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

Abstract

Understanding how animals forage is a central objective in ecology. Theory suggests that where food is uniformly distributed, Brownian movement ensures the maximum prey encounter rate, but when prey is patchy, the optimal strategy resembles a Lévy walk where area-restricted search (ARS) is interspersed with commuting between prey patches. Such movement appears ubiquitous in high trophic-level marine predators. Here, we report foraging and diving behaviour in a seabird with a high cost of flight, the Atlantic puffin ( Fratercula arctica ), and report a clear lack of Brownian or Levy flight and associated ARS. Instead, puffins foraged using tides to transport them through their feeding grounds. Energetic models suggest the cost of foraging trips using the drift strategy is 28–46% less than flying between patches. We suggest such alternative movement strategies are habitat-specific, but likely to be far more widespread than currently thought.

Local prey shortages drive foraging costs and breeding success in a declining seabird, the Atlantic puffin

“…Flight costs are extremely high in auks (Elliott et al., 2013) so flight has a key impact on energy expenditure. Consistent with this, studies suggest that chick‐rearing puffins usually feed within 25 km of the colony (Bennison et al., 2019; Harris et al., 2012). However, in our study, puffins fed near the colony but also much further, and used a dual foraging mode combining short and long trips, with the negative relationship between trip range and breeding success holding for both types of trips.…”

“…Time in flight was strongly correlated with trip range (LMM, = 89.1, p < 0.001, R 2 = 0.57); therefore, flight time per trip differed between colonies (Figure 2c, LMM, = 21.9, p < 0.001, R 2 = 0.33). Most flight occurred in a few sustained bouts (short trips: 2.7 ± 0.1 bouts; long trips: 4.9 ± 0.4 bouts) suggesting that birds flew out to a feeding area, then spent most of the time sitting on the water and diving in a ‘tidal‐drift’ tactic (Bennison et al., 2019), rather than engaging in area‐restricted search (this is also visible from the tracks, Figure S5). Across all colonies, foraging effort was consistently higher on long trips than on short trips, but there were no differences between colonies (LMM, short vs. long: = 61.8, p < 0.001, R 2 = 0.48; colony: = 2.7, p = 0.253; R 2 = 0.48), although it seemed to increase on long trips from northern Iceland to Norway (Table 2; Figure 2d).…”

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.…”

Assessing the effectiveness of foraging radius models for seabird distributions using biotelemetry and survey data

“…Terns have a high level of variability in foraging modes (Eglington et al 2014) both within and across years, and appear to rely on trophic level segregation rather than spatial segregation to avoid competition (Robertson et al 2014). Although foraging auks are known to associate with discrete features in the environment, such as tidal currents (Waggitt et al 2016, Bennison et al 2019, auk distribution is generally closely linked to distance to colony (Johnston et al 2015). Furthermore, sympatric auk species also rely on niche segregation rather than spatial segregation during the breeding season (Linnebjerg et al 2013, Shoji et al 2015b).…”