Climate change drives migratory range shift via individual plasticity in shearwaters.

How individual animals respond to climate change is key to whether populations will persist or go extinct. Yet, few studies investigate how changes in individual behavior underpin these population-level phenomena. Shifts in the distributions of migratory animals can occur through adaptation in migratory behaviors, but there is little understanding of how selection and plasticity contribute to population range shift. Here, we use long-term geolocator tracking of Balearic shearwaters (Puffinus mauretanicus) to investigate how year-to-year changes in individual birds' migrations underpin a range shift in the post-breeding migration. We demonstrate a northward shift in the post-breeding range and show that this is brought about by individual plasticity in migratory destination, with individuals migrating further north in response to changes in sea-surface temperature. Furthermore, we find that when individuals migrate further, they return faster, perhaps minimizing delays in return to the breeding area. Birds apparently judge the increased distance that they will need to migrate via memory of the migration route, suggesting that spatial cognitive mechanisms may contribute to this plasticity and the resulting range shift. Our study exemplifies the role that individual behavior plays in populations' responses to environmental change and highlights some of the behavioral mechanisms that might be key to understanding and predicting species persistence in response to climate change.

How might magnetic secular variation impact avian philopatry?

A tendency to return to the natal/breeding site, 'philopatry', is widespread amongst migratory birds. It has been suggested that a magnetic 'map' could underpin such movements, though it is unclear how a magnetic map might be impacted by gradual drift in the Earth's magnetic field ('secular variation'). Here, using the International Geomagnetic Reference Field, we quantified how secular variation translates to movement in the implied positions at which combinations of different magnetic cues (inclination, declination and intensity) intersect, noting that the magnitude of such movements is determined by the magnitude of the movements of each of the two isolines, and the angle between their movement vectors. We propose that magnetic parameters varying in a near-parallel arrangement are unlikely to be used as a bi-coordinate map during philopatry, but that birds could use near-orthogonal magnetic gradient cues as a bi-coordinate map if augmented with navigation using more local cues. We further suggest that uni-coordinate magnetic information could also provide a philopatry mechanism that is substantially less impacted by secular variation than a bi-coordinate 'map'. We propose that between-year shifts in the position of magnetic coordinates might provide a priori predictions for changes in the breeding sites of migratory birds.

Shearwaters sometimes take long homing detours when denied natural outward journey information.

The cognitive processes (learning and processing of information) underpinning the long-distance navigation of birds are poorly understood. Here, we used the homing motivation of the Manx shearwater to investigate navigational decision making in a wild bird by displacing them 294 km to the far side of a large island (the island of Ireland). Since shearwaters are reluctant to fly over land, the island blocked the direct route home, forcing a navigational decision. Further still, on the far side of the obstacle, we chose a release site where the use of local knowledge could facilitate a 20% improvement in route efficiency if shearwaters were able to anticipate and avoid a large inlet giving the appearance of open water in the home direction. We found that no shearwater took the most efficient initial route home, but instead oriented in the home direction (even once the obstacle became visible). Upon reaching the obstacle, four shearwaters subsequently circumnavigated the land mass via the long route, travelling a further 900 km as a result. Hence, despite readily orienting homewards immediately after displacement, shearwaters seem unaware of the scale of the obstacle formed by a large land mass despite this being a prominent feature of their regular foraging environment.

Shearwaters know the direction and distance home but fail to encode intervening obstacles after free-ranging foraging trips.

While displacement experiments have been powerful for determining the sensory basis of homing navigation in birds, they have left unresolved important cognitive aspects of navigation such as what birds know about their location relative to home and the anticipated route. Here, we analyze the free-ranging Global Positioning System (GPS) tracks of a large sample (n = 707) of Manx shearwater, Puffinus puffinus, foraging trips to investigate, from a cognitive perspective, what a wild, pelagic seabird knows as it begins to home naturally. By exploiting a kind of natural experimental contrast (journeys with or without intervening obstacles) we first show that, at the start of homing, sometimes hundreds of kilometers from the colony, shearwaters are well oriented in the homeward direction, but often fail to encode intervening barriers over which they will not fly (islands or peninsulas), constrained to flying farther as a result. Second, shearwaters time their homing journeys, leaving earlier in the day when they have farther to go, and this ability to judge distance home also apparently ignores intervening obstacles. Thus, at the start of homing, shearwaters appear to be making navigational decisions using both geographic direction and distance to the goal. Since we find no decrease in orientation accuracy with trip length, duration, or tortuosity, path integration mechanisms cannot account for these findings. Instead, our results imply that a navigational mechanism used to direct natural large-scale movements in wild pelagic seabirds has map-like properties and is probably based on large-scale gradients.

Gadfly petrels use knowledge of the windscape, not memorized foraging patches, to optimize foraging trips on ocean-wide scales.

Seabirds must often travel vast distances to exploit heterogeneously distributed oceanic resources, but how routes and destinations of foraging trips are optimized remains poorly understood. Among the seabirds, gadfly petrels (Pterodroma spp.) are supremely adapted for making efficient use of wind energy in dynamic soaring flight. We used GPS tracking data to investigate the role of wind in the flight behaviour and foraging strategy of the Desertas petrel, Pterodroma deserta. We found that rather than visiting foraging hotspots, Desertas petrels maximize prey encounter by covering some of the longest distances known in any animal in a single foraging trip (up to 12 000 km) over deep, pelagic waters. Petrels flew with consistent crosswind (relative wind angle 60°), close to that which maximizes their groundspeed. By combining state-space modelling with a series of comparisons to simulated foraging trips (reshuffled-random, rotated, time-shifted, reversed), we show that this resulted in trajectories that were close to the fastest possible, given the location and time. This wind use is thus consistent both with birds using current winds to fine-tune their routes and, impressively, with an a priori knowledge of predictable regional-scale wind regimes, facilitating efficient flight over great distances before returning to the home colony.

Young frigatebirds learn how to compensate for wind drift.

Compensating for wind drift can improve goalward flight efficiency in animal taxa, especially among those that rely on thermal soaring to travel large distances. Little is known, however, about how animals acquire this ability. The great frigatebird (Fregata minor) exemplifies the challenges of wind drift compensation because it lives a highly pelagic lifestyle, travelling very long distances over the open ocean but without the ability to land on water. Using GPS tracks from fledgling frigatebirds, we followed young frigatebirds from the moment of fledging to investigate whether wind drift compensation was learnt and, if so, what sensory inputs underpinned it. We found that the effect of wind drift reduced significantly with both experience and access to visual landmark cues. Further, we found that the effect of experience on wind drift compensation was more pronounced when birds were out of sight of land. Our results suggest that improvement in wind drift compensation is not solely the product of either physical maturation or general improvements in flight control. Instead, we believe it is likely that they reflect how frigatebirds learn to process sensory information so as to reduce wind drift and maintain a constant course during goalward movement.

Long-term spatiotemporal stability and dynamic changes in helminth infracommunities of spiny mice (Acomys dimidiatus) in St. Katherine's Protectorate, Sinai, Egypt.

The importance of parasites as a selective force in host evolution is a topic of current interest. However, short-term ecological studies of host-parasite systems, on which such studies are usually based, provide only snap-shots of what may be dynamic systems. We report here on four surveys, carried out over a period of 12 years, of helminths of spiny mice (Acomys dimidiatus), the numerically dominant rodents inhabiting dry montane wadis in the Sinai Peninsula. With host age (age-dependent effects on prevalence and abundance were prominent) and sex (female bias in abundance in helminth diversity and in several taxa including Cestoda) taken into consideration, we focus on the relative importance of temporal and spatial effects on helminth infracommunities. We show that site of capture is the major determinant of prevalence and abundance of species (and higher taxa) contributing to helminth community structure, the only exceptions being Streptopharaus spp. and Dentostomella kuntzi. We provide evidence that most (notably the Spiruroidea, Protospirura muricola, Mastophorus muris and Gongylonema aegypti, but with exceptions among the Oxyuroidae, e.g. Syphacia minuta), show elements of temporal-site stability, with a rank order of measures among sites remaining similar over successive surveys. Hence, there are some elements of predictability in these systems.

Carry-over effects on the annual cycle of a migratory seabird: an experimental study.

Long-lived migratory animals must balance the cost of current reproduction with their own condition ahead of a challenging migration and future reproduction. In these species, carry-over effects, which occur when events in one season affect the outcome of the subsequent season, may be particularly exacerbated. However, how carry-over effects influence future breeding outcomes and whether (and how) they also affect behaviour during migration and wintering is unclear. Here we investigate carry-over effects induced by a controlled, bidirectional manipulation of the duration of reproductive effort on the migratory, wintering and subsequent breeding behaviour of a long-lived migratory seabird, the Manx shearwater Puffinus puffinus. By cross-fostering chicks of different age between nests, we successfully prolonged or shortened by ∼25% the chick-rearing period of 42 breeding pairs. We tracked the adults with geolocators over the subsequent year and combined migration route data with at-sea activity budgets obtained from high-resolution saltwater-immersion data. Migratory behaviour was also recorded during non-experimental years (the year before and/or two years after manipulation) for a subset of birds, allowing comparison between experimental and non-experimental years within treatment groups. All birds cared for chicks until normal fledging age, resulting in birds with a longer breeding period delaying their departure on migration; however, birds that finished breeding earlier did not start migrating earlier. Increased reproductive effort resulted in less time spent at the wintering grounds, a reduction in time spent resting daily and a delayed start of breeding with lighter eggs and chicks and lower breeding success the following breeding season. Conversely, reduced reproductive effort resulted in more time resting and less time foraging during the winter, but a similar breeding phenology and success compared with control birds the following year, suggesting that 'positive' carry-over effects may also occur but perhaps have a less long-lasting impact than those incurred from increased reproductive effort. Our results shed light on how carry-over effects can develop and modify an adult animal's behaviour year-round and reveal how a complex interaction between current and future reproductive fitness, individual condition and external constraints can influence life-history decisions.

Dual foraging and pair coordination during chick provisioning by Manx shearwaters: empirical evidence supported by a simple model.

The optimal allocation of time and energy between one's own survival and offspring survival is critical for iteroparous animals, but creates a conflict between what maximises the parent's fitness and what maximises fitness of the offspring. For central-place foragers, provisioning strategies may reflect this allocation, while the distance between central-places and foraging areas may influence the decision. Nevertheless, few studies have explored the link between life history and foraging in the context of resource allocation. Studying foraging behaviour alongside food load rates to chicks provides a useful system for understanding the foraging decisions made during parent-offspring conflict. Using simultaneously deployed GPS and time-depth recorders, we examined the provisioning strategies in free-living Manx shearwaters Puffinus puffinus, which were caring for young. Our results showed a bimodal pattern, where birds alternate short and long trips. Short trips were associated with higher feeding frequency and larger meals than long trips, suggesting that long trips were performed for self-feeding. Furthermore, most foraging was carried out within 100 km of sea fronts. A simple model based on patch quality and travel time shows that for Manx shearwaters combining chick feeding and self-maintenance, bimodal foraging trip durations optimise feeding rates.

Unexpectedly deep diving in an albatross.

Albatrosses are the iconic aerial wanderers of the oceans, supremely adapted for long-distance dynamic soaring flight. Perhaps because of this they are considered poorly adapted for diving1, in contrast to many smaller shearwater and petrel relatives, despite having amphibious eyes2, and an a priori mass advantage for oxygen-storage tolerance3. Modern biologging studies have largely confirmed this view4,5, casting doubt on earlier observations using capillary tube maximum depth gauges1, which may exaggerate depths, and emphasising albatrosses' reliance on near-surface feeding. Nevertheless, uncertainty about albatross diving remains an important knowledge gap since bycatch in human fisheries (e.g. birds becoming hooked when diving for longline bait fish) is thought to be driving many population declines in this most threatened group of birds6. Here we show, using miniature electronic depth loggers (TDRs), that black-browed albatross, Thalassarche melanophris, can dive to much greater depths (19 m) and for much longer (52 s) than previously thought - three times the maxima previously recorded for this species (6 m and 15 s), and more than twice the maxima reliably recorded previously for any albatross (from 113.7 bird-days of tracking4,5,7). Further evidence that diving may be a significant behavioural adaptation in some albatrosses comes from co-deployed 3-axis accelerometers showing that these deeper dives, which occur in most individuals we tracked, involve active under-water propulsion without detectable initial assistance from momentum, sometimes with bottom phases typical of active prey pursuit. Furthermore, we find (from co-deployed GPS) that diving occurs primarily in the distal portions of long-distance foraging trips, with deeper dives occurring exclusively during daylight or civil twilight, confirming the importance of visual guidance.

Magnetic stop signs signal a European songbird's arrival at the breeding site after migration.

Although it is known that birds can return to their breeding grounds with exceptional precision, it has remained a mystery how they know when and where to stop migrating. Using nearly a century's worth of Eurasian reed warbler (Acrocephalus scirpaceus) ringing recoveries, we investigated whether fluctuations in Earth's magnetic field predict variation in the sites to which birds return. Ringing recoveries suggest that magnetic inclination is learned before departure and is subsequently used as a uni-coordinate "stop sign" when relocating the natal or breeding site. However, many locations have the same inclination angle. Data from populations with different migratory directions indicate that birds solve this ambiguity by stopping at the first place where the right inclination is encountered on an inherited return vector.

Optimization of dynamic soaring in a flap-gliding seabird affects its large-scale distribution at sea.

Dynamic soaring harvests energy from a spatiotemporal wind gradient, allowing albatrosses to glide over vast distances. However, its use is challenging to demonstrate empirically and has yet to be confirmed in other seabirds. Here, we investigate how flap-gliding Manx shearwaters optimize their flight for dynamic soaring. We do so by deriving a new metric, the horizontal wind effectiveness, that quantifies how effectively flight harvests energy from a shear layer. We evaluate this metric empirically for fine-scale trajectories reconstructed from bird-borne video data using a simplified flight dynamics model. We find that the birds' undulations are phased with their horizontal turning to optimize energy harvesting. We also assess the opportunity for energy harvesting in long-range, GPS-logged foraging trajectories and find that Manx shearwaters optimize their flight to increase the opportunity for dynamic soaring during favorable wind conditions. Our results show how small-scale dynamic soaring affects large-scale Manx shearwater distribution at sea.

Case Report of Puffinosis in a Manx Shearwater (Puffinus puffinus) Suggesting Environmental Aetiology.

Puffinosis is a disease of a range of seabirds characterised by dorsal and ventral blistering of their webbed feet, conjunctivitis, dry necrosis, leg spasticity, head shaking, loss of balance, tremors, and death. It is associated with Manx shearwaters (Puffinus puffinus), frequently affecting chicks within their underground nesting burrows. The aetiology of the disease is unclear but has been attributed to a type-2 coronavirus associated with Neotombicula mites as a potential vector. However, there is some uncertainty given potential laboratory contamination with mouse hepatitis virus and failure to fulfil Koch's postulates, with birds injected with isolates remaining healthy. We describe a detailed case report of puffinosis in a Manx Shearwater covering necropsy, histology, bacteriology, and metagenomics including viral sequencing. We found no evidence of viral infection or parasites. Our results are consistent with an entirely environmental aetiology, with caustic faecal ammonia in damp nesting burrows causing conjunctivitis and foot dermatitis breaking the skin, allowing common soil bacteria (i.e., Flavobacterium, Staphylococcus and Serratia spp., Clostridia perfringens and Enterococcus faecalis) to cause opportunistic infection, debilitating the bird and leading to death. A similar condition (foot pad dermatitis or FPD) has been reported in broiler chickens, attributed to caustic faeces, high humidity, and poor environmental conditions during indoor rearing, preventable by adequate ventilation and husbandry. This is consistent with puffinosis being observed in Shearwater nesting burrows situated in tall, dense, vegetation (e.g., bracken Pteridium aquilinum) but rarely reported in burrows situated in well-ventilated, short coastal grasslands. This proposed environmental aetiology accounts for the disease's non-epizootic prevalence, spatial variation within colonies, and higher frequency in chicks that are restricted to nesting burrows.

High turbidity levels alter coral reef fish movement in a foraging task.

Sensory systems allow animals to detect and respond to stimuli in their environment and underlie all behaviour. However, human induced pollution is increasingly interfering with the functioning of these systems. Increased suspended sediment, or turbidity, in aquatic habitats reduces the reactive distance to visual signals and may therefore alter movement behaviour. Using a foraging task in which fish (Rhinecanthus aculeatus) had to find six food sites in an aquarium, we tested the impact of high turbidity (40-68 NTU; 154 mg/L) on foraging efficiency using a detailed and novel analysis of individual movements. High turbidity led to a significant decrease in task efficacy as fish took longer to begin searching and find food, and they travelled further whilst searching. Trajectory analyses revealed that routes were less efficient and that fish in high turbidity conditions were more likely to cover the same ground and search at a slower speed. These results were observed despite the experimental protocol allowing for the use of alternate sensory systems (e.g. olfaction, lateral line). Given that movement underlies fundamental behaviours including foraging, mating, and predator avoidance, a reduction in movement efficiency is likely to have a significant impact on the health and population dynamics of visually-guided fish species.

Avoidance of different durations, colours and intensities of artificial light by adult seabirds.

There is increasing evidence for impacts of light pollution on the physiology and behaviour of wild animals. Nocturnally active Procellariiform seabirds are often found grounded in areas polluted by light and struggle to take to the air again without human intervention. Hence, understanding their responses to different wavelengths and intensities of light is urgently needed to inform mitigation measures. Here, we demonstrate how different light characteristics can affect the nocturnal flight of Manx shearwaters Puffinus puffinus by experimentally introducing lights at a colony subject to low levels of light pollution due to passing ships and coastal developments. The density of birds in flight above the colony was measured using a thermal imaging camera. We compared number of flying shearwaters under dark conditions and in response to an artificially introduced light, and observed fewer birds in flight during 'light-on' periods, suggesting that adult shearwaters were repelled by the light. This effect was stronger with higher light intensity, increasing duration of 'light-on' periods and with green and blue compared to red light. Thus, we recommend lower light intensity, red colour, and shorter duration of 'light-on' periods as mitigation measures to reduce the effects of light at breeding colonies and in their vicinity.

Consistent concentrations of critically endangered Balearic shearwaters in UK waters revealed by at-sea surveys.

AIM: Europe's only globally critically endangered seabird, the Balearic shearwater (Puffinus mauretanicus), is thought to have expanded its postbreeding range northwards into UK waters, though its at sea distribution there is not yet well understood. This study aims to identify environmental factors associated with the species' presence, map the probability of presence of the species across the western English Channel and southern Celtic Sea, and estimate the number of individuals in this area. LOCATION: The western English Channel and southern Celtic Sea. METHODS: This study analyses strip transect data collected between 2013 and 2017 from vessel-based surveys in the western English Channel and southern Celtic Sea during the Balearic shearwater's postbreeding period. Using environmental data collected directly and from remote sensors both Generalized Additive Models and the Random Forest machine learning model were used to determine shearwater presence at different locations. Abundance was estimated separately using a density multiplication approach. RESULTS: Both models indicated that oceanographic features were better predictors of shearwater presence than fish abundance. Seafloor aspect, sea surface temperature, depth, salinity, and maximum current speed were the most important predictors. The estimated number of Balearic shearwaters in the prediction area ranged from 652 birds in 2017 to 6,904 birds in 2014. MAIN CONCLUSIONS: Areas with consistently high probabilities of shearwater presence were identified at the Celtic Sea front. Our estimates suggest that the study area in southwest Britain supports between 2% and 23% of the global population of Balearic shearwaters. Based on the timing of the surveys (mainly in October), it is probable that most of the sighted shearwaters were immatures. This study provides the most complete understanding of Balearic shearwater distribution in UK waters available to date, information that will help inform any future conservation actions concerning this endangered species.

Natal imprinting to the Earth's magnetic field in a pelagic seabird.

In migratory animals for whom post-natal care is limited, it is essential that there are inherited mechanisms whereby an individual can navigate-first, to the terminus of their migration, and second, back to a suitable breeding site. In birds, empirical evidence suggests that orientation on first migration is controlled by an inherited navigational vector, a direction and a distance in which to move (the "clock and compass" model) [1-5]. The mechanism and information that underlie the return to the natal breeding site are, however, almost entirely unknown. A potential solution to this problem would be for an animal to learn the values for spatially and temporally stable gradient cues that specifically indicate the location of the natal site [6-16]. One potential cue for latitude is magnetic inclination. Here, we use ringing recoveries made over the last 80 years to investigate whether magnetic inclination might be used as a navigational cue to control the latitude of recruitment in a trans-global migrant, the Manx shearwater (Puffinus puffinus). We find that small changes in inclination between when a bird fledges and when it returns from first migration correlate with probabilistic changes in latitude at recruitment, in doing so quantitatively fulfilling a priori predictions as to the magnitude and direction of latitudinal shift. This, we believe, suggests that (1) natal magnetic inclination is learnt prior to fledging and (2) is used to provide latitudinal information when making the first return trip from the wintering grounds.

Short-term behavioural impact contrasts with long-term fitness consequences of biologging in a long-lived seabird.

Biologging has emerged as one of the most powerful and widely used technologies in ethology and ecology, providing unprecedented insight into animal behaviour. However, attaching loggers to animals may alter their behaviour, leading to the collection of data that fails to represent natural activity accurately. This is of particular concern in free-ranging animals, where tagged individuals can rarely be monitored directly. One of the most commonly reported measures of impact is breeding success, but this ignores potential short-term alterations to individual behaviour. When collecting ecological or behavioural data, such changes can have important consequences for the inference of results. Here, we take a multifaceted approach to investigate whether tagging leads to short-term behavioural changes, and whether these are later reflected in breeding performance, in a pelagic seabird. We analyse a long-term dataset of tracking data from Manx shearwaters (Puffinus puffinus), comparing the effects of carrying no device, small geolocator (GLS) devices (0.6% body mass), large Global Positioning System (GPS) devices (4.2% body mass) and a combination of the two (4.8% body mass). Despite exhibiting normal breeding success in both the year of tagging and the following year, incubating birds carrying GPS devices altered their foraging behaviour compared to untagged birds. During their foraging trips, GPS-tagged birds doubled their time away from the nest, experienced reduced foraging gains (64% reduction in mass gained per day) and reduced flight time by 14%. These findings demonstrate that the perceived impacts of device deployment depends on the scale over which they are sought: long-term measures, such as breeding success, can obscure finer-scale behavioural change, potentially limiting the validity of using GPS to infer at-sea behaviour when answering behavioural or ecological questions.

Manx shearwater (Puffinus puffinus) rafting behaviour revealed by GPS tracking and behavioural observations.

Before visiting or leaving their remote island colonies, seabirds often engage in a behaviour termed 'rafting', where birds sit, often in groups, on the water close to the colony. Despite rafting being a widespread behaviour across many seabird taxa, the functional significance of rafting remains unknown. Here we combine global positioning system (GPS) tracks, observational and wind condition data to investigate correlates of rafting behaviour in Manx shearwaters (Puffinus puffinus) at a large colony on Skomer Island, Wales. We test (1) the influence of wind direction on rafting location and (2) whether raft size changes with respect to wind speed. Our approach further allows us to describe day-night trends in (3) raft distance from shore through time; (4) the number of birds present in the nearshore waters through time; and (5) spatial patterns of Manx shearwater rafts in marine waters adjacent to the breeding colony. We find no evidence that wind direction, for our study period, influences Manx shearwater rafting location, yet raft size marginally increases on windier days. We further find rafting birds closer to the shore at night than during the day. Thus, before sunset, birds form a "halo" around Skomer Island, but this halo disappears during the night as more individuals return from foraging trips and raft nearer the colony on Skomer Island. The halo pattern reforms before sunrise as rafts move away from land and birds leave for foraging. Our results suggest that wind conditions may not be as ecologically significant for rafting locations as previously suspected, but rafting behaviour may be especially important for avoiding predators and cleaning feathers.

In Situ Clock Shift Reveals that the Sun Compass Contributes to Orientation in a Pelagic Seabird.

Compass orientation is central to the control of animal movement from the scale of local food-caching movements around a familiar area in parids [1] and corvids [2, 3] to the first autumn vector navigation of songbirds embarking on long-distance migration [4-6]. In the study of diurnal birds, where the homing pigeon, Columba livia, has been the main model, a time-compensated sun compass [7] is central to the two-step map-and-compass process of navigation from unfamiliar places, as well as guiding movement via a representation of familiar area landmarks [8-12]. However, its use by an actively navigating wild bird is yet to be shown. By phase shifting an animal's endogenous clock, known as clock-shifting [13-15], sun-compass use can be demonstrated when the animal incorrectly consults the sun's azimuthal position while homing after experimental displacement [15-17]. By applying clock-shift techniques at the nest of a wild bird during natural incubation, we show here that an oceanic navigator-the Manx shearwater, Puffinus puffinus-incorporates information from a time-compensated sun compass during homeward guidance to the breeding colony after displacement. Consistently with homing pigeons navigating within their familiar area [8, 9, 11, 18], we find that the effect of clock shift, while statistically robust, is partial in nature, possibly indicating the incorporation of guidance from landmarks into movement decisions.