Sue Lewis

Evidence of intra-specific competition for food in a pelagic seabird

The factors affecting the population dynamics of seabirds have long intrigued biologists. Current data suggest that density-dependent depletion of prey during the breeding season may regulate population size. However, much of the evidence for this has been circumstantial, and the underlying mechanisms are unclear. Here, we show that the per capita population growth rates of northern gannet Morus bassanus at colonies in Britain and Ireland have declined with increasing population size. Furthermore, direct observations reveal that the mean foraging trip duration of breeding gannets is positively correlated with colony size, both among colonies of different sizes in the same year, and within colonies as they change in size. To understand this phenomenon, we have developed a model which demonstrates that disturbance of fish alone can readily generate conditions under which gannets at larger colonies have to travel further to obtain food.

Sex-specific foraging behaviour in a monomorphic seabird

Sexual differences in the foraging behaviour of parents have been observed in a number of sexually sizedimorphic birds, particularly seabirds, and the usual inference has been that these sex–specific differences are mediated primarily by differences in body size. To test this explanation, we compared the foraging behaviour of parents in a monomorphic seabird species, the northern gannet Morus bassanus. Using specially designed instruments and radio telemetry we found that individuals of both sexes were consistent in the directions and durations of their foraging trips. However, there were significant differences in the foraging behaviour of males and females. Female gannets were not only more selective than males in the areas where they foraged, but they also made longer, deeper dives and spent more time on the sea surface than males. As the sexes are morphologically similar in this species, then these differences are unlikely to have been mediated by body size. Our work highlights the need to investigate sexual differences in the foraging behaviour of seabirds and other species more closely, in order to test alternative theories that do not rely on differences in body size.

Evaluation of investigations to diagnose the cause of dizziness in elderly people: a community based controlled study.

Abstract Objective: To compare the findings in dizzy elderly people with those in controls of a similar age to identify which investigations differentiate dizzy from non-dizzy patients and to design an investigational algorithm. Design: Community based study of clinical and laboratory findings in dizzy and control elderly people. Setting: Research outpatient clinic at a teaching hospital. Subjects: 149 dizzy and 97 control subjects aged over 65 years recruited from a community survey and articles in the local press. Main outcome measures: Findings on physical examination, blood testing, electrocardiography (at rest and over 24 hours), electronystagmography, posturography, and magnetic resonance imaging of head and neck (125 (84%) dizzy subjects and 86 (89%) controls); hospital anxiety and depression score; responses to hyperventilation, carotid sinus massage, and the Hallpike manoeuvre. Results: Blood profile, electrocardiography, electronystagmography, and magnetic resonance imaging failed to distinguish dizzy from control subjects because of the frequency of asymptomatic abnormalities in controls. Posturography and clinical assessment (physical examination, dizziness provocation, and psychological assessment) showed significant differences between the groups. A cause of the dizziness was identified from clinical diagnostic criteria based on accepted definitions in 143 subjects, with 126 having more than one cause. The most common diagnoses were central vascular disease (105) and cervical spondylosis (98), often accompanied by poor vision and anxiety. Conclusion: Expensive investigations are rarely helpful in dizzy elderly people. The cause of the dizziness can be diagnosed in most cases on the basis of a thorough clinical examination without recourse to hospital referral. Key messages Expensive investigations are rarely helpful in the diagnosis of dizziness in elderly people The most common causes of dizziness in older people are central vascular disease and cervical spondylosis Poor vision and anxiety often accompany but are rarely the sole cause of dizziness These findings point to a definitive role for the general practitioner in the assessment of dizzy elderly patients

Stroke: a randomized trial of exercise or relaxation.

OBJECTIVES: To determine the feasibility and effect of exercise training after stroke.

Using behavioural and state variables to identify proximate causes of population change in a seabird

Changes in animal population size are driven by the interactions between intrinsic processes and extrinsic forces, and identifying the proximate mechanisms behind population change remains a fundamental question in ecology. Here we report on how measuring behavioural and state proxies of food availability among populations experiencing different growth rates can be used to rapidly identify proximate drivers of population trends. In recent decades, the Cape gannet Morus capensis has shown a major distributional shift with historically large colonies in Namibia decreasing rapidly, whilst numbers at South African colonies have increased, suggesting contrasting environmental conditions in the two regions. We compared per capita growth rates of five of the six extant colonies with foraging range (using miniaturised Global Positioning System loggers), foraging work rate, food delivery rates and body condition of breeding adults. We found significant associations between the rate of population change, individual behaviour, energetic gain and body condition that indicate that recent population changes are associated with extrinsic effects. This study shows that behavioural and state data can be used to identify important drivers of population change, and their cost-effectiveness ensures that they are an appealing option for measuring the health of animal populations in numerous situations.

Age‐related variation in reproductive traits in the wandering albatross: evidence for terminal improvement following senescence

The processes driving age-related variation in demographic rates are central to understanding population and evolutionary ecology. An increasing number of studies in wild vertebrates find evidence for improvements in reproductive performance traits in early adulthood, followed by senescent declines in later life. However, life history theory predicts that reproductive investment should increase with age as future survival prospects diminish, and that raised reproductive investment may have associated survival costs. These non-mutually exclusive processes both predict an increase in breeding performance at the terminal breeding attempt. Here, we use a 30-year study of wandering albatrosses (Diomedea exulans) to disentangle the processes underpinning age-related variation in reproduction. Whilst highlighting the importance of breeding experience, we reveal senescent declines in performance are followed by a striking increase in breeding success and a key parental investment trait at the final breeding attempt.

The Use of Pedometers in Stroke Survivors: Are They Feasible and How Well Do They Detect Steps?

OBJECTIVES To determine (1) the feasibility of pedometers for stroke patients and (2) the level of agreement between pedometers and actual step count. DESIGN Observational agreement study. SETTING Six stroke units. PARTICIPANTS Independently mobile stroke patients (N=50) ready for hospital discharge. INTERVENTIONS Patients were asked to apply 3 pedometers: 1 around the neck and 1 above each hip. Patients performed a short walk lasting 20 seconds, then a 6-minute walk test 6MWT. Video recordings determined the criterion standard step count. MAIN OUTCOME MEASURE Agreement between the step count recorded by pedometers and the step count recorded by viewing the criterion standard video recordings of the 2 walks. RESULTS Five patients (10%) needed assistance to put on the pedometers, and 5 (10%) could not read the step count. Thirty-nine (78%) would use pedometers again. Below a gait speed of about 0.5 m/s, pedometers did not generally detect steps. Agreement analyses showed that even above 0.5 m/s, pedometers undercounted steps for both the short walk and 6MWT; for example, the mean difference between the video recorder and pedometer around the neck was 5.93 steps during the short walk and 32.4 steps during the 6MWT. CONCLUSIONS Pedometers are feasible but generally do not detect steps at gait speeds below about 0.5 m/s, and they undercount steps at gait speeds above 0.5 m/s.

Is fatigue after stroke associated with physical deconditioning? A cross-sectional study in ambulatory stroke survivors

OBJECTIVE To determine the relationship between a measure of fatigue and 2 indices of physical fitness, lower limb extensor power (LLEP) and walking economy. DESIGN This was a cross-sectional study of patients with stroke. Fatigue was assessed by vitality (VIT) score of the Medical Outcomes Study 36-Item Short-Form Health Survey version 2 (SF-36v2). LLEP of the unaffected limb was measured using a lower leg extensor power rig. Walking economy was calculated by measuring oxygen consumption (mL·kg(-1)·m(-1)) during walking at a comfortable speed. Bivariate analyses were performed relating VIT to indices of fitness. Multiple regression analyses were also performed and included age, sex, and either SF-36v2 emotional role function or SF-36v2 mental health, as predictors of VIT. SETTING Community setting. PARTICIPANTS Participants (N=66; 36 men; mean age ± SD, 71.0±9.9y) were all community dwelling, had survived a stroke, were able to walk independently, and had completed their stroke rehabilitation. INTERVENTIONS Not applicable MAIN OUTCOME MEASURES The main outcome measure is SF-36v2 (VIT), with walking economy and LLEP of the limb unaffected by the stroke being independent variables. RESULTS Walking economy was not significantly related to VIT (R=-.024, P=.86, n=60). LLEP was positively related to VIT in bivariate analysis (R=.38, P=.003, n=58). After controlling for age, sex, and SF-36 emotional role function (or SF-36v2 mental health if the extreme outlier was excluded), LLEP remained a significant predictor of VIT. CONCLUSIONS We found an association between fatigue and reduced LLEP. If a larger study confirms these findings, it would support the need to develop and test interventions to increase LLEP as a treatment for fatigue after stroke.

Fitness increases with partner and neighbour allopreening

Altruism and selfishness are fundamental characteristics of human and animal societies. Among colonial biparental species, breeding outcome depends on interactions between mates and neighbours. However, the relationships between cooperation within and among partnerships and fitness have not been fully investigated. We show that in the highly colonial common guillemot (Uria aalge), altruistic behaviour (allopreening) towards a mate was positively related to long-term fitness, whereas allopreening a neighbour was related to current fitness. Turnover is much lower within than between pairs, so our results suggest that allopreening within pairs generates fitness returns at longer timescales than between pairs. Allopreening not only removes ectoparasites and maintains plumage condition, but may also have important social functions. We found a negative relationship between fight rate and allopreen rate between breeding neighbours, with nests exhibiting low breeding success having a higher frequency of fights with neighbours. We also found evidence for reciprocity in allopreening. Thus, allopreening may function as a reciprocal stress reducer, to decrease the likelihood of fights and associated breeding failure. We suggest that altruistic behaviour has long-term benefits for the survival of the offspring when living in a crowded neighbourhood.

Age-related variation in foraging behaviour in the wandering albatross at South Georgia: no evidence for senescence.

Age-related variation in demographic rates is now widely documented in wild vertebrate systems, and has significant consequences for population and evolutionary dynamics. However, the mechanisms underpinning such variation, particularly in later life, are less well understood. Foraging efficiency is a key determinant of fitness, with implications for individual life history trade-offs. A variety of faculties known to decline in old age, such as muscular function and visual acuity, are likely to influence foraging performance. We examine age-related variation in the foraging behaviour of a long-lived, wide-ranging oceanic seabird, the wandering albatross Diomedea exulans. Using miniaturised tracking technologies, we compared foraging trip characteristics of birds breeding at Bird Island, South Georgia. Based on movement and immersion data collected during the incubation phase of a single breeding season, and from extensive tracking data collected in previous years from different stages of the breeding cycle, we found limited evidence for age-related variation in commonly reported trip parameters, and failed to detect signs of senescent decline. Our results contrast with the limited number of past studies that have examined foraging behaviour in later life, since these have documented changes in performance consistent with senescence. This highlights the importance of studies across different wild animal populations to gain a broader perspective on the processes driving variation in ageing rates.