DOI: 10.5061/dryad.961nn65
title: Data from: Carrying a logger reduces escape flight speed in a passerine bird, but relative logger mass may be a misleading measure of this flight performance detriment

description: 1. The recent boost in bird migration studies following the development of
 various tracking devices raised awareness of how detrimental attaching
 devices can be for animals. Such effects can occur during migration, but
 also immediately post-release if the device impairs escape flight
 performance and, consequently, the bird’s ability to evade predators. 2.
 In this study, we investigated the effect of carrying a device on the
 escape flight speed and aerodynamic force production in a migratory
 passerine. We recorded upward-directed escape flights of 15 male
 blackcaps. Each individual was tested without a tag, and when equipped
 with three different leg-loop dummy tags with masses representing around
 3%, 5% and 7% of their body mass. The experiment was designed such that
 all individuals passed through all treatments in a randomized order. 3. We
 found that two factors affected flight speed in roughly equal amounts:
 first, tagged escape flights had lower flight speeds compared to the
 control flights, irrespective of tag mass. Second, we found an effect of
 the total mass, i.e. the sum of the masses of the individual bird and of
 the tag, with heavier birds being slower. In contrast, flight speed was
 not correlated with relative tag mass in percentage of body mass, the
 metric commonly used in ethical guidelines for tag attachment. Aerodynamic
 flight force production also depended on total mass, with heavier birds
 producing higher forces. But these flight forces did not differ between
 flights with or without a tag. 4. We conclude that, when tagging birds, it
 is misleading to choose heavy individuals for tagging in order to minimize
 the tag mass as a percentage of body mass. This is particularly relevant
 in species for which body mass is not necessarily related to size, like
 migratory birds that accumulate large fat reserves. The lower escape speed
 in “tagged” flights could not be explained by differences in net flight
 force production, because these did not differ between flights with and
 without a tag. This suggests that the tag also affected pre-flight
 take-off dynamics, possibly due to a leg harness-induced reduction in leg
 push-off performance.
description: Flight performance
 metrics, treatment information and flight tracks of the upward-directed
 flight manoeuvres of blackcapsFlight performance
 metrics, treatment information and flight tracks of all analysed
 upward-directed escape flight manoeuvres of blackcaps with and without a
 tag. The database is provided in a MATLAB (MathWorks, Inc.) binary data
 container format. Each flight manoeuvre is identified by the combination
 calendar date and sequence number. Flight performance metrics are flight
 speed, vertical flight speed, net aerodynamic force, vertical component of
 the net force, ascend angle and tortuosity. The treatment information
 consists of all data associated with the blocked experimental design
 (Table S1), including bird ID number, flight day (day 1 to 5), treatment
 (control, light tag, medium tag, or heavy tag), and mass information (bird
 mass, harness mass, tag mass and total mass of bird, harness and tag
 combined, in grams). The flight track data consists of the bird’s beak
 position throughout each escape manoeuvre, described by the
 Kalman-filtered X={x,y,z} coordinates (in meters, as defined in Figure 1)
 throughout time t (in seconds).FlightTracks_TreatmentInfo_FlightPerformance.mat