Resumen de Birds captured at automatic baited traps are heavier
Jordi Domènech, Juan Carlos Senar, M.J. Conroy
As with automatic trapping methods, funnel traps allow the ornithologist to trap birds while devoting time to other activities. In these methods, trapped birds remain within the trap until the investigator removes them. The time involved is always greater than for trpas idrectly activated by the investigator, because in the latter the birds can be taken out immediately after capture. In funnel traps, birds can feed on the bait for several minutes before they are extracted or realize that they have been trapped, and, as a consequence, one might methods. Here, we compare the body mass of birds captured at a specially designed funnel trap, which we described previously, with the corresponding results from a non-automatic platform trap. We analysed 953 captures of Serins Serinus serinus caught using this trap during the autumns of 1995-1997 in Barcelona, north-eastern Spain. Standardized body mass and number of seeds ingested (counted by visual inspection of the gullet through the skin) was higher for birds trapped in the funnel trap than for birds captured in the platform trap. Results also show that funnel and platform traps sam ple birds in an equivalent way in relation to sex, age and residence status, at least in autumn. Investigators should take into account this bias in body mass. The solution is simple: the investigator should visit the trap at brief intervals, in order to reduce the time available for captured birds to consume the bait.
