Sector search strategies for odor trail tracking

Ants, mice, and dogs often use surface-bound scent trails to establish navigation routes or to find food and mates, yet their tracking strategies remain poorly understood. Chemotaxis-based strategies cannot explain casting, a characteristic sequence of wide oscillations with increasing amplitude performed upon sustained loss of contact with the trail. We propose that tracking animals have an intrinsic, geometric notion of continuity, allowing them to exploit past contacts with the trail to form an estimate of where it is headed. This estimate and its uncertainty form an angular sector, and the emergent search patterns resemble a “sector search.” Reinforcement learning agents trained to execute a sector search recapitulate the various phases of experimentally observed tracking behavior. We use ideas from polymer physics to formulate a statistical description of trails and show that search geometry imposes basic limits on how quickly animals can track trails. By formulating trail tracking as a Bellman-type sequential optimization problem, we quantify the geometric elements of optimal sector search strategy, effectively explaining why and when casting is necessary. We propose a set of experiments to infer how tracking animals acquire, integrate, and respond to past information on the tracked trail. More generally, we define navigational strategies relevant for animals and biomimetic robots and formulate trail tracking as a behavioral paradigm for learning, memory, and planning.

Evaluating Environmental Enrichment Methods in Three Zoo-Housed Varanidae Lizard Species

Environmental enrichment has been shown to enhance the behavioural repertoire and reduce the occurrence of abnormal behaviours, particularly in zoo-housed mammals. However, evidence of its effectiveness in reptiles is lacking. Previously, it was believed that reptiles lacked the cognitive sophistication to benefit from enrichment provision, but studies have demonstrated instances of improved longevity, physical condition and problem-solving behaviour as a result of enhancing husbandry routines. In this study, we evaluate the effectiveness of food- and scent-based enrichment for three varanid species (Komodo dragon, emerald tree monitor lizard and crocodile monitor). Scent piles, scent trails and hanging feeders resulted in a significant increase in exploratory behaviour, with engagement diminishing ≤330 min post provision. The provision of food- versus scent-based enrichment did not result in differences in enrichment engagement across the three species, suggesting that scent is just as effective in increasing natural behaviours. Enhancing the environment in which zoo animals reside is important for their health and wellbeing and also provides visitors with the opportunity to observe naturalistic behaviours. For little known and understudied species such as varanids, evidence of successful (and even unsuccessful) husbandry and management practice is vital for advancing best practice in the zoo industry.

The Triggering Track-Ways Theory

<p>In this thesis I present a new paradigm in human evolutionary theory: the relevance of track-ways reading (TWR) to the evolution of human cognition, culture and communication. Evidence is presented that strongly indicates hominins were exploiting conspecific track-ways 4 million years ago. For a non-olfactory ape that was a specialized forager in open, featureless wetland environments, they were the only viable natural signs to exploit for safety, orienteering, and recognizable social markers. Due to the unique cognitive demands of reading track-ways, as compared to scent-trails all other animals use to find each other and preferred prey species, social TWR triggered the evolution of a unique faculty for narrative elsewhere-and-when cognition in the hominin mind. Two million years later, this narrative faculty was entrenched enough to enable the rather sudden "explosion" of co-operative Oldowan Lithic Culture that began at 2.6mya. This cultural adaptation was a highly successful response to catastrophic environmental change. Thereafter selection for encephalization to increase neural capacity to store and co-operatively exploit socio-ecological knowledge gained from the hominin narrative faculty (via co-evolving, increasingly efficient modes of intentional communication) drove all further biological and cultural developments in the hominin trajectory towards H.sapiens and behavioural modernity.</p>

The Triggering Track-Ways Theory

<p>In this thesis I present a new paradigm in human evolutionary theory: the relevance of track-ways reading (TWR) to the evolution of human cognition, culture and communication. Evidence is presented that strongly indicates hominins were exploiting conspecific track-ways 4 million years ago. For a non-olfactory ape that was a specialized forager in open, featureless wetland environments, they were the only viable natural signs to exploit for safety, orienteering, and recognizable social markers. Due to the unique cognitive demands of reading track-ways, as compared to scent-trails all other animals use to find each other and preferred prey species, social TWR triggered the evolution of a unique faculty for narrative elsewhere-and-when cognition in the hominin mind. Two million years later, this narrative faculty was entrenched enough to enable the rather sudden "explosion" of co-operative Oldowan Lithic Culture that began at 2.6mya. This cultural adaptation was a highly successful response to catastrophic environmental change. Thereafter selection for encephalization to increase neural capacity to store and co-operatively exploit socio-ecological knowledge gained from the hominin narrative faculty (via co-evolving, increasingly efficient modes of intentional communication) drove all further biological and cultural developments in the hominin trajectory towards H.sapiens and behavioural modernity.</p>

Foraging and scavenging behaviour of the prairie rattlesnake (Crotalus viridis): no evidence that envenomation cues facilitate kleptoparasitism of struck prey

Most viperids are ambush predators that primarily use venom to subdue prey, employing a strike-release-trail hunting strategy whereby snakes follow the unique scent of envenomated prey to locate carcasses they have bitten and released. In addition to killing prey, rattlesnakes (like most carnivores) will also opportunistically scavenge carrion. This scavenging strategy likely includes the occasional consumption of carcasses killed by other snakes (i.e., kleptoparasitism). In areas with high densities of other pitvipers, utilizing the unique scent of animals envenomated by other snakes might be a viable alternative foraging strategy. We evaluated this possibility experimentally using a series of captive behavioural trials on prairie rattlesnakes (Crotalus viridis) to determine whether conspecific or heterospecific (C. scutulatus, C. ornatus) envenomation cues might increase the likelihood of kleptoparasitism. Rattlesnakes did not prefer envenomated prey over nonenvenomated prey, nor did they prefer venom cues of one species over another. Although they did frequently scavenge carcasses, in the absence of striking, snakes generally located carcasses using random searching movements instead of scent trails. Additionally, the amount of time rattlesnakes spent investigating carcass trails did not differ significantly among treatments, suggesting that striking, and the resultant formation of a chemical search image of prey, is more crucial to trailing behaviour than venom cues. Moreover, a high degree of behavioural variation among individuals was observed, suggesting that scavenging and kleptoparasitism in rattlesnakes is more complex than previously realized, and making generalizations about these behaviours is challenging.

Sector search strategies for odor trail tracking

Terrestrial animals such as ants, mice and dogs often use surface-bound scent trails to establish navigation routes or to find food and mates, yet their tracking strategies are poorly understood. Tracking behavior features zig-zagging paths with animals often staying in close contact with the trail. Upon sustained loss of contact, animals execute a characteristic sequence of sweeping “casts” – wide oscillations with increasing amplitude. Here, we provide a unified description of trail-tracking behavior by introducing an optimization framework where animals search in the angular sector defined by their estimate of the trail’s heading and its uncertainty.In silicoexperiments using reinforcement learning based on this hypothesis recapitulate experimentally observed tracking patterns. We show that search geometry imposes limits on the tracking speed, and quantify its dependence on trail statistics and memory of past contacts. By formulating trail-tracking as a Bellman-type sequential optimization problem, we quantify the basic geometric elements of optimal sector search strategy, effectively explaining why and when casting is necessary. We propose a set of experiments to infer how tracking animals acquire, integrate and respond to past information on the tracked trail. More generally, we define navigational strategies relevant for animals and bio-mimetic robots, and formulate trail-tracking as a novel behavioral paradigm for learning, memory and planning.

A persistent abnormal repetitive behaviour in a false water cobra (Hydrodynastes gigas)

Stereotypies (a subset of Abnormal Repetitive Behaviour [ARB]) are characterised by an unchanging pattern of behaviour and in captive animals can be associated with poor welfare. Although well known in certain taxa, little is known about both welfare and ARBs in reptiles, especially snakes. We document an instance of an ARB in a captive snake species (Hydrodynastes gigas), set it in the context of husbandry in zoos, and assess efforts to reduce it. The stereotypy consisted of a fixed pattern of movement against the enclosures viewing window. Ethographic data were used to focally sample the animals behaviour over several months in the context of different enrichment interventions. Modified Spread of Participation Indices (mSPIs) were also calculated to quantify the evenness of enclosure use. The snake spent considerable portions of time (47 of observations) performing a behaviour that fulfils the criteria for stereotypy. mSPI data suggested a possible welfare impact of the behaviour on the snake. Zoos holding this species globally were surveyed about observations of similar behaviour and one other institution reported similar behaviour. Standard husbandry practice (A) was used alternately in an ABAC format with prey scent trails (B) and modified feeding schedules (C), representing enrichment types based on species natural history. Neither stereotyping frequency nor mSPI was found to be significantly affected by any of the enrichments. Our results, interpretation of which is limited by the paucity of data on snakes, uncover stereotypies in snakes and suggest that, as with other taxa, ARBs may be resistant to strategies employed to reduce them.

The evolution of the urinary bladder as a storage organ: scent trails and selective pressure of the first land animals in a computational simulation

The function of waste control in all living organisms is one of the vital importance. Almost universally, terrestrial tetrapods have a urinary bladder with a storage function. It is well documented that many marine and aerial species do not have an organ of such a function, or have one with very depressed storage functionality. Bladder morphology indicates it has evolved from a thin-walled structure used for osmoregulatory purposes, as it is currently used in many marine animals. It is hypothesised that the storage function of the urinary bladder allows for an evolutionary selective advantage in reducing the likelihood of successful predation. Random walks simulating predator and prey movements with simplified scent trails were utilised to represent various stages of the hunt: Detection and pursuit. A final evolutionary model is proposed in order to display the advantages over inter-generational time scales and illustrates how a bladder may evolve from an osmoregulatory organ to one of the storage. Data sets were generated for each case and analysed indicating the viability of such advantages. From the highly consistent results, three distinct characteristics of having a storage function in the urinary bladder are suggested: reduced scent trail detection rate; increased prey–predator separation (upon scent trail detection); and a reduced probability of successful capture upon scent detection by the predator. Furthered by the evolutionary model indicating such characteristics are conserved and augmented over many generations, it is concluded that prey–predator interactions provide a large selective pressure in the evolution of the urinary bladder and its storage function.

A test of scent-trailing as a contributing factor in the climbing behaviour of the redback salamander (Plethodon cinereus)

Terrestrial salamanders of the family Plethodontidae are common predators of invertebrates in deciduous forest communities of eastern North America. While normally residing and foraging in forest-floor microhabitats, many species facultatively climb vegetation. Different hypotheses have been proffered to explain this behaviour including optimal-foraging strategies and predator avoidance. Using laboratory-based trials, we tested the hypothesis that the terrestrial salamander Plethodon cinereus climbs in response to scent trails left by insect prey. We found that salamanders climbed significantly higher and spent significantly more time climbing on wooden dowel rods that had been treated with prey residue than they did on control rods. Scent trailing possibly interacts with other factors such as optimal-foraging opportunities and predation risk in influencing climbing behaviour in these salamanders.