To determine individual parental investment of an adult swift, each bird is tagged with a passive injectable transponder (EURO.I.D., Weilerswist, Germany). Time and duration of nest attendance of each individual is registered by means of ring-shaped antenna at nests and nest entrance holes (see study site). Thereby, you can obtain information, for instance, on length and duration of breeding phases and feeding frequency. For the latter, we observe additionally nests with infrared cameras. These data can be correlated to weather parameters or onset of laying (comparison of early and late breeders). Furthermore, we can determine by transpondering nestlings if and when a swift returns to its hatching place in following years, and when a swift starts with an own brood for the first time.