Summary 1.Fat reserves are stored energy that may help birds survive periods of harsh winter weather. This hypothesis predicts that annual apparent survival is higher for birds with large fat reserves than for birds with few or no fat reserves in winter. 2. Blackbirds ( Turdus merula Linnaeus) were ringed in central Italy from 16 November to 20 February during 1990February during -2001. Fat scores were recorded for each bird. We used these capture-mark-recapture data for 1703 blackbirds to estimate the effect of large fat reserves on annual apparent survival, while controlling for transients, using computer programs  and  . Probability of birds retaining large fat reserves, or retaining few fat reserves, over 2 successive years was also estimated. 3. Birds with large fat reserves did not have higher estimated annual apparent survival than birds with few fat reserves ( 2 large = 2 few = 0·595, SE = 0·043), inconsistent with our prediction. No effects of age, sex or year were detected on annual apparent survival. Birds with few fat reserves in any given year tended to have few fat reserves the following year ( -few → large = 0·332, SE = 0·052). Birds with large fat reserves in any given year were unlikely to have large fat reserves the next year ( -large → few = 0·585, SE = 0·080). 4. Large fat reserves may not increase annual survival of blackbirds wintering in central Italy. Winter weather in our study area may be too mild to effect survival. Alternatively, increased predation risk associated with large fat reserves may counteract any benefits of reduced starvation risk.

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T he stress imposed to captured birds for research purposes (Calvo & Furness 1992) is justified by the fact that studies of bird migration and population dynamics based on the capture, marking and measuring of birds provide very important information for their conservation (Baillie et al. 1999). Moreover, the fact that experienced ringers capture, mark and measure birds is expected to reduce the stress caused to them. However, when mist-nets, which are used to capture birds, are kept open 24-hours a day (eg Pettersson 1986, Berthold et al. 1991, Pilastra & Spina 1997, problems for bird welfare may arise. The main problem is that, in order to extract the birds captured latest in the day, the last daily visit to mist-nets is carried out in the first darkness to avoid birds remaining in the nets all night. However, since they cannot be released in the dark (Bardi et al. 1983), diurnal birds must be released the morning after their capture and are thus forced to spend a night in captivity. This may have a number of negative effects. First, the condition of migrating birds using the area as a resting and fattening spot after long migration flights may be particularly sensitive to the stress of being kept overnight. Second, incubating and brooding individuals may lose their clutch and nestlings. Third, as newly-fledged altricial passerines are still dependent on their parents (O'Connor 1984), the separation might be hazardous for inexperienced birds. Fourth, many migrant species usually migrate at night (Berthold 1993) and thus being kept overnight during migration may interfere with the migrating behaviour of a bird. This may be particularly relevant in spring, when overnight captivity may delay the journey towards the breeding sites, thereby decreasing an individual's chances of obtaining a breeding territory and partner(s) of good quality (Alatalo et al. 1990, Tye 1992.Closing the mist-nets shortly before darkness allows the immediate release of the latest-caught birds, thus avoiding overnight captivity, but, at the same time, may reduce the number of birds caught and result in considerable loss of data. This is because the nocturnal closure of mist-nets may not only reduce the number of birds caught in the evening but also in early morning, the most productive time of the day (Gustin 1989, pers obs), due to the fact that re-opening the mist-nets before dawn might disturb the birds present around the mist-nets. The aim of this study was to assess the loss of evening and morning captures with nocturnal mist-net closure ie, when the last net round was eliminated. METHODSCaptures were carried out with a 300m mist-net transect from 16 April to 15 May of 1996-1998 at a Tyrrhenian coastal site in central Italy, Castelporziano presidential estate (41° 44' N12°24' E). In 1996 captures were carried out in an area of the estate characterised by agricultural land bordered and low scrub (hereafter area A). In 1997 and 1998 captures were carried out in a dunal area characterised by Mediterranean scrub (hereafter area B). In 19...