Oceanic thermal structure mediates dive sequences in a foraging seabird

Abstract

Changes in marine ecosystems are easier to detect in upper‐level predators, like seabirds, which integrate trophic interactions throughout the food web. Here, we examined whether diving parameters and complexity in the temporal organization of diving behavior of little penguins (Eudyptula minor) are influenced by sea surface temperature (SST), water stratification, and wind speed—three oceanographic features influencing prey abundance and distribution in the water column. Using fractal time series analysis, we found that foraging complexity, expressed as the degree of long‐range correlations or memory in the dive series, was associated with SST and water stratification throughout the breeding season, but not with wind speed. Little penguins foraging in warmer/more‐stratified waters exhibited greater determinism (memory) in foraging sequences, likely as a response to prey aggregations near the thermocline. They also showed higher foraging efficiency, performed more dives and dove to shallower depths than those foraging in colder/less‐stratified waters. Reductions in the long‐term memory of dive sequences, or in other words increases in behavioral stochasticity, may suggest different strategies concerning the exploration–exploitation trade‐off under contrasting environmental conditions.

The consequences of chaos: Foraging activity of a marine predator remains impacted several days after the end of a storm

“…The latter is what we suspect happened in our study: the storm changed the thermal structure of the water column; a deepening of the mixed layer being indicative of a deepening or disappearing of the thermocline. Strong wind and changes in the thermal stratification of the water column reduced the ability of little penguins to capture prey efficiently [ 7 – 10 , 39 ], as also shown in African penguins ( Spheniscus demersus ) [ 40 ]. Birds increased their foraging effort through either a deepening of the dive depth (African penguins) or increased trip duration, a greater diving activity and a shorter time spent encountering prey (little penguins).…”

“…However, thermal stratification can vary in space and time within years or weeks in the foraging areas of these birds [ 7 , 8 ]. In addition, one-off events, such as strong winds and storms, may increase the mixing of the water column, leading to the weakening or total disappearance of the thermocline [ 7 ] and, consequently, affecting little penguins’ foraging efficiency [ 9 , 10 ].…”

To draw or not to draw: understanding the temporal organization of drawing behaviour using fractal analyses

“…To investigate long-memory processes in the sequential distribution of drawing and non-drawing durations, we employed Detrended Fluctuation Analysis (DFA) (Peng et al, 1995) which is among the most used to study binary sequences of animal behaviour (MacIntosh et al, 2013;Meyer et al, 2020;Rutherford et al, 2003). It is also a robust estimator of the Hurst exponent (Cannon et al, 1997;Eke et al, 2002).…”

“…Some environmental pressures or physiological impairments can lead to a loss of complexity in the behavioural sequences of an individual, associated with increases in periodicity or long-range dependence (i.e. greater stereotypy) (MacIntosh et al, 2011;Marıa et al, 2004;Meyer et al, 2020). Other factors may in contrast lead to increased complexity, i.e.…”

Intra- and inter-individual changes in little penguin diving and isotopic composition over the breeding season

“…As such, it is unlikely that little penguin predation alone would deplete its prey. Alternatively, the increase of SST during spring and summer and the associated enhanced stratification of the water column, which lead little penguins to dive shallower and more frequently (Meyer et al 2020) could further explain the decreasing trend of depth use index along the breeding season.…”