From Sensor Data to Animal Behaviour: An Oystercatcher Example

Animal-borne sensors enable researchers to remotely track animals, their physiological state and body movements. Accelerometers, for example, have been used in several studies to measure body movement, posture, and energy expenditure, although predominantly in marine animals. In many studies, behaviour is often inferred from expert interpretation of sensor data and not validated with direct observations of the animal. The aim of this study was to derive models that could be used to classify oystercatcher (Haematopus ostralegus) behaviour based on sensor data. We measured the location, speed, and tri-axial acceleration of three oystercatchers using a flexible GPS tracking system and conducted simultaneous visual observations of the behaviour of these birds in their natural environment. We then used these data to develop three supervised classification trees of behaviour and finally applied one of the models to calculate time-activity budgets. The model based on accelerometer data developed to classify three behaviours (fly, terrestrial locomotion, and no movement) was much more accurate (cross-validation error = 0.14) than the model based on GPS-speed alone (cross-validation error = 0.35). The most parsimonious acceleration model designed to classify eight behaviours could distinguish five: fly, forage, body care, stand, and sit (cross-validation error = 0.28); other behaviours that were observed, such as aggression or handling of prey, could not be distinguished. Model limitations and potential improvements are discussed. The workflow design presented in this study can facilitate model development, be adapted to a wide range of species, and together with the appropriate measurements, can foster the study of behaviour and habitat use of free living animals throughout their annual routine

Unexpected diversity in socially synchronized rhythms of shorebirds

The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment1, 2, 3, 4. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions1, 5, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators6, 7, 8, 9, 10. Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring)6, 7, 8, 9, 11. The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood5, 6, 7, 9. Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization12 where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within- and between-species diversity in incubation rhythms. Between species, the median length of one parent’s incubation bout varied from 1–19 h, whereas period length—the time in which a parent’s probability to incubate cycles once between its highest and lowest value—varied from 6–43 h. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or who actively protect their nest against predators. Rhythms entrainable to the 24-h light–dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity5, 6, 7, 9. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms

Is the Bill of the Male Oystercatcher a Better Tool for Attacking Mussels Than the Bill of the Female?

Male Oystercatchers, Haematopus ostralegus, take relatively more large and thick-shelled molluscs, like cockles and mussels, while female Oystercatchers take relatively more deeply buried clams and polychaetes. Opening sturdy prey requires considerable muscular effort and the bill must be strong to resist the stresses. Sexual dimorphism in bill morphology is subtle and consists of the following: the bill of the male is shorter in total length and the distal half (gonys-region) is deeper and wider, suggesting it is stronger in resisting forces operating on the bill when opening mussels. Skull dimensions and the weight of the depressor muscle of the beak Musculus depressor mandibulae do not differ between the sexes. It is argued that with equal effort of the head, neck and jaw muscles, greater forces are exerted at the contact point between the bill and the prey in the male bill than in the female to overcome the resistance required to open mussels

Is the Bill of the Male Oystercatcher a Better Tool for Attacking Mussels Than the Bill of the Female?

Male Oystercatchers, Haematopus ostralegus, take relatively more large and thick-shelled molluscs, like cockles and mussels, while female Oystercatchers take relatively more deeply buried clams and polychaetes. Opening sturdy prey requires considerable muscular effort and the bill must be strong to resist the stresses. Sexual dimorphism in bill morphology is subtle and consists of the following: the bill of the male is shorter in total length and the distal half (gonys-region) is deeper and wider, suggesting it is stronger in resisting forces operating on the bill when opening mussels. Skull dimensions and the weight of the depressor muscle of the beak Musculus depressor mandibulae do not differ between the sexes. It is argued that with equal effort of the head, neck and jaw muscles, greater forces are exerted at the contact point between the bill and the prey in the male bill than in the female to overcome the resistance required to open mussels

Territory Quality, Parental Effort and Reproductive Success of Oystercatchers (Haematopus ostralegus)

1. Oystercatchers that breed on the saltmarsh of the Frisian island of Schiermon-nikoog occupy two different types of territory. In 'resident' territories the nesting area and the feeding area are adjacent. In 'leapfrog' territories the nesting area and the feeding area are separated by distances of 200-500 m. 2. Between 1984 and 1989, residents fledged on average 3.5 times as many chicks per year as leapfrogs. 3. The discrepancy in fledgling production arose primarily through increased mortality of leapfrog chicks due to starvation. This was indicated by low body weights of leapfrog chicks found dead and successful enhancement of leapfrog chick growth through supplementary food. In addition, the presence of a sibling reduced the probability of fledging for leapfrog chicks, but not for resident chicks, providing further evidence that leapfrog chicks competed for a limited food supply. 4. Leapfrog parents fledged fewer chicks, not because of poor feeding conditions in their feeding territory (intake rates of leapfrogs exceeded those of residents), but because they failed to transport a sufficient amount of food to the chicks. To supply their chicks with the same amount of food as did residents, leapfrog parents should have spent c. 4000 s per low water period in transport flights: no leapfrog parent ever reached this level of effort. 5. Our data show that it is not correct to equate parental effort to the number of chicks raised, as territories of different quality require different levels of effort for successful reproduction

Why do Oystercatchers Haematopus ostralegus switch from feeding on Baltic tellin Macoma balthica to feeding on the ragworm Nereis diversicolor during the breeding season?

Oystercatchers Haematopus ostralegus breeding on the isle of Schiermonnikoog in the Dutch Wadden Sea: switched from a diet dominated by the bivalve Macoma balthica in late spring to a diet dominated by the annelid worm Nereis diversicolor in early summer. Although all Oystercatchers switched, the timing and the magnitude of the switch differed between individuals. Since searching for Macoma appeared incompatible with searching for Nereis, we expected individuals to search for the prey species yielding the highest intake rate for a given period in the season. Some analyses clearly supported this suggestion, while the results of others were at best ambiguous. Although the density of large Macon!a did not change, the intake rate of Macoma declined during the summer, due to a decline in the capture rate of Macoma. This may have resulted from an increase in the burying depth and a decline in the condition of Macoma, as this forced the Oystercatchers to prey on an increasingly smaller fraction of the Macoma population. Intake rate on Nereis was not related to the density of Nereis, which tripled during the course of the study in 1986, while intake rate seemed to decline in late summer after having reached a peak in early summer. This peak was possibly due to a high surface activity of Nereis. Thus, the diet switch may have been due to an increase in the burying depth and a decline in the condition of. Macoma, or to an increase in the surface activity of Nereis, or both. Problems of interpretation arose primarily from the consistent differences between individuals in prey choice and the lack of independent measures of prey availability