Jessica Meade

Migration and stopover in a small pelagic seabird, the Manx shearwater Puffinus puffinus: insights from machine learning

The migratory movements of seabirds (especially smaller species) remain poorly understood, despite their role as harvesters of marine ecosystems on a global scale and their potential as indicators of ocean health. Here we report a successful attempt, using miniature archival light loggers (geolocators), to elucidate the migratory behaviour of the Manx shearwater Puffinus puffinus, a small (400 g) Northern Hemisphere breeding procellariform that undertakes a trans-equatorial, trans-Atlantic migration. We provide details of over-wintering areas, of previously unobserved marine stopover behaviour, and the long-distance movements of females during their pre-laying exodus. Using salt-water immersion data from a subset of loggers, we introduce a method of behaviour classification based on Bayesian machine learning techniques. We used both supervised and unsupervised machine learning to classify each birds daily activity based on simple properties of the immersion data. We show that robust activity states emerge, characteristic of summer feeding, winter feeding and active migration. These can be used to classify probable behaviour throughout the annual cycle, highlighting the likely functional significance of stopovers as refuelling stages.

Homing pigeons develop local route stereotypy.

The mechanisms used by homing pigeons (Columba livia) to navigate homeward from distant sites have been well studied, yet the mechanisms underlying navigation within, and mapping of, the local familiar area have been largely neglected. In the local area pigeons potentially have access to a powerful navigational aid--a memorized landscape map. Current opinion suggests that landmarks are used only to recognize a familiar start position and that the goalward route is then achieved solely using compass orientation. We used high-resolution global positioning system (GPS) loggers to track homing pigeons as they became progressively familiar with a local homing task. Here, we demonstrate that birds develop highly stereotyped yet individually distinctive routes over the landscape, which remain substantially inefficient. Precise aerial route recapitulation implies close control by localized geocentric cues. Magnetic cues are unlikely to have been used, since recapitulation remains despite magnetic disruption treatment, and olfactory cues would have been positionally unstable under the variable wind conditions, making visual landmarks the most likely cues used.

Pigeons combine compass and landmark guidance in familiar route navigation

How do birds orient over familiar terrain? In the best studied avian species, the homing pigeon (Columba livia), two apparently independent primary mechanisms are currently debated: either memorized visual landmarks provide homeward guidance directly, or birds rely on a compass to home from familiar locations. Using miniature Global Positioning System tracking technology and clock-shift procedures, we set sun-compass and landmark information in conflict, showing that experienced birds can accurately complete their memorized routes by using landmarks alone. Nevertheless, we also find that route following is often consistently offset in the expected compass direction, faithfully reproducing the shape of the track, but in parallel. Thus, we demonstrate conditions under which compass orientation and landmark guidance must be combined into a system of simultaneous or oscillating dual control.

Objectively identifying landmark use and predicting flight trajectories of the homing pigeon using Gaussian processes.

Pigeons home along idiosyncratic habitual routes from familiar locations. It has been suggested that memorized visual landmarks underpin this route learning. However, the inability to experimentally alter the landscape on large scales has hindered the discovery of the particular features to which birds attend. Here, we present a method for objectively classifying the most informative regions of animal paths. We apply this method to flight trajectories from homing pigeons to identify probable locations of salient visual landmarks. We construct and apply a Gaussian process model of flight trajectory generation for pigeons trained to home from specific release sites. The model shows increasing predictive power as the birds become familiar with the sites, mirroring the animals learning process. We subsequently find that the most informative elements of the flight trajectories coincide with landscape features that have previously been suggested as important components of the homing task.

Ecological and demographic correlates of helping behaviour in a cooperatively breeding bird

The evolution of cooperation is a persistent problem for evolutionary biologists. In particular, understanding of the factors that promote the expression of helping behaviour in cooperatively breeding species remains weak, presumably because of the diverse nature of ecological and demographic drivers that promote sociality. In this study, we use data from a long-term study of a facultative cooperative breeder, the long-tailed tit Aegithalos caudatus, to investigate the factors influencing annual variation in helping behaviour. Long-tailed tits exhibit redirected helping in which failed breeders may become helpers, usually at a relatives nest; thus, helping is hypothesised to be associated with causes of nest failure and opportunities to renest or help. We tested predictions regarding the relationship between annual measures of cooperative behaviour and four explanatory variables: nest predation rate, length of the breeding season, population-level relatedness and population density. We found that the degree of helping was determined principally by two factors that constrain successful independent reproduction. First, as predicted, cooperative behaviour peaked at intermediate levels of nest predation, when there are both failed breeders (i.e. potential helpers) and active nests (i.e. potential recipients) available. Second, there were more helpers in shorter breeding seasons when opportunities for renesting by failed breeders are more limited. These are novel drivers of helping behaviour in avian cooperative breeding systems, and this study illustrates the difficulty of identifying common ecological or demographic factors underlying the evolution of such systems.

An Experimental Test of the Information Model for Negotiation of Biparental Care

Background Theoretical modelling of biparental care suggests that it can be a stable strategy if parents partially compensate for changes in behaviour by their partners. In empirical studies, however, parents occasionally match rather than compensate for the actions of their partners. The recently proposed “information model” adds to the earlier theory by factoring in information on brood value and/or need into parental decision-making. This leads to a variety of predicted parental responses following a change in partner work-rate depending on the information available to parents. Methodology/Principal Findings We experimentally test predictions of the information model using a population of long-tailed tits. We show that parental information on brood need varies systematically through the nestling period and use this variation to predict parental responses to an experimental increase in partner work-rate via playback of extra chick begging calls. When parental information is relatively high, partial compensation is predicted, whereas when parental information is low, a matching response is predicted. Conclusions/Significance We find that although some responses are consistent with predictions, parents match a change in their partners work-rate more often than expected and we discuss possible explanations for our findings.

Brood sex ratio variation in a cooperatively breeding bird.

In cooperatively breeding species, the fitness consequences of producing sons or daughters depend upon the fitness impacts of positive (repayment hypothesis) and negative (local competition hypothesis) social interactions among relatives. In this study, we examine brood sex allocation in relation to the predictions of both the repayment and the local competition hypotheses in the cooperatively breeding long‐tailed tit Aegithalos caudatus. At the population level, we found that annual brood sex ratio was negatively related to the number of male survivors across years, as predicted by the local competition hypothesis. At an individual level, in contrast to predictions of the repayment hypothesis, there was no evidence for facultative control of brood sex ratio. However, immigrant females produced a greater proportion of sons than resident females, a result consistent with both hypotheses. We conclude that female long‐tailed tits make adaptive decisions about brood sex allocation.

Route recognition in the homing pigeon, Columba livia

While homing pigeons are known to use familiar visual landmarks to recognize release sites, it is less clear whether they continue to attend to visual cues along the homeward flight. To address this question, we used precision GPS technology to track pigeons along their homeward route and later released them from sites that they were known to have flown over. The group of birds that were aerially familiar with the chosen sites homed significantly more efficiently than did their yoked (naive) counterparts. We found no evidence that birds were able to recognize sites that they had previously flown over from the substantially different viewpoint perceived at ground level. The results imply that the birds were able to recognize some aspect of the chosen sites after release and used this information to home more efficiently, although the nature of these cues is not clear.

Landscape complexity influences route-memory formation in navigating pigeons

Observations of the flight paths of pigeons navigating from familiar locations have shown that these birds are able to learn and subsequently follow habitual routes home. It has been suggested that navigation along these routes is based on the recognition of memorized visual landmarks. Previous research has identified the effect of landmarks on flight path structure, and thus the locations of potentially salient sites. Pigeons have also been observed to be particularly attracted to strong linear features in the landscape, such as roads and rivers. However, a more general understanding of the specific characteristics of the landscape that facilitate route learning has remained out of reach. In this study, we identify landscape complexity as a key predictor of the fidelity to the habitual route, and thus conclude that pigeons form route memories most strongly in regions where the landscape complexity is neither too great nor too low. Our results imply that pigeons process their visual environment on a characteristic spatial scale while navigating and can explain the different degrees of success in reproducing route learning in different geographical locations.

Do parents and helpers adjust their provisioning effort in relation to nestling sex in a cooperatively breeding bird

In cooperatively breeding vertebrates, investment strategies of breeders and helpers may be affected by the sex of offspring that they provision because the fitness benefits gained from caring for sons or daughters will depend upon the fitness impacts of positive (i.e. local resource enhancement) and negative (i.e. local resource competition) social interactions between relatives. We investigated the relationship between provisioning effort by breeders and helpers and the sex of nestlings that they provision, using long-term data over 16 years and detailed behavioural observation of interactions between carers and offspring in a cooperatively breeding species, the long-tailed tit, Aegithalos caudatus . We predicted preferential care for male nestlings because males are the more helpful sex in the kin-selected social system of long-tailed tits. However, we found that despite the significant size difference between male and female nestlings, there was no evidence of facultative adjustment of provisioning effort by either breeders or helpers in relation to brood sex ratio. In addition, we found no evidence for sex-biased provisioning by carers, and no bias in the feeds received by nestlings according to their sex. Thus, we conclude that the provisioning strategy of long-tailed tits does not incorporate differential investment according to sex. We suggest that the unpredictable nature of helping in the atypical cooperative breeding system of long-tailed tits makes random provisioning effort in relation to nestling sex the best option for carers.