What can seabirds tell us about the tide?

Abstract

Abstract. Small global positioning system (GPS) trackers are now routinely used to study the movement and behaviour of birds at sea. If the birds rest on the water they become “drifters of opportunity” and can be used to give information about surface currents. In this paper, we use a small data set from satellite-tracked razorbills (Alca torda) in the Irish Sea to test the potential of this idea for measuring tidal currents. Razorbills regularly rest on the sea overnight and their tracks at this time are consistent with their drifting with the tidal flows and changing direction as the flood turns to ebb and vice versa. Data from 4 years (2011–2014) have been binned in a geographical grid and analysed to give the variation of current over a mean tidal cycle in each grid element. A map of maximum current speed is consistent with a numerical model of the tidal currents in the region. The root mean square difference between observed maximum speed and that predicted by the model is 0.15 m s−1, about 15 % of typical current speeds in the area. The divergence between bird-track speed and model prediction increases in regions of the fastest tidal currents. The method clearly has its limitations, but the results of this study show that tagged birds resting on the sea have potential to provide relatively inexpensive quantitative information about surface tidal currents over an extended geographical area.

Buoys with looming eyes deter seaducks and could potentially reduce seabird bycatch in gillnets

“…We first explored whether the presence of LEBs can account for any variation in the counts of seabirds, and then tested specifically for an effect of LEB deployment in a before-after-control-impact (BACI) design analysis-a similar approach was adopted by Jiménez et al [42] in their study assessing seabird bycatch reduction in pelagic longline fleets. Counts of seabirds in a small area are subject to large temporal variation due to diurnal and seasonal movements, temporal disturbances, the influence of tidal currents, wind/weather factors, and other aspects that are difficult to measure [43][44][45]. Due to the large number of potential environmental factors that may affect seabird abundance and the fact that some of these variables may be correlated, we first conducted an exploratory analysis using an analytical approach that can accurately identify the relative importance of variables under these conditions [46][47][48].…”

Tidal drift removes the need for area-restricted search in foraging Atlantic puffins

“…We suggest that further studies combining diving behaviour and movement patterns are likely to confirm that non-ARS foraging is more widespread, particularly in areas of high tidal activity. Interestingly, a study on razorbills in Wales, UK, showed extensive periods of drift and little evidence of ARS, and while foraging behaviour was not the focus of that study [48], birds were diving during these trips (E. Owen 2019, personal communication).…”

The Use of Animal-Borne Biologging and Telemetry Data to Quantify Spatial Overlap of Wildlife with Marine Renewables

“…The speed threshold was chosen to account for the exceptional current speeds in the channel, regularly exceeding 3.5 m s −1 [45,57,58]. This means that birds drifting passively with the current, a behavior known as tidal drift, could realistically reach groundspeeds normally associated with flight [59][60][61]. An example R script for preparation, processing and analysis (steps 2-4 Figure 2) along with a dataset for one individual are provided in Appendix A and Supplementary Materials.…”

“…The blue shaded area (3.5-5 m/s) is the range of peak current speeds in the Pentland Firth [45,57,58]. Between 1 and 5 m/s, there is therefore a range of speeds that normally could be classified as flight but in this case could be tidal drift (bird sitting on the sea surface and drifting with the tide, [59][60][61]). The cautious approach would therefore be to set a speed threshold of >5 m/s.…”