What Is A Penguins Defensive Action (Animal)
R Soc Open Sci. 2018 Aug; 5(viii): 171449.
Behaviourally mediated predation abstention in penguin casualty: in situ show from animal-borne camera loggers
Jonathan M. Handley
aneDST/NRF Centre of Excellence at the FitzPatrick Institute of African Ornithology, Department of Zoology, Nelson Mandela Academy, South Campus, Port Elizabeth 6031, S Africa
Andréa Thiebault
oneDST/NRF Centre of Excellence at the FitzPatrick Constitute of African Ornithology, Department of Zoology, Nelson Mandela University, Southward Campus, Port Elizabeth 6031, South Africa
Andrew Stanworth
twoFalklands Conservation, PO Box 26, Stanley FIQQ 1ZZ, Falkland Islands
David Schutt
3Department of Integrative Biology, University of Colorado Denver, PO Box 173364, Denver, CO 80217, U.s.
Pierre Pistorius
iDST/NRF Centre of Excellence at the FitzPatrick Institute of African Ornithology, Section of Zoology, Nelson Mandela University, South Campus, Port Elizabeth 6031, South Africa
Received 2017 Sep 23; Accepted 2018 Jul 19.
- Information Citations
-
- Handley J, Thiebault A, Stanworth A, Schutt D, Pistorius P. 2018. Data from: Behaviourally mediated predation abstention in penguin prey: in situ evidence from animal-borne photographic camera loggers Dryad Digital Repository . ( ten.5061/dryad.5247q) [CrossRef]
- Supplementary Materials
-
Instructions for supplementary data and video captions
GUID: 9A5DA582-570E-41C1-8FF7-38C7F9993A2E
Additional method details, and solutions for video assay
GUID: C3259AE4-146E-4AFE-A501-31D50DD467EB
Behavioural Category Descriptors
GUID: 581B9AFD-6C20-4762-A4F9-B99EC3A59A5E
- Data Availability Statement
-
Raw information and boosted information uploaded as the electronic supplementary cloth and in Dryad repository (http://dx.doi.org/10.5061/dryad.5247q) [31].
Abstract
Predator dietary studies often assume that nutrition is reflective of the diverseness and relative abundance of their casualty. This interpretation ignores species-specific behavioural adaptations in prey that could influence prey capture. Here, we develop and describe a scalable biologging protocol, using animal-borne camera loggers, to elucidate the factors influencing casualty capture by a seabird, the gentoo penguin (Pygoscelis papua). From the video prove, we prove, to our knowledge for the first time, that ambitious behavioural defence mechanisms by prey can deter casualty capture by a seabird. Furthermore, we provide prove demonstrating that these birds, which were observed hunting solitarily, target prey when they are nearly discernible. Specifically, birds targeted casualty primarily while ascending and when casualty were not tightly clustered. In decision, nosotros evidence that prey behaviour can significantly influence trophic coupling in marine systems because despite prey being nowadays, information technology is not always targeted. Thus, these predator–prey relationships should exist accounted for in studies using marine top predators as samplers of mid- to lower trophic-level species.
Keywords: seabird, penguin, creature-borne photographic camera, predator–prey, confusion effect, indicator species
one. Introduction
Studies in the marine realm which focus on predator–prey relationships [1–three] face the challenge that simultaneous sampling of both higher trophic order predatory species and their prey is often logistically and financially difficult. Thus, a common arroyo is to apply proxies of prey availability, whereby the level of focus on predator–prey relationships relates to usage of various habitat components within the home range (third-order option, [4]). This has been accomplished using technology such as animal-borne tracking devices and either trawls or acoustic monitoring, to investigate predator and casualty distribution, respectively [2,3]. However, while some studies have institute concordance between predator and prey distribution [iii], others accept yielded inconclusive results when relating demographic parameters, distribution and dietary composition of predators to the availability and abundance of prey [two,5,6]. For example, a recent study tracked 2 penguin species (Adélie (Pygoscelis adeliae) and gentoo (Pygoscelis papua) penguins) using Argos satellite tags and fourth dimension-depth recorders, and obtained most real-fourth dimension distribution of prey fields using autonomous underwater vehicles. While krill aggregation information were not available for every penguin dive, investigators were unable to fully determine whether dense or lengthened aggregations of Antarctic krill (Euphausia superba), or species-specific penguin behaviours, drove the observed vertical segregation between penguin species [2]. This means in situ studies which can provide empirical show at the private level, about the bodily procurement of food items from those available at that site (fourth-club selection) [iv], should profoundly heighten our understanding of a predator's foraging ecology.
Intrinsic factors, including variable energetic requirements associated with self-maintenance and reproduction, and extrinsic factors, such as anti-predator behaviour employed by casualty target species, are known to influence prey selection in terrestrial predators [seven,8]. For marine diving predators, such as penguins, there is however limited knowledge regarding how both predator and prey may influence the success of capture [9–12]. Furthermore, penguins accept been accounted sentinels of the marine surround [13], with diverse seabird associated proxies, such equally behavioural and demographic measurements, potentially indicating the land of the marine environment [5,vi,14]. Therefore, there is a pressing demand to improve sympathise behavioural interactions betwixt seabirds and their prey, and the role these upper trophic-level predators might play as samplers of mid to lower trophic-level species.
Understanding predator–prey interactions ideally requires direct observation, which is now viable for penguins owing to advances in animal-borne photographic camera loggers [15]. The characteristics of gentoo penguin foraging behaviour, specifically the fact that they undertake relatively short foraging trips, brand them a well-suited study species for camera deployments. Contempo dietary studies at the Falkland Islands, based on tummy content analysis, found that each bird typically feeds consistently during a trip on the aforementioned prey items at a given colony and during a specific breeding catamenia [16,17]. Furthermore, gentoo penguins are primarily diurnal, inshore foragers, seldom travelling farther than 30 km from their convenance colony [18]. Therefore, while video cameras accept limited recording chapters, the footage obtained should offer valuable insight towards their general foraging behaviours. Thus, the aim of this study was to sympathise fine-scale predator–prey interactions for gentoo penguins at the Falkland Islands, using animal-borne camera loggers. Furthermore, we develop a widely applicable, freeware protocol, scalable across other studies which require detailed annotation and estimation of large quantities of video data.
2. Cloth and methods
We studied gentoo penguin foraging behaviour during the guard period of chick rearing in Dec 2013. 30-eight birds were sampled from 2 colonies at the Falkland Islands, Balderdash Roads (BR) (52.3096° S, 59.3896° W) and Cow Bay (CB) (51.4288° Due south, 57.8703° Due west), each with approximately 1236 and 1821 breeding pairs, respectively [xix] (figure 1). We chose these colonies because birds depart and render from the sea using a single location, and the colonies are over 500 thousand away from the shore line. Therefore, birds could be captured without disturbance at the colony. At both colonies, birds typically depart early in the morning (05.00–07.00) for a foraging trip. The cameras used in the study could tape for up to xc min and began recording from the moment they were switched on. Therefore, developed birds were caught while heading to the sea. We chose birds that had a visible brood patch and signs of sitting on a nest. A key sign was to look for fouled birds as nests were typically built from scrub bush cloth, diddle-dee (Empetrum rubrum), on peaty soil. Furthermore, the shut proximity of birds inside a colony often meant that a nesting individual would be fouled past nearby birds. During instrument deployment, birds were given a unique mark on the breast feathers, to permit for their identification upon return from the sea, using a greenish, temporary, waterproof wax marker (ROTO.STIK, Sheepman Supply Co.). We recaptured birds afterwards a single foraging trip past maintaining a continual lookout of the body of water exit betoken, until 23.00 daily. Upon recapturing, devices were removed, birds were weighed, and pecker length and bill depth recorded. Nosotros after searched for sampled birds in the colony based on their unique mark, allowing us to confirm the breeding status.
Gentoo penguin colonies (black dots) of the Falkland Islands (top panel), including the two study colonies (stars), Bull Roads (BR) and CB Cow Bay (CB). Tracks (n BR = 13, n CB = 9) in blue (eye and bottom console) indicate foraging paths of instrumented birds which had valid GPS data, while yellowish overlays point the period of time while cameras were recording.
The camera deployments occurred equally part of an ongoing study where birds were fitted with a: CEFAS G5 fourth dimension-depth recorder (TDR; CEFAS Technology Ltd, Lowestoft, UK), CatTraQ GPS logger (Catnip Technologies) and custom waterproofed Replay XD 1080 Hd photographic camera (Stable Imaging Solutions, LLC, USA) (electronic supplementary material, figure S1). Devices were set up to record at 1 s intervals, 1 min intervals and 30 frames per 2d, respectively. The cumulative mass of devices was 172.7 grand, accounting for ≈2.7% mass of the instrumented birds and ≈six% of birds' cross-sectional surface surface area. Devices were secured to the birds using overlapping layers of waterproof adhesive TESA® tape (Beiersdorf, AG, GmbH, Hamburg, Frg), with the tape ends sealed using cyanoacrylate gum (Loctite 401®). Securing units this way ensures the feather is left untarnished following device removal.
A standard protocol for the annotation and quantification of video data derived from beast-borne camera loggers does not yet be. Thus, we developed a protocol using freeware. First, nosotros converted video from .MOV to .AVI with MPEG Southtreamclip (5. i.2) [20], then that, secondly, video could be annotated using Solomon Coder (v. 16.06.26) [21]. We recorded eleven main categories of observations (detailed in the electronic supplementary material). Specific to this report are categories that chronicle to prey, and intra- and interspecific interactions. Furthermore, the bird'due south orientation in the water column was recorded, based on concrete features (sea surface/bounding main floor) and the changing light-intensity levels, evident when the bird was ascending or descending. Also, when birds were foraging forth the sea floor, we recorded whether birds used upward or downwardly strikes of the head during attempted prey captures (APC). Information technology was not always feasible to determine if prey were consumed or not. Therefore, nosotros divers an APC as the clearly distinguished moment of a bird actively raising and striking its caput towards the prey item until the moment its head returned to a neutral position, after the bird may have either been successful in capturing the item or not.
Prey size was estimated past comparison information technology to penguin bill size at the moment the prey was side by side to the bill, thus limiting the effect of unknown distance which could confound this measurement. The estimation of casualty size allowed the states to categorize prey both by type and broad size class (e.g. small versus big). When prey were aggregated, we noted whether aggregations were loosely or tightly clustered. Loose aggregations were characterized every bit those which had obvious infinite betwixt prey items and where one could clearly see through the aggregation during the entire menses that the bird was approaching. Tightly aggregated prey were characterized by having no obvious space between prey items and where one could not see through the aggregation during the bird's arroyo. In line with our freeware protocol, we used custom codes in R iii.1.two [22] to determine, from the annotated video files, the recording duration, number of APCs and what orientation birds occurred in, and the number of interactions with conspecifics and heterospecifics. We extracted unique behavioural events (still images) by frame number, using the freeware FFmpeg (v. Northward-82324-g972b358) [23].
Information from TDR and GPS devices were candy every bit part of the ongoing written report, which immune for the visualization of where along the foraging path footage was recorded from. Specifically, information from TDR devices were processed with the 'diveMove' bundle [24]. GPS data were outset filtered for erroneous locations using the speedfilter office ('trip' package, [25]), based on the algorithm past McConnell et al. [26], when the average transit speed between them was greater than viii km h−1 [27]. Furthermore, the diving nature of penguins results in intermittent positional fixes. Therefore, the filtered data were candy using a continuous-time correlated random walk model (implemented in the 'crawl' package, [28]) to generate the most probable path used by a bird, through simulation of 100 possible tracks. The filtered data were matched to the photographic camera annotations using the 'interp1' role of the 'bespeak' package [29]. Equally data from the three devices were prone to clock drift, data were visually aligned using the Ethographer extension in IGOR Pro (WaveMetrics, Inc.) [30].
Data are presented equally mean and standard deviation, unless stated otherwise. The electronic supplementary textile provides the camera annotations and R script from the report [31]. Furthermore, nosotros likewise provide a stepwise example of software employ, example data files and custom R script, which also shows how to merge data from multiple tags.
3. Results
We obtained suitable footage from 14 and 17 birds at BR and CB, respectively, yielding a total of 35.six h of footage which was recorded from the starting time of foraging trips (figure one). In the remaining cases, three birds were not recaptured despite a week of continuous observation for birds post-deployment. Thus, nosotros doubtable these to accept been not-breeders as gentoo penguins guarding chicks rarely provender over multiple days before returning to the nest [eighteen]. The other four birds were recaptured, only but entered the water after the cameras had ceased recording. On average, the first 69 (±12.6) min of a trip were recorded and all birds, apart from 1, had APCs within the video recording.
APCs involved foraging on vii unlike casualty types, with an boilerplate of 52 (0–284, median/range) and a full of 1932 individual APCs being identified for each bird and across all birds, respectively (electronic supplementary material, movie S1, shows examples of each prey type observed during APCs). The seven types of prey involved in the APCs included lobster krill (n = 599, Munida spp.), small fishes (northward = 375, probably juvenile stone cod, either Patagonotothen tessellata or Patagonotothen ramsayi, less than 30–40 mm fish standard length (tip of the snout to posterior end of the last vertebra)), larger fishes (n = four, unidentified, greater than 70 mm fish standard length) and developed squid species (northward = four, probably Patagonian squid (Doryteuthis gahi)). We as well observed 78 APCs on two unidentifiable items (item 1, n = 27; item 2, north = 51) and 872 APCs where birds showed the feature head-striking movement of an APC, but no casualty particular could be observed. Information technology is probable that the bulk of these 872 APCs were as well for minor fishes or maybe, just less probably, the amphipod, Themisto gaudichaudii, based on previous dietary studies in the region [16] and the similar feature in head strike movement when modest fishes were definitively observed (J. Chiliad. Handley 2014, personal observation).
Birds did non appear to pursue either lobster krill or small fishes and swam in a uniform manner using quick strikes of the caput to capture prey which were nowadays within their trajectory. When birds clearly missed these casualty items (north = 109), they did not appear to deviate from their course and continued swimming uniformly. This contrasted with the larger squid and fishes, where it was clear that birds pursued prey. Notwithstanding, these larger items were seldom encountered (n = 8).
Based on the orientation of birds evident in the camera footage, birds primarily fed while ascending, followed nearly as past feeding in the water cavalcade where orientation was unclear (pelagic foraging) or with upward strikes of the head while foraging along the body of water floor (table 1). Furthermore, for the lobster krill, there were relatively few APCs while foraging along the sea floor (northward = 9), despite clear evidence in 64 split events where lobster krill were present on the sea flooring. An event was considered from the moment a bird began swimming over a section of body of water flooring containing lobster krill, until the section concluded, and each lasted an average of ii.3 due south (0.17–31.4 s, median/range) (electronic supplementary textile, film S1). Rather, APCs on lobster krill occurred primarily by birds attacking unmarried individuals while ascending or foraging pelagically (table 1).
Tabular array one.
Orientation of gentoo penguins while feeding on all prey and the two master prey types observed, lobster krill (Munida spp.) and small fishes (probably Patagonothen spp.). (Total number of attempted prey captures (APCs) and percent are shown.)
| penguin orientation | all prey items (%) | lobster krill (%) | small fishes (%) |
|---|---|---|---|
| surface (stationary) | 0 (0) | 0 (0) | 0 (0) |
| surface (swimming below) | 1 (0.1) | 0 (0) | 0 (0) |
| descend | 26 (1.3) | 5 (0.8) | 5 (1.iii) |
| body of water floor (caput downwards) | 65 (3.4) | 9 (1.5) | 4 (1.ane) |
| body of water floor (caput up) | 479 (24.8) | 4 (0.7) | 107 (28.v) |
| pelagic | 525 (27.2) | 182 (30.4) | 86 (22.9) |
| ascend | 836 (43.3) | 399 (66.vi) | 173 (46.1) |
| total | 1932 (100) | 599 (100) | 375 (100) |
In that location were 29 events, involving 10 different birds, where we observed private lobster krill avoiding capture by actively defending themselves with their pincers (figure ii; electronic supplementary material, picture S2). Five birds also encountered lobster krill swarms (northward = 44) during their foraging trip. Sixteen of these swarms looked to be loosely aggregated, and in these instances birds fed from the periphery. One bird swam directly into a loosely aggregated swarm and captured lobster krill. However, for the other 28 swarms, in which lobster krill appeared tightly amassed, birds headed towards them simply did not feed off the swarms (effigy three; electronic supplementary material, picture S3).
Lobster krill Munida spp. (a) Defensive position—pincers open—every bit the bird heads towards it. (b) Lobster krill is attacking the bird with pincers during an attempted prey capture (APC). In both these instances, birds were unsuccessful in capturing the lobster krill.
Gentoo penguins were observed to feed off (a) loosely amassed swarms of lobster krill (n = 16); however, the birds did non feed off (b) tightly amassed swarms (n = 28).
There was no evidence of birds hunting prey cooperatively (e.g. more than one penguin foraging on the same prey patch), every bit birds from both colonies had negligible interactions (pct of trip time), with both conspecifics (BR = 0.43%[0.86], CB = 3.66%[0.86]) and other penguin species (BR = 0%[0], CB = 0.thirteen%[0.17]). When interactions did occur, they appeared to be either chance encounters with the subject bird either ignoring other individuals or following them briefly (electronic supplementary material, movie S4).
four. Discussion
We provide, to our cognition, the first evidence of a reduction in foraging success for penguins owing to two anti-predator tactics used by prey: active defence past individuals, and group formation. This highlights a caution for marine predator studies bold a direct human relationship between relative casualty availability and dietary composition. Thus, equally has often been recognized in terrestrial systems, the context in which prey and predator find themselves must be considered [32,33].
A cardinal consideration in biologging studies is the tag bear upon. For penguins, at that place are mixed results regarding the caste to which birds are affected, either neutrally or negatively [34–36]. Based on current of air tunnel tests looking at drag on diverse species, it is clear that numerous aspects should exist considered when looking at the event of a tag on a diving marine predator, such equally tag cross-sectional expanse, average swimming speed, casualty capture methods and duration of tag deployment [37,38]. Therefore, while we did not measure the effects of tags on the behaviour of the individuals in our study straight, we expect tag effects on the birds, and their prey capture power, to be negligible for the following reasons: (i) the typical casualty capture method by gentoo penguins did non involve birds actively pursuing prey; the same type of casualty readily observed in dietary studies [16]; (2) even when gentoo penguins did actively pursue casualty, we observed them to exist successful in capturing big squid which required pursuit; and (3) tags were only deployed for a unmarried foraging trip, thereby minimizing possible long-term effects on fettle.
The assemblage of lobster krill into swarms appeared to have an impact on whether gentoo penguins captured these prey items or not. Aggregating casualty can reduce susceptibility to predation through attack dilution, increased overall vigilance, communal defense force and predator confusion [8]. Disentangling which 1, or combination, of these mechanisms may bulldoze swarming behaviour in lobster krill is challenging. However, as birds typically targeted private lobster krill or those on the periphery of swarms that were non as tightly amassed, this interaction by penguins to swarms of lobster krill lends support to these predators existence influenced past communal defense and the confusion effect. The confusion effect arises when prey behaviour limits the ability of a predator to single out casualty items from tightly packed groups which present a greater visual bulwark; every bit has been documented for a multifariousness of predators such equally invertebrates, fishes and other birds [39,40]. More than recently, the first in situ observations from African penguins (Spheniscus demersus) reaffirm this, as fish separated from the shoal were virtually likely to exist caught by the birds [11].
Regarding communal defense force, while we could not observe this directly from the video footage, the attacks observed from individual lobster krill mean that it is likely each swarm constitutes multiple lobster krill defending themselves from attack. Therefore, birds must consider the trade-off betwixt the short-term gain in free energy versus the possible long-term reduction in foraging efficiency should the bird become injured. For many species, where individuals have sustained sublethal injuries from prey, these individuals are often limited to catch suboptimal prey with the net consequence being reduced fitness [41]. Conspicuously, the method used past gentoo penguins to capture lobster krill and most prey, which involves attacking private items from below, helps to minimize handling time and capture prey individuals before they tin can orientate themselves into a defensive position. This might further explain why birds seldom attacked lobster krill on the sea floor. These individuals are probably able to defend themselves better given their orientation, and also size, as larger adults typically aggregate on the seabed [42].
To overcome prey defensive power and increase the chance of singling out prey in a school, or swarm, predators often use a cooperative hunting strategy [viii,43,44]. While grouping foraging has been observed by gentoo penguins at Antarctic localities [9,45], the camera footage revealed that this was not the case for gentoo penguins at the Falkland Islands. For other penguin species, variable bear witness suggests that birds may provender individually or cooperatively [9,46,47]. However, even for those species that show cooperative foraging, they may still be more than successful when targeting aggregating casualty lone [10]. This appears to be in contrast to a situation where multispecies assemblages attacking grouped casualty increased the feeding success of each individual [48]. These studies, nevertheless, were non able to consider prey defensive ability. Therefore, our study reinforces that casualty ability to avoid predation, and whether predators forage alone or cooperatively, must be considered when exploring broader facets relating to predator–prey dynamics [v,6,14].
Notably, birds did not deviate from their general swimming management when they missed lobster krill or small fishes. Birds did, yet, actively chase after the eight larger casualty items; which might point that their behaviour is consistent with optimal foraging theory [49,50]. Thus, our anecdotes may indicate that penguins will exert a greater corporeality of free energy when the returns would exist higher. This behaviour, and those discussed above, imply that birds may attend to the specific challenges presented by each prey type. Furthermore, gentoo penguins may proceed track of potential casualty availability within their home range when one considers the 'predator pass-along effect' [7]. This machinery is driven by predator movement as a outcome of unsuccessful attacks, and suggests that a predator might spread the risk over many hunting sites to manage prey behaviour, benefiting the predator'due south long-term energy intake.
While our study highlights a predator–prey interaction for gentoo penguins at merely ane locality, the use of animal-borne camera loggers provided clear testify that where there is readily bachelor prey, this may not necessarily exist targeted by the predator. Hence, while Antarctic krill cannot defend themselves like lobster krill, our study provides insight into why in that location may be a mismatch between predator and casualty distribution observed for gentoo penguins elsewhere [2]. The implications of our study are that considerations such as the power of prey to avoid predation, and the degree to which predator and casualty interact when in relatively close proximity, must be considered when characterizing dynamic marine systems. Thus, caution must exist taken confronting oversimplifying trophic studies involving marine elevation predators because nosotros may arrive at naive conclusions when relating demographic parameters or distribution, as well as dietary composition of predators, to the availability and abundance of prey [5,half dozen,14].
Supplementary Material
Instructions for supplementary information and video captions:
Supplementary Textile
Boosted method details, and solutions for video analysis:
Supplementary Fabric
Behavioural Category Descriptors:
Acknowledgements
Dr Paul Brickle: casualty identification. North Arm Subcontract and Johnsons Harbour (state owners and wardens): provided access to written report colonies and logistical support.
Ethics
Research let: Falkland Islands Environmental Planning Department (R17/2011 and R13/2012). Brute ethics: Nelson Mandela Metropolitan Academy Ethics Commission (ALL-SCI-ZOO-014).
Authors' contributions
J.K.H., A.T. and P.P. conceived the study. J.M.H., D.South., A.S. and P.P. sourced funding. J.M.H., D.S. and A.South. performed fieldwork. J.M.H. and A.T. analysed data. J.G.H wrote the paper with input from all the authors.
Competing interests
Nosotros declare we have no competing interests.
Funding
Grants: Rufford Modest Grants Foundation (grant no. 12372-1), John Cheek Trust, Falkland Islands Environmental Planning Section and Nelson Mandela Metropolitan University Enquiry Capacity Department. Additional stipends: National Enquiry Foundation of S Africa.
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