Predators Research Articles

Innate response based on visual cues of sympatric and allopatric predators in Nile tilapia

Predators are an important selective pressure for prey, and responses to visual exposure to non-predators and to allopatric and sympatric predators may assist the understanding of how prey animals recognize and distinguish potential threats. Here, we visually exposed predator-naïve Nile tilapia (Oreochromis niloticus) to aquaria with only water (handling-negative control), a non-predator fish (Cyprinus carpio), a South American catfish (Pseudoplatystoma coruscans, allopatric predator), and an African catfish (Clarias gariepinus; sympatric predator). We found that Nile tilapia displayed antipredator responses to both predator catfish but not to non-predator fish or negative control conditions. These antipredator responses, however, were stronger to the sympatric catfish in comparison to the allopatric animal. We concluded that Nile tilapia is able to innately distinguish between a sympatric and an allopatric predator based on visual cues. We assume that the innate recognition of the allopatric predator could be attributed to similarities in the body morphology and movement (key stimuli) of the South American and African catfish. Although this is plausible, the mechanism of the innate allopatric recognition remains unknown and deserves future investigation.

Does color polymorphism affect the predation risk on Phalotris lemniscatus (Duméril, Bibron and Duméril, 1854) (Serpentes, Dipsadidae)?

The snake Phalotris lemniscatus is a polymorphic species regarding color, which varies between light shades with a yellow predominance (pale yellow-brown) to darker shades with a red predominance (red-dark). Pale yellow-brown individuals are more frequent in coastal populations while there is a tendency of increasing the frequency of red-dark morphs in inland areas. Considering the variation in substrate color along the species distribution (light/sandy on the coast to reddish and dark/argillaceous in inland areas), we raise the hypothesis that the predation rate of each morph would be lower in sites were its crypsis potential is higher. If correct, this hypothesis would reinforce the idea that the predation risk is one of the factors influencing the spatial structuring in morph frequency distributions in populations of P. lemniscatus . To test this hypothesis, we performed a field experiment using plasticine P. lemniscatus artificial models that represent two morphs: red-dark and pale yellow-brown. The models were distributed in three localities where the following substrate types predominate: light (Coastal Site), intermediary (Lowland Site) and reddish dark (Highland Site). Our predictions were corroborated only at the coastal site, where the less cryptic morph was the most preyed one. We verified that there is a regional variation in the predation risk on different morphs. Thus, the possibility that the selective pressure by predators is a relevant element in the structuring of the frequencies of different morph populations of this species cannot be completely excluded.

Basic principles of anaesthesia of small mammals: part 1

Anaesthesia of small mammals (rabbits, ferrets and rodents) is associated with a higher risk compared with anaesthesia of dogs and cats. Clinical history and pre-anaesthetic assessment are often not as accurate as in cats and dogs, and underlying subclinical pathologies may be unrevealed. Additionally, anatomical and physiological characteristics typical of some of these species may contribute to anaesthesia-related mortality. Rabbits, guinea pigs, hamsters and rats are prey animals, highly susceptible to stress: a quiet environment must be offered during the perioperative period and intramuscular premedication can help reducing stress related to intravenous cannulation and induction of general anaesthesia. Challenging endotracheal intubation and (in herbivores) the high risk of post-operative ileus are important considerations when anaesthetising these species. Finally, monitoring of temperature and of the cardiovascular and respiratory systems must be performed not only intraoperatively but also during the recovery period until the patient is fully awake.

Who’s where? Ecological uncertainty shapes neophobic predator avoidance in Trinidadian guppies

Neophobic predator avoidance (NPA), the fear response exhibited by prey animals exposed to novel stimuli, is a plastic trait thought to be induced by exposure to elevated chronic risk of predation. Indeed, prey experiencing low levels of background risk fail to display NPA, while those experiencing high background risk do display NPA. Recent work has suggested that the trigger for inducing and maintaining NPA may not be background risk per se but rather uncertainty in the predation environment. Here, we designed two experiments on wild-caught neophobic Trinidadian guppies (Poecilia reticulata) to test the ‘uncertainty hypothesis’. In the first experiment, we tested if the diversity of novel stimuli encountered by guppies would affect the maintenance of their NPA. We found that exposure to a single novel odour once per day for 3 days was sufficient to extinguish the neophobic response to that odour (Experiment 1A) but not a new odour (Experiment 1B). However, when guppies were exposed to multiple novel odours so that each odour was encountered once a day for 3 days, they retained their NPA to both a previously encountered novel odour (Experiment 1A) and a new odour (Experiment 1B). In our second experiment, we repeatedly exposed guppies to a novel cue in a spatially predictable vs. unpredictable location and found that spatial unpredictability interfered with the reduction of NPA to that cue. Combined, our results suggest that uncertainty of risk experienced by prey in time and space shapes the retention of NPA. When prey face uncertainty, or lack of complete information, about risk in their environment, they engage in adaptive antipredator behaviours such as neophobic predator avoidance. Showing a fear response to a novel stimulus in a high-risk environment is likely adaptive if we assume that most species in that environment are threats. Here, we aim to show how uncertainty, as opposed to simply background levels of risk, may influence the maintenance of neophobic responses in prey. On the basis of two experiments, we showed that prey experiencing increased uncertainty, via increased diversity and spatial unpredictability of novel cues, maintain their neophobic responses more so than prey experiencing lower uncertainty. Understanding the effects of ecological uncertainty on prey behaviour, particularly neophobia, will shed light on how prey might respond as uncertainty increases with climate change, invasive species and anthropogenic habitat modification.

Predating activity and prey impact on life cycle and development of predatory mite (amblysieus swirskii)

Amblyseius swirskii is commonly used to control whitefly and thrips, twospotted spider mite(T.urticae) in greenhouse vegetables and some ornamental crops. This study in each of three different types(two spotted spider mite feeding , pollen feeding, thrips feeding) of feeding pray, 1 females were observed to die at relative humidity 35-60% and at temperatures of 25-300С, laboratory light:dark(16:8) and characteristics of the pray were studied in the development of fertility. We studied mite’s nutritional features, and hunting activities. Amblysieus swirskii’s egg development good establish 2.18±0.17 days in environment which is pollen feeding, 2.48±0.04 days in thrips feeding environment, 2.014±0.098 in two spotted spider mite feeding environment, Growth is until Larvae turned to Nymph there is a hole day in three environments, until Nymph turned to adult tick there are 3.13±0.23 days in pollen feeding environment, 3.25±0.29 days in thrips feeding environment, 2.014±0.098 two spotted spider mite prey environment. A Generation 6.3±0.3 day’s pollen feeding environment, 6.72±0.25 days in thrips feeding environment, 6.55±0.32 days in two spotted spider mite prey environment. Therefore conclusion is feeding environment doesn’t influence their life cycle. Research shows that adult antelope feeds with 15.2 two spotted spider mite, 5.1 thrips daily, decreasing it`s population. Having observed the females egg development in three different types of feeding environment it showed highest result, 14 days, at a temperature of 29.7 1.47C and 30 3.33% moisture environment. In contrast it showed its lowest result, 6 days, in dusty feeding environment whereas in environment with thrips it lay it`s eggs in 12 days for an average. Observing Amblysieus swirskii’s laying egg and lifespan, found out that they able to lay 13±2.6 eggs in two spotted spider mite provision environment, 13.6±2.08 days survive. In thrips feeding environment laying 6.3±0.5 eggs and survive 12.3±2.08 days, in pollen feeding environment laying 4±1 eggs, 7.6±0.5 days surviving.
 Ангуучин амблисейус (аmblysieus swirskii) хачгийн идэш тэжээлийн онцлог, үржил хөгжил, ангуучлах идэвхийг судалсан дүн
 Хураангуй: Ангуучин хачиг амблисейус (Аmblysieus swirskii)ийн үржил хөгжлийг лабораторийн гэрэл: харанхуй (16:8), 25-300С дулаантай, 35-60% чийгшилтэй орчинд ургамлын тоос, шүлхий хачиг, трипс гэсэн гурван идэш тэжээлийн хувилбартайгаар үржил хөгжил, ангуучлах идэвхийг судлав.Ангуучин хачиг амблисейус (Аmblysieus swirskii)-ийн өндөгний хөгжил ургамлын тоос идэштэй орчинд 2.18±0.17 хоног, трипс идэштэй орчинд 2.48±0.04 хоног, шүлхий хачиг идэштэй орчинд 2.014±0.098 хоног авгалдайнаас нимф болох шатанд гурван орчинд бүгд 1 хоног, нимфээс бие гүйцсэн ангуучин хачиг болох шатанд тоос идэштэй орчинд 3.13±0.23 хоног, трипс идэштэй орчинд 3.25±0.29 хоног, энгийн шүлхий хачиг идэштэй орчинд 2.014±0.098 хоног тус тус бойжсон бол 1 үе удам нь тоосоор хооллосон орчинд 6.3±0.3 хоног, трипсээр хооллосон орчинд 6.72±0.25 хоног, энгийн шүлхий хачгаар хооллосон орчинд 6.55±0.32 хоног тус тус үргэлжлэв. Ангуучин бие гүйцсэн амблисейус (Аmblysieus swirskii) хачгийн ангуучлах идэвхийг судлахад өдөрт 15.2 шүлхий хачиг, 5.1 трипс дунджаар идэж тоо, толгойг бууруулж байна. Эмэгчин хачгийн төлөрхөг чанарыг дээр дурьдсан гурван идэш тэжээлийн орчинд судлахад шүлхий хачиг идэш тэжээлийн орчинд хамгийн олон хоног өндөглөсөн буюу дунджаар 14 хоног, хамгийн цөөн хоног өндөглөсөн буюу тоостой идэш тэжээлийн орчинд дунджаар 6 хоног өндөглөсөн бол трипстэй идэш тэжээлийн орчинд дунджаар 12 хоногийн турш өндөглөлт үргэжилж байна. Ангуучин хачгийн өндөглөлт ба амьдрах хугацааг тогтооход энгийн шүлхий хачиг идэш тэжээлийн орчинд 13±2.6 өндөг төрүүлж, 13.6±2.08 хоног амьдарч, трипс идэш тэжээлийн орчинд 6.3±0.5 өндөг гаргаж 12.3±2.08 хоног амьдаржилж басан бол тоостой идэш тэжээлийн орчинд 4±1 өндөг гаргаж 7.6±0.5 хоног тус тус амьдарч байгааг тогтоов.
 Түлхүүр үг: Биологийн хамгаалал, ангуучлах идэвх, идэш тэжээлийн онцлог

Spiny but Subitaneous Eggs: Egg Morphology and Hatching in Acartia Copepods in the Tropics.

Egg surface ornamentation, egg production rates, and hatching success of two calanoid copepod species (Acartia pacifica and Acartia cf. erythraea) were examined in a tropical coral reef of Tioman Island, Malaysia, near the equator (2°N). All observed females of A. pacifica and A. cf. erythraea produced eggs with spines on the surface, either short or long, which are common in resting eggs in temperate ecosystems that hatch when environmental conditions are favorable or after a certain refractory period. However, all of these spiny eggs in the present study hatched within 48 hours when exposed to ambient seawater temperature, suggesting that they were subitaneous eggs. Such spine ornamentation has been thought to be an adaptive feature only for resting eggs to survive during egg dormancy, but the presence of spines on subitaneous eggs suggests further possible functions of these spines such as reducing the risks of ingestion by predators.

Beasts of Prey or Rational Animals? Private Governance in Brazil’s Jogo do Bicho

A rational-choice account of Brazil’s jogo do bicho (animal game), possibly the largest illegal lottery game in the world, examines the mechanisms that have fostered the lottery’s notable growth outside the boundaries of Brazilian law and reveals how animal-game financiers combine costly signals and selective incentives to induce cooperation from members of the community and exploit the fragmentation of Brazil’s political system to advance their long-term interests. Uma abordagem da teoria da escolha racional do jogo do bicho, possivelmente o maior jogo de loteria ilegal do mundo, examina os mecanismos que fomentaram o crescimento notável da loteria fora dos limites da lei brasileira e revela como os financiadores de jogos de animais combinam caros sinais e incentivos seletivos para induzir a cooperação de membros da comunidade e explorar a fragmentação do sistema político brasileiro para promover seus interesses de longo prazo.

Selective consumption of sacoglossan sea slugs (Mollusca: Gastropoda) by scleractinian corals (Cnidaria: Anthozoa).

Recent studies revealed that reef corals can eat large-sized pelagic and benthic animals in addition to small planktonic prey. As follow-up, we document natural ingestion of sea slugs by corals and investigate the role of sacoglossan sea slugs as possible prey items of scleractinian corals. Feeding trials were carried out using six sacoglossan species as prey, two each from the genera Costasiella, Elysia and Plakobranchus, and four free-living solitary corals (Danafungia scruposa, Fungia fungites, Pleuractis paumotensis and Heteropsammia cochlea) as predators. Trials were carried out under both in-situ and ex-situ conditions with the aim to observe ingestion and assess signs of prey consumption based on tissue loss of prey individuals over time. Significant differences were observed in both ingestion time and consumption state of prey between prey species, with three of them being ingested more rapidly and preferentially consumed over the others. Additionally, prey size was found to be a significant factor with larger prey (>12 mm) being ingested more slowly and rarely than smaller ones (<6 mm and 6–12 mm). Comparisons of consumption capability among predators showed no significant difference with all coral species showing similar preferences for prey species. While no specific mechanism of prey capture is proposed, we also document instances of kleptoparisitism and resuspension of prey items by wrasses. This study highlights the important distinction between opportunistic prey capture and true predation events.

Conflict in the air

Conservation The heather-coated uplands of the British Isles are home to two charismatic and specialized birds: the commercially valuable red grouse and its rare raptor predator, the hen harrier. These species are the focus of an often-emotional conflict after highly publicized poisonings of hen harriers. St John et al. analyzed the basis of the human confrontation and report on the results of a questionnaire answered by more than 500 members of field sport and nature conservation organizations. There was an apparently irreconcilable gulf in responses to management approaches, depending on whether the respondent was pro–grouse conservation for hunting or pro–bird conservation overall. The authors concluded that there may be some prospects for consensus if the adversaries are engaged in joint planning for the longer-term future of the British upland landscape. People Nat. 1 , 6 (2019).

Study on predatory mites of Aceria tristriatus (Nalepa, 1890) from Hamedan and Lorestan provinces, Western Iran

The walnut leaf gall mite ( Aceria tristriatus ) is one of the major pests of walnut in western Iran. Therefore, a study to determine the predatory mites associated with this pest in Hamedan and Lorestan provinces was carried out during 2014–2017. In this survey, totally 10 species belong to six genera and three different families including Phytoseiidae: Kuzinellus kuzini Wainstein, Typhlodromus bagdasarjani Wainstein & Arutunjan, Typhlodromus khosrovensis Arutunjan, Euseius finlandicus Oudemans; Iolinidae: Neopronematus iranensis Ahmad-Hosseini et al. , Neopronematus solani Ripka et al. , Pronematus rykei Meyer & Rodrigues; Tydeidae: Tydeus caryae Khanjani & Ueckermann, Tydeus goetzi Schruft, and Tydeus electus Kuznetzov were collected and identified. Kuzinellus kuzini Wainstein had the highest frequency and distribution in this survey. Among the collected species, Typhlodromus khosrovensis , Typhlodromus bagdasarjani , E. finlandicus , N. solani , Tydeus caryae , Tydeus goetzi and Tydeus electus are re-described in the present paper. Tydeus goetzi and Neopronematus solani are reported for the first time for Hamedan and Lorestan provinces.

A cross-modality enhancement of defensive flight via parvalbumin neurons in zona incerta.

The ability to adjust defensive behavior is critical for animal survival in dynamic environments. However, neural circuits underlying the modulation of innate defensive behavior remain not well-understood. In particular, environmental threats are commonly associated with cues of multiple sensory modalities. It remains to be investigated how these modalities interact to shape defensive behavior. In this study, we report that auditory-induced defensive flight behavior can be facilitated by somatosensory input in mice. This cross-modality modulation of defensive behavior is mediated by the projection from the primary somatosensory cortex (SSp) to the ventral sector of zona incerta (ZIv). Parvalbumin (PV)-positive neurons in ZIv, receiving direct input from SSp, mediate the enhancement of the flight behavior via their projections to the medial posterior complex of thalamus (POm). Thus, defensive flight can be enhanced in a somatosensory context-dependent manner via recruiting PV neurons in ZIv, which may be important for increasing survival of prey animals.

Adaptation by way of compromise

Evolutionary Biology Many plants rely on animal pollinators to spread pollen and increase the genetic diversity of their offspring. However, there are trade-offs, because attracting pollinators may also attract herbivores and deterring predation may diminish floral displays. Ramos and Schiestl studied the interplay between mating system, flowers, and chemical defenses over several generations in Brassica rapa plants (see the Perspective by Agren). Evolution driven by pollination and herbivory can be observed after only eight generations, suggesting that trade-offs have large evolutionary consequences. Science , this issue p. [193][1]; see also p. [122][2] [1]: /lookup/doi/10.1126/science.aav6962 [2]: /lookup/doi/10.1126/science.aax1656

Ecosystems feel war's effects

Trophic Cascades War ravages human lives and landscapes, but nonhuman victims are no less affected. The Mozambican Civil War resulted in the rapid decline of predators in Gorongosa National Park and led to a trophic cascade that shifted prey behaviors and plant communities. Atkins et al. monitored this shift and found that the absence of wild dogs and leopards resulted in a change in habitat use and plant consumption by bushbuck, which are forest-dwelling antelopes. Experiments further showed that changes in prey behavior were reversible when signs of predator activity were introduced, supporting the impact of the predator loss. These results confirm patterns seen elsewhere and go further in providing mechanistic detail about the importance of the “landscape of fear” perceived by prey animals. Science , this issue p. [173][1] [1]: /lookup/doi/10.1126/science.aau3561

Kamuflase dan Strategi Antipredasi Pada Kepiting Hantu Ocypode (Weber, 1795) di Pantai Congot, Kulonprogo, Yogyakarta

Antipredation adalah salah satu jenis adaptasi yang dilakukan oleh hewan mangsa dalam menghadapi predator, baik yang menghindar maupun bertarung. Strategi antipredasi yang paling sering dilakukan oleh beberapa hewan adalah dengan menipu para predator, salah satunya dengan kamuflase. Dalam kepiting hantu yang disamarkan dilakukan dengan menggunakan teknik pencocokan latar belakang, yang mengubah warna tubuh mereka dan mencocokkannya dengan warna lingkungan mereka dengan menyesuaikan konsentrasi dan dispersi pigmen di chromatophore (Davies, 2013). Selain kamuflase, kepiting hantu juga menjadikan lubang sebagai tempat persembunyian pemangsa. Dengan mengacu pada strategi kamuflase dan antipredasi pada Kepiting Hantu (Ocypode), perlu dilakukan penelitian yang meneliti perilaku strategi antipredasi yang mencakup kamuflase dan arsitektur liang kepiting hantu di Pantai Congot, Kulonprogo, Yogyakarta. Metode yang digunakan dalam penelitian ini termasuk mengambil data potret cahaya tampak menggunakan Ocypode dan lingkungannya untuk menganalisis nilai RGB, kemudian membandingkan komposisi RGB dengan spesimen dan lingkungannya dengan indeks Euclidean Distance. Selain itu, pengumpulan data arsitektur liang menggunakan bubuk gypsum disterilkan dengan air dan kemudian dibiarkan kering dan kemudian hasil cetakan diukur dan dianalisis. Hasil yang diperoleh antara lain nilai Euclidian Distance sebesar 0,12 yang menunjukkan bahwa warna pada karapas sesuai dengan warna lingkungan. Selain itu, ada 29 cor arsitektur liang yang terdiri dari 20 bentuk-I, 2 bentuk-J, 2 bentuk-L, 1 bentuk spiral 3-Y, dan 1 bentuk kompleks.

Anxiety and depression like behaviors in chronic Parkinsonism of cynomolgus monkey

Objective To establish and evaluate anxiety and depression like behaviors in MPTP-induced chronic Parkinsonism cynomolgus monkey. Methods Ten cynomolgus monkeys (15.0±1.5 years old) were divided into normal group and MPTP-induced parkinsonism group(PD group), 5 animals in each group.The behavioral methods for evaluating the anxiety and depression like behaviors in non-human primates included Apathy Feeding Test (AFT), Human Intruder Test (HIT), Novel Fruit Test (NFT) and Predator Confrontation Test (PCT). The changes in behavioral indicators between the two groups were analyzed. Results In AFT, PD group spent more time in observing food on both sides, and significantly higher than that in normal group (left: 0.73(0.49)s, 0.50(0.28)s, P 0.05), while normal group spent more time in the back of cage during Stare and Back period( Stare: 0(64.70)s, 111.27(38.94)s, P=0.033; Back: 0(25.84)s, 120(114.69)s; H=17.397). Finally, PD group had lower take-up rate and higher withdrawal rate than normal group in PCT(P>0.05). Conclusion This study establishes a multi-angle evaluation of behavioral methods for anxiety and depression in non-human primates.The analysis confirmed that chronic Parkinson's disease cynomolgus monkeys has different degrees of anxiety and depression, which provides a new method for preclinical intervention in Parkinson's disease. Key words: Parkinson's disease; Cynomolgus monkey; Anxiety; Depression; Human intruder test; Apathy feeding test; Novel fruit test; Predator confrontation test

Picky carnivorous plants? Investigating preferences for preys' trophic levels - a stable isotope natural abundance approach with two terrestrial and two aquatic Lentibulariaceae tested in Central Europe.

Stable isotope two-source linear mixing models are frequently used to calculate the nutrient-uptake efficiency of carnivorous plants from pooled prey. This study aimed to separate prey into three trophic levels as pooled prey limits statements about the contribution of a specific trophic level to the nutrition of carnivorous plants. Phytoplankton were used as an autotrophic reference for aquatic plants as the lack of suitable reference plants impedes calculation of their efficiency. Terrestrial (Pinguicula) and aquatic (Utricularia) carnivorous plants alongside autotrophic reference plants and potential prey from six sites in Germany and Austria were analysed for their stable isotope natural abundances (δ15N, δ13C). A two-source linear mixing model was applied to calculate the nutrient-uptake efficiency of carnivorous plants from pooled prey. Prey preferences were determined using a Bayesian inference isotope mixing model. Phytophagous prey represented the main contribution to the nutrition of Pinguicula (approx. 55 %), while higher trophic levels contributed a smaller amount (diverse approx. 27 %, zoophagous approx. 17 %). As well as around 48 % nitrogen, a small proportion of carbon (approx. 9 %) from prey was recovered in the tissue of plants. Aquatic Utricularia australis received 29 % and U. minor 21 % nitrogen from zooplankton when applying phytoplankton as the autotrophic reference. The separation of prey animals into trophic levels revealed a major nutritional contribution of lower trophic level prey (phytophagous) for temperate Pinguicula species. Naturally, prey of higher trophic levels (diverse, zoophagous) are rarer, resulting in a smaller chance of being captured. Phytoplankton represents an adequate autotrophic reference for aquatic systems to estimate the contribution of zooplankton-derived nitrogen to the tissue of carnivorous plants. The autonomous firing of Utricularia bladders results in the additional capture of phytoplankton, calling for new aquatic references to determine the nutritional importance of phytoplankton for aquatic carnivorous plants.

Author response: Subcutaneous ofatumumab in patients with relapsing-remitting multiple sclerosis: The MIRROR study.

On behalf of all authors, we thank Dr. Kearney for the comment on our article.1 The reported “90% reduction in gadolinium-enhancing lesions,” referred to by Dr. Kearny, should only be considered inflated if our article claimed these results are to be compared to results of active comparator studies such as the alemtuzumab vs interferon study (our study was not an active comparator study).2 With respect to “time is brain,” we fully agree and the same trial design would not be currently pursued. While only published in 2018, the results of the MIRROR study were first presented over 4 years prior, with design and execution that predated that by approximately 2 additional years.

External body temperature and vigilance to a lesser extent track variation in predation risk in domestic fowls

BackgroundThe animal ecology literature proposes the view that predation risk induces fear in prey animals, but it is also possible that behavioral and physiological changes induced by predation risk are not associated with fear at all. If we view fear as a state indicated by measurable changes in behavior and physiology caused by threats, then it is valid to search for a link between markers of fearfulness and predation risk. I predicted that domestic fowls (Gallus gallus domesticus) foraging alone, and thus exposed to higher predation risk, would show higher vigilance (a behavioral marker of fearfulness) and lower external body temperature (a physiological marker of fearfulness) than domestic fowls foraging in pairs. These adjustments should become less prominent in the continued absence of threats during a trial.ResultsDomestic fowls that foraged alone rather than in pairs showed higher vigilance and lower external body temperature. While external body temperature returned to baseline values during a trial, vigilance unexpectedly increased. The results thus provide mixed support for an association between markers of fearfulness and predation risk.ConclusionsI argue that vigilance is not always a sensitive marker of fearfulness because hunger can keep vigilance low even in risky settings. By contrast, external body temperature varied with group size and time during a trial, suggesting that this marker is more sensitive. Future studies are needed to validate the relationship between markers of fearfulness and predation risk.

Infrared-sensing snakes select ambush orientation based on thermal backgrounds

Sensory information drives the ecology and behaviour of animals, and some animals are able to detect environmental cues unavailable to us. For example, rattlesnakes use infrared (IR) radiation to detect warm prey at night when visual cues are reduced. Until recently these sensory worlds have been inaccessible to human observers; now technology can allow us to “eavesdrop” on these species and understand how sensory perception drives ecology and behaviour. We used thermography and computer simulations to examine how prey-background temperature contrast and areas of temperature transitions influence the angular orientation of free-ranging rattlesnakes once they have selected an ambush site. We tracked free-ranging sidewinder rattlesnakes Crotalus cerastes to their selected ambush sites and recorded 360° near-ground thermographic panoramas from the centre of the ambush site. A computer simulation then moved a simulated prey item across the panorama and computed a contrast index for all directions. Rattlesnakes did not face ambush directions that offered stronger contrast than average, but they demonstrated a striking tendency to face directions with strong thermal transitions. Background transitions likely create a readily detected, rapidly changing stimulus when a prey animal passes. Quantifications of sensory environments like this one can boost our comprehension of how sensory function impacts the ecology, behaviour, and evolution of animals.

Risk allocation: acute and chronic predator exposure have contrasting effects on Song Sparrow (Melospiza melodia) singing behaviour

Increasing the danger posed by predators may cause prey animals to alter their behaviour. For example, they may be more vigilant and so feed more slowly. Breeding male Song Sparrows (Melospiza melodia (A. Wilson, 1810)) spend much time in conspicuous, loud song, which is an important behaviour for territorial defense and for mate attraction. We measured their singing behaviour in relation to both chronic (active Cooper’s Hawk (Accipiter cooperii (Bonaparte, 1828)) nest nearby) and acute (playback of hawk calls) predator exposure. We found that proximity to a Cooper’s Hawk nest had little or no influence. In contrast, the response to acute exposure was strong and immediate: Song Sparrows reduced the song rate and the proportion of time spent singing, lowered perch height, and increased concealment. The decline in the amount of song during the few minutes following playback attributable to the acute exposure was 34.6%. We analyze these results in light of theories about how animals adjust risk taking in response to predation danger. Given that the numbers of their predators have risen steadily for the past few decades and affect the level of singing, we consider the implications for trend estimates of songbird populations based on surveys using auditory methods.