Prey encounters and spatial memory influence use of foraging patches in a marine central place forager

Characterising underwater noise and changes in harbour porpoise behaviour during the decommissioning of an oil and gas platform

Many man-made marine structures (MMS) will have to be decommissioned in the coming decades. While studies on the impacts of construction of MMS on marine mammals exist, no research has been done on the effects of their decommissioning. The complete removal of an oil and gas platform in Scotland in 2021 provided an opportunity to investigate the response of harbour porpoises to decommissioning. Arrays of broadband noise recorders and echolocation detectors were used to describe noise characteristics produced by decommissioning activities and assess porpoise behaviour. During decommissioning, sound pressure spectral density levels in the frequency range 100 Hz to 48 kHz were 30-40 dB higher than baseline, with vessel presence being the main source of noise. The study detected small-scale (< 2 km) and short-term porpoise displacement during decommissioning, with porpoise occurrence increasing immediately after this. These findings can inform the consenting process for future decommissioning projects.

Back to the wild: movements of a juvenile tiger shark released from a public aquarium

Sharks are an important attraction for aquaria; however, larger species can rarely be kept indefinitely. To date, there has been little work tracking shark movements post-release to the wild. The authors used high-resolution biologgers to monitor a sub-adult tiger shark's pre- and post-release fine-scale movements following 2 years of captivity in an aquarium. They also compared its movement with that of a wild shark tagged nearby. Despite the differences in movement between the two sharks, with vertical oscillations notably absent and greater levels of turning seen from the released shark, the captive shark survived the release. These biologgers improve insight into post-release movements of captive sharks.

Movements and spatial usage of harbour seals in the Elbe estuary in Germany

Harbour seals are top predators in the North Sea and regarded as sentinels for ecosystem health. A few hundred also occur in adjacent estuaries, such as the Elbe estuary, Germany. However, only little is known about how these animals use this dynamic tidally influenced habitat, which has been under high anthropogenic pressure for decades. In this context, nine harbour seals (Phoca vitulina) from the Elbe estuary were equipped with biotelemetry devices to track their movements over multiple months. Harbour seal movements were characterised by short trips (trip length outside pupping season for females: 9.0 ± 1.12 km, males: 7.0 ± 1.24 km) as well as small home ranges (median 50% home range for females: 16.3 km², males: 36.1 km²) compared to harbour seals from marine regions. Within the estuary, the animals utilised the fairway, river branches and tributaries. During the pupping season in June and July, four seals showed strongly reduced trip lengths and durations, increased daily haul out durations as well as smaller home ranges. Even though a continuous exchange with harbour seals from the Wadden Sea likely occurs, most individuals in this study spent the entire deployment duration inside the estuary. This indicates that the Elbe estuary provides a suitable habitat for harbour seals, despite extensive anthropogenic usage, calling for further studies on the consequences of living in such an industrialised habitat.

Drivers of polar bear behavior and the possible effects of prey availability on foraging strategy

BACKGROUND

Change in behavior is one of the earliest responses to variation in habitat suitability. It is therefore important to understand the conditions that promote different behaviors, particularly in areas undergoing environmental change. Animal movement is tightly linked to behavior and remote tracking can be used to study ethology when direct observation is not possible.

METHODS

We used movement data from 14 polar bears (Ursus maritimus) in Hudson Bay, Canada, during the foraging season (January-June), when bears inhabit the sea ice. We developed an error-tolerant method to correct for sea ice drift in tracking data. Next, we used hidden Markov models with movement and orientation relative to wind to study three behaviors (stationary, area-restricted search, and olfactory search) and examine effects of 11 covariates on behavior.

RESULTS

Polar bears spent approximately 47% of their time in the stationary drift state, 29% in olfactory search, and 24% in area-restricted search. High energy behaviors occurred later in the day (around 20:00) compared to other populations. Second, olfactory search increased as the season progressed, which may reflect a shift in foraging strategy from still-hunting to active search linked to a shift in seal availability (i.e., increase in haul-outs from winter to the spring pupping and molting seasons). Last, we found spatial patterns of distribution linked to season, ice concentration, and bear age that may be tied to habitat quality and competitive exclusion.

CONCLUSIONS

Our observations were generally consistent with predictions of the marginal value theorem, and differences between our findings and other populations could be explained by regional or temporal variation in resource availability. Our novel movement analyses and finding can help identify periods, regions, and conditions of critical habitat.

Equivalence classification, learning by exclusion, and long-term memory in pinnipeds: cognitive mechanisms demonstrated through research with subjects under human care and in the field

Comparative cognition, as an interdisciplinary field, should utilize a holistic approach for studying cognitive mechanisms. We suggest that research with species of interest should employ both work with animals under human care and in the field. This complimentary approach allows for a better understanding of functional cognitive mechanisms themselves (i.e., comparative cognition regarding processes), and how these skill sets can relate to a particular species' ecological niche. We suggest that research evidence for equivalence classification, learning by exclusion, and long-term memory in pinnipeds can provide a foundation for discussion and implementation of a two-pronged methodological approach utilizing 'lab' and field' work. First, we describe evidence from research with pinnipeds under human care supporting each of these cognitive abilities, then follow this with evidence for implications of these mechanisms from complimentary field research. Lastly, we provide a brief discussion of implementation of a purposeful and two-pronged research approach as an understanding of pinnipeds' high levels of cognitive flexibility may underlie their success for navigating the ever-changing, and often human-altered, natural environment.

Desert Ants Learn to Avoid Pitfall Traps While Foraging

Simple Summary

Animals living in nests leave their nests to search for food and often use constant routes. We tested how workers of ant colonies cope with pitfall traps placed on their way to food. Such pits can represent those dug by the ant-hunting pit-building antlions. The pitfall traps delayed the arrival at the food and increased the workers’ tracks, but the ants improved in searching after accumulating experience. Furthermore, workers learned to avoid falling into the pits with experience. Removing or adding pits led to a fast change in the worker behavior and they ignored the past conditions, except for tracks that were longer than expected, after pitfall traps were removed. The ants fell much more frequently into pits closer to the arena entry, suggesting that such positions are especially profitable for sit-and-wait predators, ambushing such ants.

Abstract

Central-place foragers, such as social insects or nesting birds, repeatedly use the same routes from and to their nests when foraging for food. Such species forage more efficiently after accumulating experience. We examined, here, a relatively neglected aspect of such an improvement with experience—the avoidance of pitfall traps. Similar pits are built by antlions, which co-occur with the ants, but they also resemble other natural obstacles. We used the desert ant Cataglyphis niger, common in sandy habitats, and allowed it to forage for three successive runs for a food reward. Ant workers discovered food more slowly and in smaller numbers when pits were in their path. Pit presence also led to longer tracks by ants and slower movement. However, with experience, the ants fell into such pits less often and reached the food more quickly. To understand how past conditions affect current behavior, we investigated whether removing or adding pits led to a different result to that with a constant number of pits. Workers adjusted their behavior immediately when conditions changed. The only carryover effect was the longer tracks crossed by workers after pit removal, possibly resulting from the mismatch between the past and current conditions. Finally, the workers were more likely to fall into pits that were closer to the nest than those that were further away. This is a good example of the advantage that ambush predators can derive from ambushing their prey in specific locations.

Prey encounters and spatial memory influence use of foraging patches in a marine central place forager

Given the patchiness and long-term predictability of marine resources, memory of high-quality foraging grounds is expected to provide fitness advantages for central place foragers. However, it remains challenging to characterize how marine predators integrate memory with recent prey encounters to adjust fine-scale movement and use of foraging patches. Here, we used two months of movement data from harbour seals (Phoca vitulina) to quantify the repeatability in foraging patches as a proxy for memory. We then integrated these data into analyses of fine-scale movement and underwater behaviour to test how both spatial memory and prey encounter rates influenced the seals' area-restricted search (ARS) behaviour. Specifically, we used one month's GPS data from 29 individuals to build spatial memory maps of searched areas and archived accelerometery data from a subset of five individuals to detect prey catch attempts, a proxy for prey encounters. Individuals were highly consistent in the areas they visited over two consecutive months. Hidden Markov models showed that both spatial memory and prey encounters increased the probability of seals initiating ARS. These results provide evidence that predators use memory to adjust their fine-scale movement, and this ability should be accounted for in movement models.