Evening mist‐net closure: Implications for data collection and bird welfare

Abstract

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...

“Feelings and Fitness” Not “Feelings or Fitness”–The Raison d'être of Conservation Welfare, Which Aligns Conservation and Animal Welfare Objectives

“…In accordance with this, welfare is often evaluated at the population level and using variables chiefly related to the physical state or biological function of the animals. At the most general level, welfare may be extrapolated from measures of survival and reproductive success, i.e., “ fitness” [e.g., ( 79 – 86 )].…”