The colonisation of British cities by magpies is a recent phenomenon. This work presents an analysis of magpie breeding biology in the urban environment of south Manchester; laying date, nesting success, clutch size, incubation period, hatching success and nestling success have been investigated and where possible, are contrasted with the situation in rural areas. A proportion of magpies in Manchester renovate an old nest for the breeding attempt, a habit which is uncommon in rural populations. As a result of this, the average laying date for urban magpies is advanced relative to that of the surrounding rural areas. Another aspect of the urban breeding ecology which differed from that of rural magpies was the high frequency and success rate of repeat breeding attempts following an initial failure. These increased fledgling productivity by 25%, so that the average annual breeding sucess in the Manchester urban environment was 1·55 young per pair, which is one of the highest recorded for the magpie.

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Daily energy expenditure (DEE) of free‐living birds during the incubation and subsequent brood‐rearing stages was measured using the doubly‐labelled water technique for seven species of bird. These data are combined with published information to provide a data set of 17 species of bird covering the mass range 12–85 g. Allometric relationships between DEE and body mass for the two stages of breeding were constructed using three models (log‐transformation regression, geometric mean regression, and iterative non‐linear regression). The geometric mean regression model was rejected as inappropriate. The iterative non‐linear regression model provides the best predictions of DEE given the average body mass of a species, but is of less value for comparing data sets. The most commonly used model (log transformation regression) was thus favoured for comparative purposes as the predictions it generates do not significantly alter the conclusions that would be obtained with use of the iterative non‐linear regression models (Marquardt model) for the data sets in this work. Comparison between the average DEE for the two stages of breeding suggest higher DEE during the brood‐rearing period, although this was significant in only five species. The difference in body mass among species can account for more of the variation in average DEE during incubation (r2= 82·6%) than during brood‐rearing (r2= 67·3%1), indicating that other effects such as activity are probably more important determinants of energy expenditure during brood‐rearing. The residual variation in DEE during incubation, after the effect of body mass had been removed, was considered for groups of species occupying different ecological niches. It is shown that the level of activity and ambient temperature can explain much of the residual variation in DEE during incubation. The blue tit was used as an example to demonstrate the role of energy balance as a constraint on reproductive success during the incubation period.

Data on energy expenditure by 553 individuals of 28 species of small bird (10–150 g) are presented. All estimates of energy expenditure were obtained using the doubly‐labelled water technique. Intraspecies variation in daily energy expenditure was found to be positively correlated with brood provisioning rates, percentage of time flying and the frequency of non‐resting activity. Correlations were also shown with body‐mass, body‐size and several environmental factors. Published data on basal metabolic rates (BMR) sometimes differed substantially from estimates either made specifically as part of the studies considered here or calculated from allometric equations. For the purpose of interspecific comparisons, specific estimates of BMR are to be preferred. When expressed as a function of BMR, energy expenditures of free‐living birds ranged from 1 + to 7 + times BMR with a mode at 3 +. Values of daily energy expenditure exceeding 4 times BMR were found in up to 48% of species and 30% of individuals, so that, contrary to earlier suggestions, 4 times BMR is not a universal upper limit to the sustained work rate of small birds. Observed upper limits tended to be higher in species with energy‐expensive foraging habits. Energy expended by breeding birds is likely to involve a balance between the benefits a greater expenditure has for offspring production and any fitness penalty associated with the high level of energy expediture which nest provisioning involves.