DOI: 10.5061/dryad.fbg79cnrz
title: Temporal and spatial differences in the post-breeding behaviour of a ubiquitous Southern Hemisphere seabird, the common diving petrel

description: The non-breeding period plays a major role in seabird survival and
 population dynamics. However, our understanding of the migratory
 behaviour, moulting and feeding strategies of non-breeding seabirds is
 still very limited, especially for small-sized species. The present study
 investigated the post-breeding behaviour of three distant populations
 (Kerguelen Archipelago, south-eastern Australia, New Zealand) of the
 common diving petrel (Pelecanoides urinatrix), an abundant, widely
 distributed zooplanktivorous seabird breeding throughout the southern
 Atlantic, Indian and Pacific oceans. The timing, geographical destination
 and activity pattern of birds were quantified through geolocator
 deployments during the post-breeding migration, while moult pattern of
 body feathers was investigated using stable isotope analysis. Despite the
 high energetic cost of flapping flight, all the individuals quickly
 travelled long distances (&gt; ~2500 km) after the end of the breeding
 season, targeting oceanic frontal systems. The three populations, however,
 clearly diverged spatially (migration pathways and destinations), and
 temporally (timing and duration) in their post-breeding movements, as well
 as in their period of moult. Philopatry to distantly separated breeding
 grounds, different breeding phenologies, and distinct post-breeding
 destinations suggest that the common diving petrel populations have a high
 potential for isolation, and hence, speciation. These results contribute
 to improving knowledge of ecological divergence and evolution between
 populations and inform the challenges of conserving migratory species.
description: <b>Methods
 </b> <i>Study site, study
 species and animal instrumentation</i> The study was conducted at three
 field sites representing separate populations: Ile Mayes (Kerguelen
 Archipelago, southern Indian Ocean, 49°28’S 69°57’E, hereafter referred as
 Kerguelen); Kanowna Island (south-eastern Australia, 39°10’S 148°16’E);
 and Mana Island (New Zealand, 41°06’S 174°46’E). In order to avoid
 potential bias due to inter-annual variations, individuals from all three
 colonies were sampled during the same non-breeding period (November 2017
 to September 2018). Additional data was collected for Kerguelen (in
 2015-16 and 2016-17) and Kanowna Island (in 2016-17 and 2018-19).
 Kerguelen is located in subantarctic waters <i>sensu lato</i>
 (between the Polar Front and the Subtropical Front), while both Kanowna
 and Mana Islands are located farther north, in the temperate subtropical
 region. In the
 present article, migration is defined as the period during which there is
 an annual to-and-from movement of populations between the breeding site
 and a migration area [1]. The post-breeding period is defined as the
 period between the last burrow attendance at the end of the breeding
 season, and the first return in a burrow the following season. The
 non-breeding period is the period between two successive breeding cycles.
 It includes the post-breeding migration away from breeding sites, followed
 by a more or less prolonged period in the vicinity of breeding sites
 before initiating the next breeding season.   To study the at-sea distribution of
 individuals from the three populations during the non-breeding period,
 adult birds were equipped with leg-mounted GLS (Migrate technology, model
 C65). The mass of the device attached to a plastic or metal ring with a
 cable tie was &lt; 1.5 g, corresponding to on average 1.07 ± 0.1% of
 body mass (117 g – 175 g). Previous use of such devices on small seabird
 species have shown limited impact on the feeding ecology or future
 breeding [27, 41]. Breeding individuals were equipped at the end of the
 breeding season and were recaptured during the following breeding season
 for removal of the device. Sex was determined by DNA analysis of a small
 blood sample (0.1 mL) collected from the brachial vein for the individuals
 from Kerguelen (Laboratoire Analyses Biologiques, CEBC, France), and of a
 body feather for those from Kanowna Island (DNA solutions, Australia). The
 sex of individuals at Mana Island was determined from their sex-specific
 calls [5, 42].   Information on moult pattern in
 Pelecanoididae species is very limited, largely because individuals can be
 at sea during this stage [5]. Similarly to alcids, the majority of diving
 petrel species seem to undergo an annual almost synchronous wing molt of
 flight feathers during the non-breeding period [44, 45]. For CDP, in
 south-eastern Australia and New Zealand, adults are thought to start wing
 moult at sea after chicks have fledged [5]. In South Georgia, Kerguelen
 and Heard Island, moult of primaries seems to be initiated just before the
 end of the chick-rearing period [5, 43], although sources are discordant
 [46]. However, the accuracy of these records is complicated by the lack of
 information on the breeding status of the observed individuals. In the
 present study, the timing of wing moult was inferred from information
 provided by the GLS on the time spent on the sea surface. Since flight
 feather renewal directly affects flying ability [45, 47, 48], in
 particular for species with high wing loading (body mass / wing area) such
 as diving petrels [49], a peak in time spent on the water is likely to
 reflect the wing moult of flight feathers.   For body feathers, it is likely to
 be a protracted process initiated during the post-breeding period,
 similarly to other species of small petrels [50, 51]. The continuous moult
 of body feathers throughout the non-breeding period allows the birds to
 progressively renew their plumage while maintaining its vital role in
 thermoregulation [52]. Stable isotope ratios in body feathers can be a
 proxy of the location and trophic level of the individuals when they were
 synthetised [19, 20]. Therefore, to investigate the isotopic niche and the
 moult of body feathers of individuals throughout the non-breeding period,
 four contour feathers were collected from the middle and lower back of
 each tracked individual at recapture. Additional samples were collected on
 adult individuals that were not tracked in order to increase the sample
 size and to assess temporal variation (three years of data for both
 Kerguelen and Kanowna). Handling time at deployment (measurements, banding
 and GLS attachment) and recapture (device removal, weighing, blood and
 feather sampling) were minimized and took on average &lt; 5
 min.  
 <i>Data processing and
 analyses</i> The GLS measured light intensity
 every minute and recorded the maximum value for each 5 min interval. The
 determination of twilights (dawn and dusk), linked to a time base, enabled
 longitude (timing of local midday and midnight) and latitude (duration of
 day and night) to be estimated, providing two positions per day with an
 average of 186 ± 114 km (mean error ± SD; [53]). Processing and
 calculations were conducted using the <i>GeoLight </i>package
 in the R statistical environment [54, 55]. As latitude estimations around
 the equinoxes are unreliable, data for two weeks before and after the
 equinoxes were excluded before spatial analysis was conducted [56].
 Additionally, latitude or longitude estimates that were clearly inaccurate
 (unrealistic speed &gt; 1500 km/day, trajectory or spikes) were
 removed [31]. When outward and inward movements were occurring during the
 equinox periods (March-April and September-October), the timing of arrival
 and departure from the breeding colonies was determined from longitudinal
 directional movements using the raw data [31, 48].   Filtered locations were used to
 generate kernel utilization distribution (UD) estimates with a smoothing
 parameter (<i>h</i>) of 1.8 (corresponding to a search radius
 of ~ 200 km) and 1º x 1º grid cell size (based on the mean accuracy of the
 device). For each population and year, the 50% (core foraging area) and
 95% (home range) kernel UD contours were obtained [57]. The core area was
 used to estimate the centroid position (mean latitude and longitude)
 during the post-breeding period for each individual. Spatial analyses were
 performed using the <i>adehabitatHR</i> R package
 [58].  
 The period of maximum
 proportion of time spent on the water (wet-dry sensor being wet &gt;
 90% per day; [35]) was used to determine the moulting period of flight
 feathers for each individual [48]. This was recorded differently at the
 three study sites. For Kerguelen and Kanowna Island, wet-dry data were
 sampled every 30 s with the number of samples wet and maximum conductivity
 recorded every 4 h. At Mana Island, wet-dry data were sampled every 30 s
 with number of wet samples and maximum conductivity recorded every 10
 min. The dates of
 last and first burrow attendance were determined by combining information
 on activity (wet-dry: 100% dry for a period &gt; 4 h), temperature
 (for Kerguelen and Kanowna Island only, sampled every 5 min with maximum
 recorded every 4 h) and movement data (presence of the bird in the
 vicinity of the breeding region). These data were then used to estimate
 the duration and the total distance travelled during the post-breeding
 migration.   For stable isotope analyses,
 feathers were cleaned of surface lipids and contaminants using a 2:1
 chloroform:methanol solution in a ultrasonic bath, followed by two
 successive methanol rinses and air dried 24 h at 50°C. Each feather was
 then cut to produce a fine powder for homogenization before carbon and
 nitrogen isotope ratio determination using a continuous flow mass
 spectrometer (Delta V Plus or Delta V Advantage both with a Conflo IV
 interface, Thermo Scientific, Bremen, Germany) coupled to an elemental
 analyser (Flash 2000 or Flash EA 1112, Thermo Scientific, Milan, Italy) at
 the LIENSs laboratory (La Rochelle Université, France). Stable isotope
 values were expressed in conventional notation (<i>δX</i> =
 [(<i>R</i><sub>sample</sub>/<i>R</i><sub>standard</sub>) – 1]) where X is <sup>13</sup>C or<i> </i><sup>15</sup>N and R represent the corresponding ratio <sup>15</sup>N/<sup>14</sup>N or <sup>13</sup>C/<sup>12</sup>C. <i>R</i><sub>standard </sub>values were based on Vienna Pee Dee Belemnite for <sup>13</sup>C, and atmospheric nitrogen (N<sub>2</sub>) for <sup>15</sup>N. Replicates of internal laboratory standards (Caffeine USGS-61 and USGS-62) indicate measurement errors &lt; 0.10 ‰ for <i>δ</i><sup>13</sup>C and 0.15 ‰ for <i>δ</i><sup>15</sup>N. As the Southern Ocean is marked by a latitudinal gradient of <i>δ</i><sup>13</sup>C and <i>δ</i><sup>15</sup>N (Jaeger et al. 2010), low (<i>δ</i><sup>13</sup>C &lt; -19.5 ‰ and <i>δ</i><sup>15</sup>N &lt; 9.9 ‰) and high isotopic values (<i>δ</i><sup>13</sup>C &gt; -19.5 ‰ and <i>δ</i><sup>15</sup>N &gt; 9.9 ‰) in body feathers were interpreted as corresponding to feathers moulted in Antarctic/Subantarctic and Subtropical/neritic waters, respectively [36, 59].   All spatial and statistical analyses were conducted in the R statistical environment 3.6.1 [55]. To investigate among-population, inter-annual and sex-related variations on post-breeding migration parameters (departure and return dates, migration duration, total distance travelled and maximum range), general linear models (GLM) were fitted using the <i>lme4</i> package [60]. For all models a Gaussian family was selected (error structure approached the normal distribution), all combinations of variables were then tested and ranked based on their Akaike’s Information Criterion (AIC), and the global models were checked to ensure normality and homoscedasticity of the residuals [61] before further statistical tests. Inter-population differences were quantified using analyses of variance (ANOVA or Welch’s ANOVA), and <i>post-hoc</i> tests were conducted using <i>t</i>-tests (parametric), or Kruskal-Wallis and Mann-Whitney <i>U</i> tests (non-parametric) depending on the data distributions. Before these analyses, data were checked for normality (Shapiro-Wilk test) and equality of variances (Levene test). Estimates are presented as means ± standard error (unless specified).