Evidence that dorsally mounted satellite transmitters affect migration chronology of Northern Pintails

Abstract

We compared migration movements and chronology between Northern Pintails (Anas acuta) marked with dorsally mounted satellite transmitters and pintails marked only with tarsus rings. During weekly intervals of spring and autumn migration between their wintering area in Japan and nesting areas in Russia, the mean distance that ringed pintails had migrated was up to 1000 km farther than the mean distance radiomarked pintails migrated. Radiomarked pintails were detected at spring migration sites on average 9.9 days (90 % CI 8.0, 11.8) later than ringed pintails that were recovered within 50 km. Although ringed and radiomarked pintails departed from Japan on similar dates, the disparity in detection of radiomarked versus ringed pintails at shared sites increased 7.7 days (90 % CI 5.2, 10.2) for each 1000 km increase in distance from Japan. Thus, pintails marked with satellite transmitters arrived at nesting areas that were 2500 km from Japan on average 19 days later than ringed birds. Radiomarked pintails were detected at autumn migration stopovers on average 13.1 days (90 % CI 9.8, 16.4) later than ringed birds that were recovered within 50 km. We hypothesize that dorsal attachment of 12-20 g satellite transmitters to Northern Pintails increased the energetic cost of flight, which resulted in more rapid depletion of energetic reserves and shortened the distance pintails could fly without refueling. Radiomarked pintails may have used more stopovers or spent longer periods at stopovers. causing their migration schedule to diverge from ringed pintails. We urge further evaluation of the effects of dorsally mounted transmitters on migration chronology of waterfowl.

Effects of harness-attached tracking devices on survival, migration, and reproduction in three species of migratory waterfowl

“…While we find a delay in timing of reproduction and possibly timing of migration for birds with harness-attached transmitters, the delay is only minor, and other aspects of migration or reproduction are not affected. In contrast with earlier studies, which have shown strong negative effects on migration timing and reproduction for birds equipped with tracking devices [20,33,35], we find that tracking devices are reliable tools to study timing of migration and reproduction, and the modified harness which we have developed appears to be a reliable method to attach tracking devices on geese. Given our different results for different sexes, we stress that researchers make a careful consideration which birds they equip with tracking devices.…”

“…Also, the migration speed of these birds was not affected. For comparison, an earlier study in northern pintails Anas acuta found that birds with harness-attached tracking devices arrived 19 days later on the breeding grounds in comparison with the population mean [20]. This is ascribed to a higher cost of migration, which is also suggested by models from Pennycuick et al [32].…”

“…Unfortunately, harnesses often have negative effects on birds, including reduced survival rates and reproductive success [16,39], reduced migratory flight speed [20], and changes in behavior [17]. Although many studies report on negative effects of harness attachment on a single behavioral aspect, few studies have addressed multiple potential negative effects simultaneously (but see [19]), such that the full range of potential negative effects can be explored.…”

Reduction in adverse effects of tracking devices on waterfowl requires better measuring and reporting

“…This is supported by Bowlin et al [9] who show that backpack attached geolocators on stuffed Common Swifts Apus apus increased drag and thus their flight ranges. Similarly, Hupp et al [39] found that Northern Pintails equipped with 12-20 g satellite transmitters [1-3% of the bird's body weight (BBW)] in East Asia build up a delay of 7.7 days per 1000 km during their migration compared to birds that were only ringed. Higher energetic costs during flight are given as a likely explanation.…”

“…For larger birds, it is sometimes possible to equip a control group with lightweight (< 1 g) geolocators on the colour rings, which can be used to measure migration variables such as moment of departure and arrival, and migration speed ( [22], Lameris et al unpublished). Yet, ring resightings and recoveries can also give useful estimates for comparison of some migration variables [39], such as the moment of arrival [8]. Observing birds after release can reveal differences in behaviour and short-term survival between the tagged group and the control group.…”