Page 6 - Ratel 2023 Summer

Ratel volume 50, issue number 2

Current Zoo Science for Zoo Keepers

From the BIAZA Research Committee

Welcome to the next instalment from the BIAZA Research Committee, subjects’ tanks using adhesive Velcro strips on all four corners of the
bringing science directly to zoo keepers. Once again, we will be applying acrylic sheet, and each of the backgrounds remained in place for seven
recent scientific papers to zoo animal husbandry by picking out the key days at a time.
points from longer research articles and condensing them down into a
more manageable format. We hope you can see the relevance of such Stress-linked behaviours in this species were identified as swimming and
research to your own work caring for the myriad of wild animals in British resting (Dias et al., 2022). Swimming was stated as the behaviour which is
zoos In this article, we will review a study investigating the effects of most positively associated with stressors in this species, whilst resting is
background colour on stress-linked behaviour in Lake Oku clawed frogs, simply the behaviour most traded off against an increase in swimming
and another detailing why active use of resources or enrichment by animals behaviour. All background colours elicited, to varying degrees, an increase
may not be required for the stimuli to have welfare value. in swimming and a decrease in resting behaviour immediately after
installation. These results indicate a stress response to the change in
Optimising welfare in zoo-housed species is critical in maintaining good background colour and likely the associated vibrations caused when
health and maximising conservation breeding success. Zoo animals are making the change. Of the four treatments, the green and grey
exposed to a multitude of stressors which may include social groupings, backgrounds resulted in the smallest initial increase in swimming and
visitor presence and enclosure design. Whilst acute stress can be beneficial decrease in resting, suggesting that these backgrounds may have mitigated
in certain situations, namely the ‘fight or flight’ response, chronic stress some of the stress response to change. The authors note that green and
can damage health by causing atrophy of healthy tissues which then leads grey background colours may enable camouflage of frogs most effectively
to damage of critical organs and blood vessels. Given that good physical because grey is most similar in colour of the X.longipes, and the green
condition is necessary for the welfare of any animal, impairment of these background imitates the aquatic plant life of Lake Oku. Similar results
functions will result in poor captive welfare and consequently reduced have also been noted in the African clawed frog (Xenopus laevis) which are
reproductive success. known to rely on cryptic camouflage. Increased corticosterone release,
increased stress-associated behaviours and a reduction in body mass has
The welfare of amphibians is an understudied area of research, and been observed in X.laevis when housed with non-ecologically relevant
developing knowledge is vital to enhance amphibian care and ex situ background colours (Holmes et al., 2016).
conservation goals. Graves et al. (2023) investigated the effect of different
background colours on stress-linked behaviour in 24 wild-caught adult This study acts as an initial investigation into the effect of background
Lake Oku clawed frogs (Xenopus longipes), obtained legally and ethically colour on newly developed behavioural indicators of stress in X.longipes.
from the wild in 2008, housed at ZSL, London Zoo. The frogs were Validation of this behavioural measure via corticosterone, as has been
exposed to four different background colours: green, grey, black, and demonstrated in X.laevis, is a key next step in improving the robustness
none, the order of which was randomly allocated. These colours were of stress indicators in X.longipes.
selected based on how they reflect the colours found in the natural habitat
of the X.longipes. Acrylic sheets were attached to the back of the study The second article presents a review regarding the current evaluation of
enclosures and enrichment which typically focus on the animals’ active
interactions with these elements (Decker et al., 2023). The authors state
that whilst this method has ‘undoubtedly improved the welfare of
zoo-housed animals over the last 30 years or more’, experiences and
behaviours that do not rely on active interaction with stimuli or resources
have largely been ignored. Interaction has been embedded into enrichment
assessment protocols because it is easy to access and helps to make more
compelling exhibits. However, items which elicit little, or no interactions
can still reduce stress and improve well-being. One concern with a bias
towards valuing active interaction is that the welfare of animals whose
engagement with the environment is more subtle, like reptiles, amphibians,
and fish, is inherently less studied.

The evidence that Decker et al. (2023) present largely comes from research
on humans, lab animals and farm animals, but also applied across a handful
of zoo studies. Studies in American mink (Neovison vison) were the first to
show that time spent in active use did not reflect resource value; when
mink were given free access to compartments containing different
resources, the results showed that they spent four times longer using a
nest box of hay, than swimming in a bath (Cooper and Mason, 2000).
However, if access was weighted, mink worked harder to gain access to
the water bath rather than the hay and stress cortisol levels increased if
denied access to the bath (Mason et al.,2001). Laboratory zebrafish (Danio
rerio) provided with artificial plants show increased female fecundity (Wafer
et al., 2016), and when housed with plants and gravel have been shown to
elicit greater resilience to acute stressors like being chased by a net or
exposure to novelty (DePasquale et al., 2019; Giacomini et al., 2016; Manuel
et al., 2015; Marcon et al., 2018), despite never having experienced
predation or being in a wild habitat (Schroeder et al., 2014). Finally, a pair
of polar bears (Ursus maritimus) were given access to a small indoor den in
addition to their outdoor enclosure during the day and whilst they used
this den for just 2% of the total observation time, having this option
reduced their stereotypic behaviour by about 20% (Ross, 2006).
Lake Oku clawed frog ( ) at ZSL London Zoo (photos
by Sam Whitbread and Naomi Frost).
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