Kleptoparasitism in foraging gentoo penguins Pygoscelis papua
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An ongoing challenge in marine top predator research is understanding processes that are responsible for patterns that are often derived from land-based access to individuals. The use of animal-borne camera loggers, however, is proving useful in this regard as researchers can directly observe species and habitat-associated interactions. During an ongoing study investigating the foraging ecology of gentoo penguins (Pygoscelis papua) at the Falkland Islands, we observed the first attempted underwater intraspecific kleptoparasitism event for a penguin. This was revealed through a bird deployed with an animal-borne camera logger. Although unsuccessful in its attempt, the new reported behaviour highlights a novel interaction and further demonstrates the value of cameras in better understanding the ecology of marine vertebrates.
KeywordsPygoscelis Penguin Camera Kleptoparasitism
The marine environment presents a unique challenge for observations of an animal’s proximate environment (Tremblay et al. 2014). For penguin species, Ponganis et al. (2000) were the first to address this challenge by utilising an animal-borne camera logger which revealed the sub-ice foraging behaviour in emperor penguins (Aptenodytes forsteri). Since this time, cameras have given insight into social foraging behaviours of chinstrap penguins (Pygoscelis antarctica) (Takahashi et al. 2004) and feeding behaviour of gentoo penguins (Pygoscelis papua) on krill (Takahashi et al. 2008). Additionally, they have been used as environmental samplers for showing the distribution of other marine organisms (Kokubun et al. 2013) and most recently they have allowed for tests of optimal foraging theory in the Adélie penguin (Pygoscelis adeliae) (Watanabe et al. 2014). The current article adds to this growing body of knowledge in animal behaviour within the marine environment. We report on a unique observation showcasing the first attempted intraspecific kleptoparasitism event for a penguin, which was recorded during an on-going study examining the foraging ecology of gentoo penguins at the Falkland Islands.
Kleptoparasitism refers to a form of interference competition between unrelated individuals (Iyengar 2008) and can be defined as the act of stealing a resource already in the host’s possession or for which the host has expended energy and capture by the host is imminent (Brockmann and Barnard 1979; Morand-Ferron et al. 2007; Iyengar 2008). The act usually occurs through one of three ways, (1) aggressive kleptoparasitism, through force or threat, (2) scramble kleptoparasitism, when resources are exploited by two or more individuals after identification by one, and (3) stealth kleptoparasitism, where food is stolen while avoiding host interaction (Giraldeau and Caraco 2000). For non-captive seabirds, this behaviour, with particular respect to food items, has typically been recorded amongst the volant, predatory species (e.g., Brockmann and Barnard 1979; Morand-Ferron et al. 2007; Fulton 2010), but to our knowledge has not been documented for foraging penguins.
The gentoo penguin is a predatory seabird that exhibits a high degree of plasticity in its diet by feeding on both benthic and pelagic prey (Coria et al. 2000; Clausen and Putz 2002; Lescroël et al. 2004). Feeding typically occurs in in-shore waters, with birds seldom foraging beyond 30 km from the colony during the breeding period (Trivelpiece et al. 1986; Wilson et al. 1998; Miller et al. 2009). Furthermore, during the chick-rearing period gentoo penguins typically forage during the day with trips rarely exceeding 24 h (Croxall et al. 1988; Williams and Rothery 1990; Masello et al. 2010). This behaviour makes gentoo penguins a well-suited model species for the use of animal-borne camera loggers as foraging occurs during daylight when illumination levels are highest and, despite limitations in terms of battery life, cameras can capture important foraging events because of the relatively short and near shore foraging typical of this species.
Materials and methods
The study was conducted at Cow Bay (51°26′3.5′′S, 57°52′39.2′′W), which lies in the northeast of the Falklands archipelago with approximately 1800 breeding pairs of gentoo penguins (Baylis et al. 2013). Fieldwork took place during the guard period of chick rearing in December 2013. In total, 20 birds were equipped with devices to the midline of their backs, which included a CEFAS G5 TDR (31 × 8 mm, 2.7 g, CEFAS Technology Ltd., Lowestoft, UK), CatTraQ GPS logger (44 × 27 × 13 mm, 22 g, Catnip Technologies) and Replay XD 1080 HD video camera estimated to record for 120 min at 30 frames per second (with custom case: 110 × 35 mm, 148 g, Stable Imaging Solutions, USA), cumulatively weighing 172.7 g accounting for 2.7 % mass of the instrumented bird. The camera was secured in a position, which allowed for just the top of the head to be filmed. The TDR was secured to the top of the GPS and placed directly behind the camera.
During the breeding period, gentoo penguins at Cow Bay depart on foraging trips early in the morning (approximately 05h00–07h00). As adults headed toward the sea, they were captured with a net attached to a 2-m pole (Masello et al. 2010). Bill length and depth were recorded with Vernier callipers to the nearest 0.1 mm. All units were attached to the birds with waterproof adhesive TESA® tape (Beiersdorf AG, GmbH, Hamburg, Germany). Just prior to securing the camera the device was turned on and a reference time taken from a watch synced with the TDR time. A continual watch was made until 23h00 so as to recapture birds before they entered the colony.
Dive data were analysed using the diveMove package (Luque 2007) in R 3.1.2 (R Core 2015). Specifically, depth data were manually zero offset corrected and a 3-m-depth threshold was chosen to identify dive events.
Animals acquire resources in many ways, and this diversity allows for many types of interactions amongst animals. This first recording of attempted intraspecific kleptoparasitism at sea by a penguin was only possible with the recent advances in camera logger technology. This behaviour does occur in penguins on land; however, it is restricted to the stealing of nest material (Carrascal et al. 1995) rather than food. This is certainly a rare event as no other footage from our study has yielded observations of this nature. Of the six ecological and behavioural conditions determined by Brockman and Barnards (1979) for this event to occur, two factors support the reason for this behaviour. First, the squid is on the large side of gentoo penguin prey items for those reported previously at the Falkland Islands where the most abundant squid consumed, Patagonian squid (Doryteuthis gahi), had a modal mantle length of 100–110 mm (Clausen et al. 2005). This suggests that the squid specimen was an energetically important prey item. Second, this prey specimen was highly visible, being conspicuously carried in the beak (Senzaki et al. 2014). The large prey item will also require a much longer handling time, increasing the host’s possibility of being kleptoparasitised (Steele and Hockey 1995).
Despite the fact that the conditions for kleptoparasitism to occur were favourable, the pirate bird was still unsuccessful. This lack of success may have been due to an inability to obtain the item on the first attempt (Ratcliffe et al. 1997), thus losing the stealth advantage. However, the effect of the act was clearly detrimental to the prey item causing damage to it, a consequence recognised by Krause and Ruxton (2005). This may have facilitated the third bird obtaining part of the prey item as an individual that initiates kleptoparasitism is not always successful, resulting in a follower or bystander gaining (Hatch 1970).
Further observations will be needed to fully quantify the consequence and cause of kleptoparasitism amongst penguins. With the rapid development of new technologies, resulting in more energy-efficient batteries, this will soon be possible. These answers may lead researchers to greater understand the impacts of food availability on certain penguin behaviours such as kleptoparasitism, which is believed to occur more often in times of poor food resources (Lavers and Jones 2007; Ashbrook et al. 2011).
This project was possible through support of Falklands Conservation. Generous funding support came from the Rufford Small Grants Foundation, Falkland Islands Environmental Planning Department and Nelson Mandela Metropolitan University Research Capacity Department. Additional stipends were provided by the National Research Foundation of South Africa. We are grateful to Jan Cheek and wardens of Johnsons Harbour for access to the study colony. We are extremely thankful to the volunteers who assisted with sample collection. Additionally, the guidance from two anonymous reviewers greatly improved the manuscript.
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