Light data from geolocation reveal patterns of nest visit frequency and suitable conditions for efficient nest site monitoring in Common SwiftsApus apus

Abstract

Capsule: We developed a protocol for efficient monitoring of potential Common Swift Apus apus nest sites which considers variation in nest visit frequency across the breeding season and in relation to time of day and weather. Aims: To investigate patterns of nest visit frequency in Common Swifts in order to improve the efficiency and reliability of the monitoring of nest sites threatened by building renovations. Methods: We derived information on nest attendance from light data recorded by geolocators from ten adult Common Swifts during three breeding seasons (n = 686 individual sampling days) and analysed how nest visit frequency varied across the breeding season and in relation to time of day and weather. Results: The mean nest visit frequency was 5.63 visits per bird per day (0.32 visits per hour of daylight). The daily number of visits was highest at the beginning of July during chick-rearing. Moreover, it was positively correlated with temperature and negatively correlated with rainfall and wind speed. Nest visit frequency showed a distinct peak around sunset, while also being relatively high in the morning and around noon. Conclusion: We recommend monitoring potential Common Swift nest sites in Central Europe between the end of June and mid-July during good weather between 0.50 and 7.75 h after sunrise or between 3.00 h before sunset and sunset, when observation bouts of 0.5-2.0 h provide an encounter probability greater than 90%. Our study shows that repurposing geolocator light datausually used to study bird migrationfor investigating nest attendance in cavity-breeding birds can provide important information for bird conservation.

Cool birds: first evidence of energy-saving nocturnal torpor in free-living common swifts Apus apus resting in their nests

“…Since number of birds and total body mass in the nest are major determinants of normalV˙normalO2, we controlled for the number of parents present, from none to both adults at the nest, on nine of the 62 nights. We know from a previous study in the same colony [42] and other sites [27,28], that adults do not leave (or enter) the nest during darkness. Hence, we assumed that the number of birds did not vary during the calorimetric measurements.…”

No “carry-over” effects of tracking devices on return rate and parameters determining reproductive success in once and repeatedly tagged common swifts (Apus apus), a long-distance migratory bird

“…We recorded arrival dates as the first registration of birds detected by the antenna system. Additionally, we fixed an iButton ™ temperature logger (type DS1922L; accuracy ± 0.5 °C; Maxim Integrated ™ , USA) into the wall of each nest to measure nest temperature as a proxy for first use of the nest together with video surveillance using IR cameras (Conrad Electronics SE, Hirschau, Germany), and data from geolocators [49] to receive arrival dates. We investigated whether once or repeatedly tagging and/ or wing length and/or body mass have an effect on arrival date using linear regression models (relation weight and wing length to arrival) and a LMM with "year" as random effect to compare arrival of logger with non-logger birds.…”