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Animal Behaviour 77 (2009) 273–274

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Animal Behaviour

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In Focus

Featured Articles in This Month’s Animal Behaviour

Figure 1. Yellow-eyed penguins are major tourist attractions, but they are sensitive tohuman disturbance, especially those with particular personality traits. Photo: UrsulaEllenberg.

Penguin Preservation

Yellow-eyed penguins are rare, endemic and endangered. Theyare also highly engaging, charismatic creatures (Fig. 1). Unsurpris-ingly, they are a key attraction for ecotourism operations, whichhas led to concerns that tourist-related pressures could have adetrimental effect on population numbers. As Ursula Ellenberg,Thomas Mattern and Philip Seddon note in this month’s issue(pp. 289–296), understanding how well penguins cope withhuman-related disturbance is key to ensuring that the needs ofthese animals are not compromised by their popularity with thepublic. Specifically, identifying individual differences in stressresponses, based on the birds’ temperament, makes it possible toassess whether animals really do get used to the presence ofhumans and learn to ignore them (they ‘habituate’) or whetherthe decline in response to humans could be caused by a shift inpopulation composition: shy animals, for example, may leave anarea in which human disturbance occurs, or fail to reproduce. Asyellow-eyed penguins are known to be sensitive to human distur-bance, and show reduced breeding success in areas with unregulatedvisitor access, a systematic investigation of individual differences inresponse is crucial to the management of such an endangered species.The needs of the most vulnerable members of the population canoftenmake all the difference to conservation efforts.

To investigate the penguins’ stress responses, Ellenberg andher colleagues measured the animals’ heart rate using an inge-nious device: an egg-shaped microrecorder that was added tothe other eggs in the penguins’ nest. As the penguin settles onthe eggs to incubate them, the microrecorder picks up their heart-beat and transmits it to the researchers’ hide. Based on thepenguins’ response when the fake egg was placed in their nest,Ellenberg and her colleagues classified them into three groups:timid, calm and aggressive. The researchers then conducteda series of disturbance experiments, in which a person walkedslowly and steadily up to a nest, stopped a short distance away,waited for a minute and then walked away. They also looked atthe responses of penguins before and after an habituation period,during which penguins were regularly visited by the same personat midday for 5 consecutive days.

Ellenberg and her colleagues found that female penguins tooklonger to recover from the stress of a visit by a human (i.e. it tooklonger for their heart rate to return to normal) than males, andthat this response was also dependent on their temperament:calm and timid females needed much longer to recover thanaggressive ones. Following the 5-day visiting period, most penguinsshowed shorter recovery times than they had prior to the visits, but

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again sex and temperament had an influence: females showeda much greater drop in their recovery times than males, whilecalm birds, although responding strongly to humans in the distur-bance experiments, showed much shorter recovery times followingthis more lengthy exposure to humans. Aggressive individuals, in

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Figure 2. Formica integroides workers attacking a glass bead coated with cuticularsecretions from Formica xerophila workers. Photo: Colby Tanner.

In Focus / Animal Behaviour 77 (2009) 273–274274

contrast, did not display this flexibility and did not habituate: theyshowed a similar response before and after the 5-day period.

These findings have implications for both evolutionaryprocesses and management policies. Evolutionarily, a lack of habit-uation by aggressive individuals makes them more vulnerable tobreeding failure and, in the long term, could mean the loss ofaggressive individuals from the population. This could have majorconservation implications if aggressive individuals are better ableto survive other kinds of environmental challenges, such as changesin predator density. And, of course, the preservation of geneticdiversity is crucial to the long-term viability of wild populations,so any factors that reduce diversity need to be controlled.

Ellenberg and her colleagues also emphasize that we, as tourists,can make a difference by ensuring that we only book tours atappropriately managed sites, where nest disturbance is minimized.They also strongly argue that human disturbance at the majority ofyellow-eyed penguin breeding sites should be limited to research-based activities, given that some individuals fail to habituate toeven the presence of one silent, steady individual, let alone a bunchof chattering tourists. Let’s hope that Ellenberg and her colleagues’paper will serve as a wake-up call for preserving this charismaticspecies, and not as the penguins’ epitaph.

Louise BarrettExecutive Editor

Dominant Ants

How do animals adjust their behavioural responses so theiractions are appropriate to the situation? If a species is inclined tobe aggressive, can individuals modulate their behaviour if aggres-sion is either pointless or risky? Can a member of a more submis-sive species summon aggression in critical situations? In thisissue Tanner and Adler (pp. 297–305) address these critical ques-tions in a study on ants.

Ants in the genus Formica are abundant in northern temperateecosystems. Typically, several species in this genus co-occur withina temperate community and, because they have similar feedingniches, Formica species compete for food and space. While allmembers of this genus lack the ability to sting, some Formicaspecies are pugnacious in their encounters with other ground-dwelling invertebrates and have the ability to dominate territorialinteractions or contests for food. Other Formica are more submis-sive; studies of food webs in temperate ground-dwelling inverte-brates often propose dominance hierarchies among species in thisgenus. These hierarchies correlate with access to food and nestingsites.

Tanner and Adler address how context can affect dominance andaggression in a pair of Formica species that co-occur in communi-ties in the western United States. Formica integroides (Fig. 2) islarger and more aggressive than Formica xerophila, which is usuallyregarded as a submissive species. Formica workers can typicallydiscriminate between nestmates and non-nestmates by perceivingthe mix of surface chemicals, or cuticular hydrocarbons, on the antsthey encounter. Nestmates carry similar hydrocarbon mixtures,while non-nestmates differ in the relative concentration ofcompounds within the mixture. These differences are usuallyadequate to make discriminations between colonies within

a Formica species, and are even more pronounced between species.Cuticular hydrocarbon differences provide an immediate mecha-nism for a foraging ant to make ‘friend versus foe’ determinationsand to react appropriately.

Tanner and Adler staged encounters between ants of these twospecies and observed aggressive outcomes. In addition, usinga clever technique of coating glass beads with cuticular hydrocar-bons extracted from ants, Tanner and Adler were able to assesshow context affects aggressive or defensive reactions in these twospecies, and to compare how a ‘dominant’ and a ‘submissive’species react in a given situation. Because the glass beads do notreact to an attack, Tanner and Adler were able to partition thebehaviour of the ant initiating a contest from the effects ofa responding ant.

Their key finding is that expression of aggression is contextdependent in these Formica ants. This is consistent with findingsof other investigators whose study organisms were birds ormammals, and this result suggests that context dependence isimportant even in animals that often receive little credit for cogni-tive abilities.

Two factors stand out in the modulation of aggressiveresponses by F. xerophila. First, xerophila workers respond morestrongly to strangers, ants from previously unencountered colo-nies, than to neighbours. Territorial boundaries and resourceaccess are probably already resolved with neighbours. Lowerintensity encounters with them probably reduce costs by elimi-nating unnecessary fights. Strangers are a more serious threatand are dealt with accordingly. Second, the strongest responsesare observed in ants defending aphid-bearing trees, a rich foodresource for these ants; response is associated with the value ofthe resource being defended.

Tanner and Adler conclude that a simple dominance hierarchybetween the species does not capture the complexity of thissystem; by responding in a context-dependent way, the seeminglysubmissive F. xerophila workers are able to protect the resourcesthat matter the most.

Michael BreedExecutive Editor