Animal & Population Management

Scientific Papers


A comparative study of nightly allonursing behaviour in four zoo-housed groups of giraffes Giraffa camelopardalis (Zoelzer et al., 2020)

August 03, 2020

Abstract: In the wild, giraffes Giraffa camelopardis have a pronounced and complex social structure, which is characterised, for instance, by the joint rearing of calves. Allomaternal behaviour results in the formation of nursery groups and the suckling of non-filial calves. Despite externally determined group size and composition, this behaviour has also been observed in zoological institutions. It is believed that this study is the first to focus on the nocturnal allomaternal behaviour of four giraffe herds in three German and one Dutch zoos. Using video recordings of 30 individuals over 12 nights, all allonursing events were analysed using the continuous behaviour sampling method. Substantial differences were observed among the four zoos in the frequency and nightly course of allonursing behaviour. In all zoos, allonursing occurred in roughly two periods during the night, which were highly variable in length according to the zoo. A combination of the nocturnal activity, group persistency and group size seems to drive allonursing behaviour in the analysed giraffe groups. Additionally, the composition of allosuckling calves is zoo-specific and includes two to three animals. The results show that allomaternal behaviour in the observed zoos can rather be explained with the milk-theft-hypothesis than with the theories of misdirected-care or reciprocity. Overall, the study showed that nocturnal group-housing of giraffes of various ages enables allonursing and therefore complements natural behaviour by the formation of nursery groups.

Photo credit: Zoo Osnabrück

Animals are designed for breeding: captive population management needs a new perspective (Kaumanns et al., 2020).

May 14, 2020

Abstract: The article deals with the sustainability and breeding problems as reported from many captive populations of birds and mammals. The problems are considered under the perspective of basic management paradigms: the “small population” and the “declining population paradigm”. It is elaborated that under the latter, better options to support the long-term survival of populations can be developed by analysing the reasons for the decline and by emphasising the role of the individuals and their breeding performance. The development of a population and the breeding performance are strongly interrelated. It is therefore proposed to manage a population predominantly as a “breeding device” and the individuals as its constituents that are “designed for breeding”. Following life history theory, individuals have to be regarded as phenotypes. Regarding them as the units of management with all their fitness related properties allows the establishment of an integrated management approach that covers their various levels (genotype, ethotype (physiology, behaviour) etc.) on the same level of importance. The organisation of management is proposed to be oriented on the species’ key traits – primary determinants of fitness in a given condition and the species’ typical design for breeding. With reference to the altered conditions of captivity, the preservation of the breeding potential in a population is emphasised. It would require coming close to patterns of reproduction and corresponding life history patterns in natural populations. Larger population sizes would be necessary, thus also producing surplus problems that need to be dealt with. Genetic management should be part of the integrated management approach, follow natural population dynamics and concentrate on the breeding units.

Photo credit: Berlin Zoo

Reduction of Aggression in a Captive Prairie Dog Colony Through Observation and Underground Burrow Mapping (Byun et al., 2019)

August 11, 2019

Abstract: In 2015, staff at the Connecticut’s Beardsley Zoo reported seeing high levels of aggression within their exhibit prairie dog colony. Through RIZE (Research, Internships and Zoo Education), a service learning partnership between Fairfield University and The Connecticut’s Beardsley Zoo, we set out to better understand the potential sources of aggression by documenting the colony’s behavior and developing underground burrow maps, in order to minimize hostility and reduce instances of individual injury. Our observations and burrow maps suggest that this colony consists of two distinct coteries and that territorial food aggression between individuals of these different coteries was the principal cause of hostility. To test this hypothesis, we requested that zoo staff distribute the food within the enclosure so each of the two coteries had equal access to food.  The redistribution of food according to coterie boundaries resulted in a sudden and dramatic decrease in aggression and fighting within the captive prairie dog colony. This study underscores the importance of regular observational work in understanding the dynamics of multiple individual exhibits and highlights the positive and practical impact that programs like RIZE can have for institutions like zoos and aquariums.

Photo credit: Connecticut's Beardsley Zoo

Sexually Dimorphic Growth in the Western Swamp Tortoise, Pseudemydura umbrina (Testudines: Chelidae) (Durell & Keeley, 2019)

August 01, 2019

Abstract: Captive breeding of the critically endangered Western Swamp Tortoise (WST: Pseudemydura umbrina) has occurred at Perth Zoo as part of the species’ recovery plan since 1988. The first release of captive bred individuals took place in 1994.  Individuals are primarily released into protected wild reserves at approximately three years of age, when they typically reach the mandatory minimum body mass of 100g. They are sexually immature at this age, and gender determination is not possible by external physical examination. For sustainable reintroduction programs, it is desirable to know the sex ratio of individuals prior to release, and the sex of individuals being retained for future captive breeding purposes. Utilising body mass and size morphometrics from zoo bred individuals retained until sexual maturity, we evaluated sex related changes in growth rates and body size over time. Sexual dimorphism in favour of males was first detected at four years of age, with significant differences (P < 0.05) observed in both the body mass (121.9±6.8 g vs 105.0±4.4 g) and carapace length (89.5±2.0 mm vs 83.2±1.4 mm).  Age at which sexual maturity was attained varied between 5 to 13 years, but on average occurred earlier in males (8.0±0.5 yr) than females (8.7±0.4 yr). Data confirm a faster growth rate and earlier age of sexual maturity in males than females, as well as a smaller size (carapace length) at sexual maturity (~110 mm for males and ~100 mm for females) than previously reported for wild WST (110 – 131 mm).  We suggest that using growth rate data, body size (mass and length) and plastron shape may be useful to determine sex at 4-5 years of age, and prior to release to the wild, to better monitor sex ratios at release and during future in situ monitoring.

Photo credit: Perth Zoo

Comparative Personality Traits Assessment of Three Species of Communally Housed Captive Penguins (Pastorino et al., 2019)

June 23, 2019

Abstract: Understanding animal personalities has notable implications in the ecology and evolution of animal behavior, but personality studies can also be useful in optimizing animal management, with the aim of improving health and well-being, and optimizing reproductive success, a fundamental factor in the species threatened with extinction. Modern zoos are increasingly being structured with enclosures that host different species, which permanently share spaces. This condition has undeniable positive aspects, but, in some species, it could determine the appearance of collective or synchronized behaviors. The aim of this study was to verify, in a colony of three species of communally housed penguins (Pygoscelis papua, Aptenodytes patagonicus and Eudyptes moseleyi), through a trait-rating assessment, if interspecific group life impacts on the expression of personality traits, and if it is possible to highlight specie-specific expression of personality traits, despite the influence of forced cohabitation. For many of the personality traits we analyzed, we have observed that it was possible to detect an expression that differed, according to the species. From a practical point of view, these data could ameliorate the management of the animals, allowing to design animal life routines, according to the different behavioral characteristics of the cohabiting species.

Photo credit: Edinburgh Zoo

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