DOI: 10.5061/dryad.7sqv9s4x8
title: Acceleration and depth data on foraging behaviour of rhinoceros auklets breeding at Teuri Island

description: Marine top predators are expected to adjust their foraging behaviour at
 multiple time scales concomitantly with changes in forage fish
 availability. Rhinoceros auklets Cerorhinca monocerata rearing chicks at
 Teuri Island, Japan Sea, fed on anchovy Engraulis japonicus in 2012 and
 2013 (anchovy regime) but switched to sand lance Ammodytes spp in 2019 and
 2020 (sand lance regime). Here, we studied their at-sea behaviour using
 the GPS locations of 33 birds and the depth-acceleration records of 26
 birds, and compared their foraging behaviour between these prey regimes.
 At the trip scale, auklets used offshore waters (&gt;50 m sea depth)
 and coastal waters in the anchovy regime but used mainland coastal waters
 (&lt;50 m sea depth) in the sand lance regime. In the sand lance
 regime, the birds also conducted more overnight 2- to 4-day trips in 2020
 and spent more time flying during 1-day trips as they fed in further areas
 compared to the anchovy regime. At the dive scale, auklets frequently dove
 to both &lt;5 m and 20 – 30 m depths in the anchovy regime but mainly
 to &lt;5 m depth in the sand lance regime. Within each dive, auklets
 showed a greater number of fast/strong wing stroke events in the anchovy
 regime than in the sand lance regime. These changes in auklet behaviour
 reflected the different habitats, depth distribution, and swim speed of
 the targeted prey species. Our study shows the behavioural flexibility of
 a wing-propelled flying-diving seabird in response to the inter-annual
 shifts in the dominant forage fish community. It also indicates the
 ecological constraints on the mechanisms determining nest productivity in
 this day-foraging/night-provisioning seabird.
description: We deployed the depth-acceleration data-logger (ORI400-D3GT, 9.0
 g, 12 mm diameter×51 mm, Little Leonardo, Japan) on the back of 
 Rhinoceros Auklets rearing chicks at Teuri Island. The sampling interval
 was 1 second for depth and  0.02 s (50 Hz) or 0.05 s (20 Hz) for 3-axis
 acceleration; sway (X, left-right), surge (Y, tail-head), and heave (Z,
 dorso-ventral). We retrieved depth-acceleration loggers from 8 of 8 birds
 in 2012, 8 of 8 birds in 2013, 10 of 11 birds in 2019, and 8 of 8 birds in
 2020. Because of malfunction or battery shortage in some devices, we
 finally collected depth-acceleration data from 26 birds. Here are the Igor
 files. You can see data and calculation processes using Igor
 software. We defined dives as depth greater than 1m
 considering the accuracy of the depth sensor (0.5m), “dive duration” as
 the time between the previous time the bird first attained 1 m and the
 following time it last attained 1m, “dive depth” as the maximum depth
 during each dive, and “surface time” as the time between the end of dives
 to the start of the next dives. We defined “descent” phase as the time
 from the start of the dives to the time when birds attained 80% of dive
 depth, “ascent” phase as the time between the last time when birds
 attained 80% of maximum dive depth and the end of dive, and “bottom” phase
 as time from the end of descent phase to the start of ascent phase as in
 Kuroki et al. (2003). Rhinoceros Auklets often make “rotations” where they
 switch from ascent to descent and from descent to ascent with a depth
 change rate of greater than 0.5 m s<sup>-1</sup> (Kuroki et
 al. 2003). We typed dives with dive depth &lt; 5 m as “shallow-type”,
 those &gt; 5 m, with no rotation and proportional
 bottom time smaller than 50% of dive duration as “V-type”, and those
 deeper than 5 m, with no rotation and the proportion of bottom time
 greater than 50% as “U-type” referring to Lescroël and Bost (2005), Pütz
 and Cherel (2005), and Halsey et al. (2007). Dives
 &gt; 5 m and with these rotations were typed as
 “W-type”.  During the descent phase, breath hold divers
 are expected to regulate body angle and depth change rate to maximize the
 proportion of foraging time at foraging depths by minimizing the transit
 time but also may search for prey (Wilson et al. 1996). To characterize
 the behaviour during descent, we measured body angle, descent rate (depth
 change per second), and wing stroke frequency (number of wing strokes per
 second, see next section) using depth and acceleration data. The body
 acceleration reflects both slow changes in the body angle and the
 dynamic/fast movement of the body (Yoda et al. 2001). Low frequency
 component of the acceleration was separated by low pass filer using
 Ethographer (Sakamoto et al. 2009) on IGOR Pro ver. 8.03 (WaveMetrics,
 Lake Oswego, USA). As the attachment position of acceleration data-logger
 varied among individuals, we set the critical frequency of low pass filter
 for each bird. The mean values of the critical frequency were 2.2 ± 0.6 Hz
 for tail-head (surge, Y) and 1.8 ± 0.8 Hz for dorso-ventral (heave, Z)
 accelerations. The fast component was derived by subtracting the low
 frequency component.  Body angle (θ) was calculated
 from the low frequency component of surge (YL, Fig. 2 a, b) as arcsinYL
 and incorporating attachment angle of each bird that was the body angle
 when the birds were sitting on the water (Watanuki et al. 2003). We
 compared descent body angle, descent rate, and swim speed at the 1
 s-window closest to 5 m and 10 m depths between prey regimes. The body
 angle of &gt;90° was assumed to be 90°. 1-s windows with the body
 angle of &lt; 0° (7.7% and 7.2% of all windows for 5 m and 10 m depths
 respectively) were excluded from the analyses as these could be
 measurement errors. As the angle of trajectory was almost the same as the
 body angle when Rhinoceros Auklets are descending (Watanuki et al. 2006),
 swim speed can be estimated as r/sin θ where r was the descent rate (m
 s-1). Speed values faster than 2.5 m s<sup>-1 </sup>were
 unreliable (Watanuki and Sato 2008) and excluded from the analyses (3.5%
 and 3.6% of windows with speed data for 5 m and 10 m depths,
 respectively). Dynamic component of the heave (dorso-ventral, Z)
 acceleration reflects up-down body movement in association with wing
 stroke. The number of local minimum of the dynamic component of heave
 acceleration (Fig. 2 c inserted) in each 1-s window was defined as “wing
 stroke frequency”. The maximum amplitude of dynamic component of heave in
 each 1-s window was measured using IGOR (Fig. 2c). Rhinoceros Auklets
 stroked wings by 2-3 Hz while they were cruising in the descent phase
 (Watanuki and Sato 2008, see Fig. 2c).  Wing-propelled seabirds often
 stroke wings fast during dives and these are assumed to relate to the prey
 chase (Ropert-Coudert et al. 2006). We categorize 1-s windows with stroke
 frequencies greater than 4 Hz (mean + 2 * SD of the frequency in 1-s
 window excluding those with no stroke, Supplementary Material 3a) and the
 maximum stroke amplitude greater than 1.04 <em>g </em>(mean +
 2 * SD of the maximum amplitude in 1-s window excluding those with 0
 amplitude) as “fast/strong stroke windows”, then we defined a series of
 the fast/strong stroke windows as “fast/strong stroke event” (Fig. 2d, e).
 The fast/strong wing stroke events at the start of descent could be
 acceleration phase to approach against buoyancy to the prey aggregation.
  In effect, we observed fast/strong stroke events in the descent phase
 mostly at the start of dives (&lt;2 m depth) (Supplementary Material
 4a). In Rhinoceros Auklets, the quick change of the depth (one of the
 indicators of prey chase) was observed mainly in the bottom and ascent
 phases (Kuroki et al. 2003) and the attack scars on the prey fish brought
 back to the chicks are mostly observed underside of the fish (Burger et
 al. 1993); indicating that they possibly chase individual prey in
 bottom/ascent phases. The occurrence of fast/strong wing strokes during
 the descent (Supplementary Material 4a) and the bottom/ascent phases
 (Supplementary Material 4bc), therefore, were analyzed separately. Maximum
 amplitude in 1-s window can be biased to be lower for acceleration sampled
 at longer intervals. To check this potential bias, we put sampling
 frequency (high, 0.02 s interval or low, 0.05 s interval) as potential
 explanatory factor when we analyzed the effects of regime on the duration
 and frequency of fast/strong stroke events.
description:  IGOR Pro ver. 8.03
 (WaveMetrics, Lake Oswego, USA) for the .pxp files. Txt files are provided
 for accessibility.
description: # Acceleration and depth data on foraging behaviour of rhinoceros auklets
 breeding at Teuri Island [Access this dataset on
 Dryad](https://doi.org/10.5061/dryad.7sqv9s4x8∴) Bird List and time of
 start recording data for each logger is in D3GTStartTime Excel file. See
 Supplementary Material 1 for detailed information for each bird. ##
 Description of the data and file structure We deployed the
 depth-acceleration data-logger (ORI400-D3GT, 9.0 g, 12 mm diameter×51 mm,
 Little Leonardo, Japan) on the back of  Rhinoceros Auklets rearing chicks
 at Teuri Island. Igor files for Depth, temperature and 3-axis acceleration
 data collected by D3GT logger deployed on Rhinoceros Auklets at Teuri
 Island. File name is Year_data-logger_sampling interval and Bird ID.
 Sampling interval was 1 second for depth (Depth) and in interval of 0.02 s
 or 0.05 s for 3-axis acceleration; sway (XW, left-right), surge (YW,
 tail-head), and heave (ZW, dorso-ventral). We retrieved depth-acceleration
 loggers from 8 of 8 birds in 2012, 8 of 8 birds in 2013, 10 of 11 birds in
 2019, and 8 of 8 birds in 2020. Because of malfunction or battery shortage
 in some devices we finally collected depth-acceleration data from 26
 birds. Here are Igor files. You can see data and calculation processes
 using Igor software. * XW: X-axis acceleration (sway) * XW_psd: power
 spectrum density of X * ZW: Z-axis acceleration (heave) 　 * ZW_psd: power
 spectrum density of Z * YW: Y-axis acceleration (surge) * YW_psd: power
 spectrum density of Y * DynamicXW: High frequency component of X
 acceleration * DynamicYW: High frequency component of Y acceleration　 *
 DynamicZW: High frequency component of Z acceleration　 * filteredXW: Low
 frequency component of X acceleration　 * filteredYW: Low frequency
 component of Y acceleration　 * filteredZW: Low frequency component of Z
 acceleration * Coef: Coefficient relating to filter　 * modifiedPitch: Body
 angle corrected by the angle of attachment of loggers that was obtained by
 eye for each bird referring the angle when birds were sitting on the
 water. * Pitch: Pitch angle calculated using filteredYW(surge) *
 PitchDetection: The point when modifiedPitch was changed from positive to
 negative * PrePitch: When filterdYW≧ 1　=１，&lt;-1=-1”for calculating Pitch
 * DownStrokeWingbeat: Top convex part of curve of heave (down stroke,
 PreWingbeat2) but higher than threshold determined by eye to determine the
 peak for each bird, during dives. * PreWingbeat: Down convex part of curve
 of heave (up stroke), during dives． * PreWingbeat2: Top convex part of
 curve of heave (down stroke), during dives * Wingbeat: Down convex part of
 heave (up stroke, PreWingbeat) but lower than the threshold determined by
 eye to determine the peak for each bird, during dives. * WingBeatCount:
 The number of Wingbeat (up stroke) per 1-s window, during dives *
 WingbeatHist: Histogram of Wingbeatcount * WingbeatTable: Table of
 Wingbeatcount * BeatConverted: Not used * FlightMask(temporal): Not used *
 FlightMask(2) : Mask of time fly * FlightPreWingbeat: Down convex part of
 curve of heave(up stroke) but lower than the threshold determined by eye
 for each bird, throughout the record　 * FlightWingbeatCount: Number of
 FlightPreWingbeat over the threshold determined by eye for each bird per 1
 second window. Note that WingbeatCount is for time under water but
 FlightWingbeatCount is for throughout the record　． * FrequencyAverage:
 FlightWingbeatCount averaged for 5 second, throughout the record　 *
 MaxAmplitude: Maximum Amplitude of DynamicZW for each 1-s window *
 Amplitude Mask: Mask for time when Amplitude of DynamicZW&gt;1.04 *
 Amplitude 1.04: 1-s time windows when Amplitude of DynamicZW &gt;1.04(0/1)
 * Amplitude 1.32: 1-s time windowswhen Amplitude of DynamicZW
 &gt;1.32(0/1) * overG =1.04: The threshold of maximum amplitude to define
 dash * overHz =4: The threshold of WingbeatCount to define dash * over4:
 Mask for time when wing beat frequency was greater than 4 * over4Asc: Mask
 for time over4 and ascent phase（”DivePhase1”=4） * over4Bot: Mask for time
 over4 and bottom phase（”DivePhase1”=2 or 3） * over4Des: Mask for time
 over4 and descent phase（”DivePhase1”=1） * over4PointAsc: over4Asc points
 on depth wave (１-s）to shown events of 1-s window with wing beat frequency
 greater than 4/s * over4PointBot: over4Bot points on depth wave (１-s）to
 shown events of 1-s window with wing beat frequency greater than 4/s *
 over4PointDes: over4Des points on depth wave (１-s）to shown events of 1-s
 window with wing beat frequency greater than 4/s * Dash: Mask for time 1-s
 windows when amplitude&gt;1.04 and wing stroke frequency&gt;4Hz *
 DashTable; Table for calculation of Dash * DashWave: Not used *
 DconvertedYW: Not used * Dconverted50: Depth at each point giving
 acceleration (sampled at 50 Hz or 20 Hz), using average depth change rate
 at 50 Hz or 20 Hz/ * Pursuit: Mask of time dash in bottom or ascent phase
 * PursuitTable: Table for dash * PursuitWave: Dash event on depth wave
 (1-s) to show when dash occurred during the dive * VeDBA: VeDBA of
 DymanicXW, YW, ZW at 20 or 50 Hz　 * averageVeDBA: average VeDBA in 1-s
 window * AscentMask: Mask for time when depth change rate (/second) was
 negative * AscentPhase1: 80% of maximum depth of a dive to the surface *
 AtoD : Mask for time of　「AtoDChangePoint」（0/1） * AtoDChangePoint: the
 point when change ascent (depth change rate was negative) to descent(depth
 change rate was positive) * BottomAscent: Not used * BottomDurationTable:
 Table for calculating the duration of bottom phase * BottomPhase1: Mast
 for time bottom phase * ChangeDirection: The points when birds changed
 direction from descent to ascent or ascent to descent, excluding points of
 the maximum depth * ChangeDirectionCount: The number of the points when
 birds change direction for each dive deeper than 5 m *
 ChangeDirectionPoint: 1-s windows when there were ChangeDirections (0/1) *
 ChangeDirection5m: The points when birds changed direction from descent to
 ascent or ascent to descent, excluding points of the maximum depth for
 dives deeper than 5 m * Depth: Raw depth data (1-s) * D1: 0/1, Depth ≧ 1 m
 =1, &lt;1 m =0 * D: Corrected depth * DepthChange: Depth change rate（m/s）
 * DescentMask: Mask for time when DepthChange was positive *
 DescentPhase1: Mask for descent phase * Dive: Table for calculating dive
 parameter * DiveID: ID of dives * DiveMask: Mask for time diving *
 DivePhase1: Phase (１ for decent，2 for DeepBottomdepth bottom phase deeper
 than 80% of maximum depth, 3 for ShallowBottom, bottom phase but shallower
 than 80% of maximum depth, 4 for ascent）, 2+3 = bottom phase *
 DiveShapeTable: Table for the number of ShallowBottom per dive *
 DtoAChangePoint: The point when bird changed direction from descent to
 ascent (positive to negative descent rate)　 * ShallowBottom:
 ShallowBottom(DivePhase1=”3”) for calculating DiveShapeTable *
 PhaseChangeTable: Table showing start and end time of bottom phase for
 each dive * PhaseDurationTable: Table showing duration of each phase *
 PreChangeDirection: The points of the change from descent to ascent or
 ascent to descent for making ChangeDirection * Sur: Surface time * Sur1:
 Not used * Sur2: Not used * Temp: Temperature (1-s) * Undulation:
 ChangeDirection but excluding those ChangeDirection occurred in the
 previous 3 seconds．Not used． * UndulationPoint: Mask for time
 with　Undulation * ParameterAt5mTable: Table showing body angle, wing
 stroke frequency and depth change rate at 5 m depth. *
 ParameterAt10mTable: Table showing body angle, wing stroke frequency and
 depth change rate at 10 m depth. * Point5mTable: Table showing points
 (time ) nearest to 5 m for calculating ParameterAt5mTable. *
 Point10mTable: Table showing points (time ) nearest to 10 m for
 calculating ParameterAt10mTable.