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BACKGROUND: Lower limb mobility disabilities are well understood in older people, but the causes in middle age have attracted little attention. OBJECTIVES: To estimate the prevalence of mobility disabilities among noninstitutionalized adults in England and to compare the disabling symptoms reported by middle-aged and older people. DESIGN: Cross-sectional data from the 2002 English Longitudinal Study of Ageing (ELSA). Mobility disability was identified by level of reported difficulty walking a quarter mile. PARTICIPANTS: Eleven thousand two hundred sixteen respondents aged 50 years and older living in private households in 2002. RESULTS: The prevalence of difficulty walking a quarter mile increases sharply with age, but even in the middle-aged (50 to 64 years age-group) 18% (95% confidence interval [CI]: 16% to 19%) of men and 19% (95% CI: 17% to 20%) of women reported some degree of difficulty. Of the 16 main symptoms reported as causing mobility disability in middle age, 2 dominated: pain in the leg or the foot (43%; 95% CI: 40% to 46%) and shortness of breath/dyspnea (21%; 95% CI: 18% to 23%). Fatigue or tiredness, and stability problems were cited by only 5% and 6%, respectively. These proportions were slightly different from those in the 65 to 79-year age group: 40%, 23%, 6%, and 8%, respectively. CONCLUSIONS: Mobility (walking) disabilities in the middle-aged are relatively common. The symptoms reported as causes in this age group differ little from those reported by older groups, and are dominated by lower limb pain and shortness of breath. More clinical attention paid to disabling symptoms may lead to disability reductions in later life. [ABSTRACT FROM AUTHOR]

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 animal's 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.

For the first time, the flight paths of five butterfly species were successfully tracked using harmonic radar within an agricultural landscape. Until now, butterfly mobility has been predominantly studied using visual observations and mark-recapture experiments. Attachment of a light-weight radar transponder to the butterfly's thorax did not significantly affect behaviour or mobility. Tracks were analysed for straightness, duration, displacement, ground speed, foraging and the influence of linear landscape features on flight direction. Two main styles of track were identified: (A) fast linear flight and (B) slower nonlinear flights involving a period of foraging and/or looped sections of flight. These loops potentially perform an orientation function, and were often associated with areas of forage. In the absence of forage, linear features did not provide a guiding effect on flight direction, and only dense treelines were perceived as barriers. The results provide tentative support for non-random dispersal and a perceptual range of 100-200 m for these species. This study has demonstrated a methodology of significant value for future investigation of butterfly mobility and dispersal.