The definition and measurement of body condition are central to many ecological and evolutionary studies, yet the fundamental issue of whether variation in condition is inherited genetically remains unresolved. Furthermore, confusion has been caused through diverse uses of the word 'condition' itself In this paper, we introduce the terms 'broad-sense condition' and 'narrow-sense condition' in an attempt to reduce this confusion. Because of the difficulty of measuring condition, field biologists use the mass relative to body size as a convenient index of condition. Such indices have also been used to estimate the heritability of condition. Using data from a wild great tit Pants major population, we demonstrate that a condition index may still contain residual variance that is due to body size. Hence, using a condition index to study the heritability of condition can give misleading results because that residual variance may itself be heritable. To avoid this problem, direct measures of condition, such as reserve tissues, should be used. We provide the first heritability estimates of direct measures of condition of full-grown birds in a wild population by the regression of mean offspring (both in winter, and when breeding) on mean parent (when breeding) values of two reserve tissues, fat and pectoral muscle, which are independent of body-size. A great tit's fat and muscle reserves in winter were significantly correlated with their respective values when the birds bred. However there was no evidence that the level of fat reserves in winter resembled those of the parents (when breeding), more than expected by chance. Slight resemblances between parents and offspring were detected for muscle in winter and for fat reserves when breeding. Muscle size in the breeding season provided stronger evidence for the inheritance of condition.

Why do different species of birds start their dawn choruses at different times? We test the hypothesis that the times at which different species start singing at dawn are related to their visual capability at low light intensities. Birds with large eyes can achieve greater pupil diameters and hence, all other things being equal, greater visual sensitivity and resolution than birds with small eyes. We estimated the maximum pupil diameter of passerine birds by measuring the diameter of the exposed eye surface, and measured the times of the first songs at dawn of songbirds present in different bird communities, and the light intensities at these times. Using phylogenetic comparative analyses, we found that songbirds with large eyes started to sing at lower light intensities (and therefore earlier) than species with smaller eyes. These relationships were stronger when differences in body size were controlled for statistically, and were consistent between two phylogenies and when species were treated as independent data points. Our results therefore provide robust support for the hypothesis that visual capability at low light levels influences the times at which birds start to sing at dawn.

Aims: To investigate the effect of modern farming practices on the number of Corn Bunting breeding attempts. Methods: We compared the timing of breeding by Corn Buntings on the South Downs, West Sussex, with the habitat composition within 150 m of their nests. Results: Breeding was earlier in areas containing winter-sown wheat and set-aside than in areas containing spring-sown barley. Nests were earlier when cereal crops near the nest were more developed. The presence of unripe grain was a better predictor of the timing of breeding than the height of the crop. Double-brooding was extremely rare and few females re-laid after nest failures. Daily failure probabilities of clutches increased during the season, largely as a result of harvesting operations. Conclusions: Changes in the timing of cereal harvesting and the availability of uncultivated nesting habitat may have reduced the incidence of double-brooding in some intensive arable landscapes. Food availability may also limit the onset of breeding, further reducing the possibility of double-brooding.

Broods of fledgling robins Erithacus rubecula are sometimes divided between their parents so that each parent feeds only some of the chicks. These associations between a parent and certain of its young ('family units') are shown to be stable over periods of days. Brood division is most frequent in broods that are not followed by another nesting attempt. Experimental manipulation of the food supply suggests that brood division is relaxed when food is readily available. An analysis of the interactions between parents and chicks demonstrates that both adults and fledglings play a role in brood division. The possible functions of brood division are discussed with reference to 'other types of care', 'parental efficiency', 'cheat countermeasure' and 'two types of chick' hypotheses. Male parents feed chicks with shorter winglengths than do females: since females tend to have shorter winglengths than males, this suggests that chicks are cared for by parents of the opposite sex. Possible causes and consequences of this observation are discussed.

One of the many questions to which John Maynard Smith contributed was that of why most animal signals are reliable. He initially rejected the handicap argument but gradually accepted it, a process I briefly describe. This episode illustrated his preference for mathematical models over verbal ones, and the generosity with which he could change his mind. Even after accepting that some signals are reliable because of their strategic costs, he argued for a pluralistic approach to signal reliability. Signal complexity was a developing interest when he died. Signals usually involve several components, some of which appear to amplify other signal components. The terms amplifier and index require more thought to reduce the scope for semantic confusion. I conclude by describing Maynard Smith's fascination with peacocks Pavo cristatus.

I compared the feather mite (Acari, Proctophyllodidae) loads of moulting birds with features of the new plumage that they were growing. I examined 21 samples, each sample containing individuals of the same species, sex and age class (juvenile, yearling or adult). I used nine species: wren, Troglodytes troglodytes; dunnock, Prunella modularis; robin, Erithacus rubecula; blue tit, Parus caeruleus; great tit, P. major; chaffinch, Fringilla coelebs; greenfinch, Carduelis chloris; linnet, C. cannabina; and yellowhammer, Emberiza citrinella. As previously reported for the house finch, Carpodacus mexicanus, birds with more feather mites grew duller plumage and relatively shorter wings than less infested individuals of the same sex and age class. They also had lower protein reserves judged by the shape of their pectoral muscle. Mite load was usually a better predictor of coloration than pectoral muscle score, but the opposite was true for changes in wing length. In contrast to house finches, birds whose plumage was dull before moult had higher mite loads while moulting. Even if feather mites do not cause dull. plumage or short wings, they appear to be a good indicator of birds in poor physiological condition.

1. Corn buntings Miliaria calandra have declined steeply in Britain and north-western Europe since the mid-1970s; changes in farming practice are believed to have been partly responsible. 2. We studied nesting corn buntings on the South Downs in west Sussex between 1995 and 1997 to examine the possible effects of agricultural intensification on breeding success. The abundance of invertebrates around individual nests was sampled by sweep-netting in July. 3. Corn buntings provisioning nestlings foraged in grassy margins more than any other habitat relative to their availability within the maximum foraging range. The other habitats used more than expected were spring-sown barley, unintensified grass and set-aside. Those used less than expected included winter-sown wheat and intensively managed grassland. The invertebrates most commonly fed to chicks were more abundant in foraging areas than elsewhere. Their density was negatively correlated with the number of insecticide applications both when cereal fields only were considered and when all foraging habitats were included. 4. The lower the abundance of chick-food invertebrates close to nests, the greater the distance from the nest at which parents foraged, and the longer such trips were in duration. The weights of nestlings, corrected for age using tarsus length, were positively correlated with the abundance of chick-food invertebrates. 5. The probability of nest survival was negatively correlated with the abundance of chick-food invertebrates close to the nest, apparently as a result of an increased risk of predation. 6. Agricultural intensification in Britain, including the increased use of pesticides, has led to a widespread decrease in the availability of chick-food invertebrates on lowland farmland. If our results are typical of corn buntings in an arable environment, this decrease correlates with reduced breeding success. Depending on the mortality rates for fledged chicks and older birds, this reduction may have contributed to the corn buntings' decline and may hamper recovery. 7. Farming practices that increase invertebrate availability ought to benefit breeding corn buntings. Large-scale measures such as set-aside and the spring-sowing of cereals (especially if undersown with grass) depend heavily on overall agricultural policy. Small-scale initiatives might therefore be more feasible; these include the provision of grassy margins or beetle banks and selective spraying of headlands.

The diet of nestling Corn Buntings Miliaria calandra was assessed by examining 173 faeces collected from 39 broods on the South Downs in West Sussex. All faeces contained the remains of invertebrates and virtually all contained cereal grains. Arachnida (Araneae and Opiliones), Orthoptera, Lepidoptera (larvae), Symphyta (larvae) and Coleoptera (mainly adults) accounted for about 95% of the 720 invertebrates counted. There was no evidence that chick diet changed between 3 and 7 days after hatching. Late broods were fed more Orthoptera than early ones, the relative proportion of other dietary components remaining similar during the nesting season. In wet weather, faeces contained a higher proportion of grain. Even if decreases in chick food invertebrates over the last 25 years did not contribute to the decline of the Corn Bunting, they might hamper population recovery.