Florida Invader: Burmese Python

WEC288, a 2-page illustrated fact sheet by Steve Johnson and Monica McGarrity, is part of the Florida Invaders series. It provides key information and illustrations for identifying and reporting sightings of this large nocturnal predator that is native to Southeast Asia and is now established and breeding in Florida and Puerto Rico. Published by the UF Department of Wildlife Ecology and Conservation, September 2010.

Florida Invader: African Python

WEC287, a 2-page illustrated fact sheet by Steve Johnson and Monica McGarrity, is part of the Florida Invaders series. It provides key information and illustrations for identifying and reporting sightings of this large nocturnal predator that is native to sub-Saharan Africa but may be breeding in Florida. Published by the UF Department of Wildlife Ecology and Conservation, September 2010.

Diurnal and nocturnal functional response of juvenile Notonecta maculata considered as a consequence of shifting predation behaviour

Presence or absence of light is considered to significantly affect predation within freshwater communities. In relation to light regime, the scope of the present study is to identify proximate factors accounting for different rates of predation in juvenile Notonecta maculata. It has been shown that foraging of juvenile N. maculata on Daphnia magna is reduced under dark conditions. These differences are accounted for by the presence/absence of light and are not regulated by any endogenous circadian rhythm. Direct observation of predation components revealed that in the dark, daphnid prey is detected at shorter distances, thus lowering the rate of encounter which finally results in a decreasing number of prey items eaten. Handling time was found to significantly increase during dark periods. Since the amount of food ingested per prey item increases to a certain extent with increasing handling time, it is suggested that the decreasing number of daphnids consumed is compensated by gaining a higher amount of food per item during a lengthier, more thorough, handling of the prey. A mechanistic model that describes the foraging process along a general predation cycle was parameterized based on the results of direct observations, instead of using classic functional response curves. This allows the comparison of model output to independent functional response data. A good correlation between observed and predicted data confirms the assumption that the reduction of the nocturnal predation rate is caused by shifting predation behaviour and indicates that the crucial light/dark differences in the foraging of N. maculata are considered in the approach.