BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

During egg-formation, energy and protein are deposited in the developing eggs but are, at the same time, needed by the laying female herself. This has been largely overlooked in the discussion on income and capital breeders (Drent & Daan 1980, Thomas 1988. We discuss data on exogenous versus endogenous energy and nutrients used during eggformation for 12 well-studied species ranging from the Adelie Penguin Pygoscelis adelie (3400 g) to the Blue Tit Purus cueruleus (11 g) and calculate which part of the total energy and nutrient requirements (of clutch and laying female) originates from direct food intake and/or from body reserves. Because energy and nutrients are also needed by the laying female, some large species breeding in cold regions deposit sufficient reserve that they can fast completely during egg-formation (like the Adelie Penguin) and even throughout incubation (like the Eider Somateria mollissirnu). However, almost all smaller species must forage for most of their energy and nutrients during the egg-formation period. For the large species, energy and protein of the clutch represent 30% and 70%, respectively, of the total requirements of laying females, much more than in small species 0 1999 British Ornithologists' Union Poole 1985 B Food supplementation started before the breeding season, D. food supplementation started during the breeding season, L, food supplementation started during laying Period of food supplementation how many weeks food was added before laying started =Density-dependent effect one of 4 years a 40G increase S a m e controls for early and late feeding experiments dLarger eggs and clutches on one of two islands elncrease only by protein supplement 'No date correction Numbers in parenthesis have P level of 0 05-0 10, ns, not significant, 9, no data 1:) 1999 British Ornithologists Union Ibis, 141, 399-414

We relate variation in the timing of arrival by migrating birds breeding at northerly latitudes to individual differences in the prior accumulation of energy stores. Balancing starvation risks early in the season against the almost universal declining trend in reproductive prospects with advancing date is seen as an individual decision with fitness consequences. We review three studies implicating events at the staging sites or in winter in setting the individual migratory schedule. Climate change influences the timetable of a pied flycatcher (Ficedula hypoleuca) population breeding in The Netherlands and wintering in West Africa, followed since 1960. Mean air temperature in the period mid April‐mid May (arrival and laying) increased and laying date advanced by 10 days. Still, in recent years most birds did not lay early enough to maximise fitness (determined by recruitment and parental survival) whereas many parents achieved this goal in 1980–1985. As the flycatchers have not started to arrive earlier, some ecological constraint further upstream is postulated (possibly the hurdle of the crossing of Sahara and Mediterranean). The ability to follow individual migrants provides a second avenue to assess the fitness implications of migratory schedules. Thus, brightly coloured male bar‐tailed godwits (Limosa lapponica) captured in the Dutch Wadden Sea (the intermediate staging site linking a West African wintering area with breeding sites in arctic Russia) and traced with miniature radio‐transmitters did not depart early. The ‘best’ males (with bright breeding plumage) were picked up by the listening stations in Sweden 650 km further along the migratory route ten days later than the paler individuals. If early arrival confers the competitive advantage of prior occupancy but increases mortality, the ‘best’ males may be able to afford arriving later and thus avoid some of the survival costs. Return rate of the ‘bright’ males to the staging site in later seasons was indeed higher than for the ‘pale’, early males. Intensive observation of pink‐footed geese (Anser brachyrhynchus) fitted with coded neck‐collars substantiate the tight relationship between energy stores (fat) accumulated up to final departure from the final staging site (Vesterålen, N. Norway) en route to the nesting grounds (Spitsbergen) and subsequent success. The breeding outcome of individual parents (accompanied by juveniles or not) could be related to observations of body condition before departure (visual ‘abdominal profile index’). Recently, perceived conflicts with agriculture have resulted in widespread harassment by humans. The geese have: drastically shortened their stay on the Vesterålen, fail to achieve the body condition usual a decade ago and reproductive output has fallen. Although the geese are currently pioneering new staging sites, an adequate alternative has not materialised, underlining the critical role of the final take‐off site.

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Summary1. Mid-winter movements of up to several hundreds of kilometres are typical for many migratory bird species wintering in Africa. Unpredictable temporary food concentrations are thought to result in random movements of such birds, whereas resightings and recoveries of marked birds suggest some degree of site fidelity. Only detailed (e.g. satellite) tracking of individual migrants can reveal the relative importance and the causes of site choice flexibility and fidelity. The present study investigates how mid-winter movements of a Palaearctic-African migratory raptor, Montagu's harrier Circus pygargus, in the Sahel of West Africa are related to the availability of food resources. 2. Thirty harriers breeding or hatched in northern Europe were satellite tracked (2005)(2006)(2007)(2008)(2009)). On average, four home ranges, each separated by c. 200 km, were visited during one overwinter stay in the Sahel. Wintering home ranges were similar in size to breeding season home ranges (average over wintering and breeding home range size c. 200 km 2 ), and harriers showed high site fidelity between years. 3. Most preferred habitat types in the Sahel were mosaics of grass-and cropland, indicating similar habitat preferences in both the breeding-and wintering seasons. 4. The main prey of Montagu's harriers in the Sahel were grasshoppers Acrididae. Highest grasshopper numbers in the field occurred at relatively low vegetation greenness [normalized difference vegetation index (NDVI) values 0Á17-0Á27]. We used NDVI as a proxy of food availability for harriers. 5. During their overwinter stay, Montagu's harriers moved in a South-South-western direction between consecutive home ranges. The birds selected areas within the range of NDVI values associated with high grasshopper numbers, thus tracking a 'green belt' of predictable changes in highest grasshopper availability. 6. Contrary to earlier hypotheses of random movements in the Sahelian-wintering quarters, the present study shows that Montagu's harriers visited distinct home ranges, they were sitefaithful and tracked seasonal changes in food availability related to previous rainfall patterns, caused by the shifting Intertropical Convergence Zone. Itinerancy may be the rule rather than an exception among insectivorous birds wintering in African savannahs.