Biodiversity conservation on zoo grounds
While support for in situ conservation is the most important direct conservation measure that zoos can take, zoo grounds can also be home to a surprising number of wild species. Not all of that wildlife is as iconic as the colugos in Singapore, but most zoos are either green patches in a city or built in the forest on the city edge. This means that many zoos have the potential to harbour a good amount of biodiversity. Zoo grounds don’t have much impact on conservation at the national level and never will, but they can be a great place for education. It also makes sense for an organisation concerned about wildlife to be as wildlife friendly as possible. Unfortunately a lack of knowledge among zoo people about native ecology means that that potential is often not realised. Many zoos in recent years try to do something positive, but good intentions do not always lead to good results. The road to hell is paved with good intentions and this is certainly the case for native biodiversity in zoos.
Promoting local biodiversity starts with the plant life and this is often where it already becomes obvious that zoos tend to employ horticulturists instead of biologists when choosing planting. That is not strange, given that zoos are in fact gardens, not wildlife reserves (with exceptions). To promote local biodiversity the start is always to get the right plants. To make a real impact one would have to work with native plants, which are not only native to the country, but also native to the area where the zoo is located. A good example is the hart’s tongue fern (Asplenium scolopendrium), which while native to the Netherlands, only occurs in the chalk-rich south and preferably in forest with rocks. This is however a plant one can easily buy in garden centres and is used in a large number of zoos. But while it is native to the country, it does nothing to promote local biodiversity, as most other species associated with the same habitat just don’t occur there. Even if you have found a plant species that fits the area (and thus also the soil type!), it is also crucial to use local stock. Many plant species have quite a wide distribution, but differ in chemical composition across their range, so if you use the wrong locality, the plant might not be edible for the insects associated with it. These are often two steps too many for most zoos. What you generally see is a standard seed mixture that is colourful and looks good for humans, but is in reality only nice for the most common generalist species. That means that you can attract bees and butterflies with it, but only the common ones and not the ones in need of any extra habitat.
Even the rainforest zoo of Singapore is covered with non-native tree species. (Picture by @marmolady )
Another issue is the use of trees in zoos. In many zoos the majority consists of non-native species that are of little importance to native species. This is even true for Singapore, which is considered a rainforest zoo. While there is some impressive wildlife around, it is mostly the generalist species that only care about structure. In European zoos northern red oak (Quercus rubra), black locust (Robinia pseudoacacia) and sycamores (Platanus spec.) are commonly found, despite being non-native or even invasive. Cavity nesting birds generally don’t care what tree they build their nest in, so one can find middle-spotted woodpeckers and other old forest birds in zoos with exotic trees, as it is all about structure. Invertebrates do however care, and bar a few generalists, such trees are worthless for biodiversity. So also here it would make sense to focus on native trees (also native to the specific area, not just the country) whenever possible.
Of course zoos also use trees and other plants to theme areas to look like Africa or some other exotic location, I am not arguing that that shouldn’t be done, as local biodiversity conservation shouldn’t be the main focus of a zoo. But care should be taken that you don’t plant invasive species. A good example here is pampas grass (Cortaderia selloana), which is a common garden plant and often used in S-American exhibits. Planting it is fine in NW-Europe, but in Southern Europe, as well as in part of the United States this is an invasive species. Zoos should be conscious about what they are planting, not only about what is now invasive, but also about what is likely to become invasive with climate change. Black locust (R. pseudoacacia) is a good example of that, it isn’t invasive yet in the Netherlands, but already so in Eastern Germany. There is a good chance that with warmer weather it will become invasive in the Netherlands too. Having invasive species spreading from a zoo ground would not look good and be bad for native biodiversity. Zoos already don’t have the best name as a source of potential invasive animals, like sacred ibis, but the potential negative impact of invasive plants can be huge too and be even more consequential than animal invasions.
While pampas grass can be great in a S-American exhibit, it is best not done in some parts of the world. (Picture by @Zooplantman ).
When moving from plants to animals, an important group for biodiversity conservation on zoo grounds are insects. Of all insects the pollinators: bees, butterflies and hoverflies are some of the most well-known and well-liked insects and a group that many zoos try to make an effort to have on their zoo grounds. Unfortunately most zoos fail to cater to more than a few common generalist species. The most important problem that most butterflies have very specific host plants for their caterpillars and are not very mobile. Many bees have very specific feeding requirements too, often feeding on only one species or genus of flowers. When as most zoos you don’t take that into account, you are left with a few mobile generalist species not in need of any help. Many zoos now have so-called insect hotels, that if constructed correctly (also a common mistake) can provide nesting opportunities for a number of native bees and other insects. But this omits all ground nesting bees, which are more common and more importantly if you don’t provide the right food source, insect hotels are useless except to generalists. So as long as zoos use the wrong flower mixes and fail to create suitable habitats for all but the most common pollinators, their impact will remain smaller than possible.
Even if for pollinators you provide the right conditions for breeding and feeding, there is another problem: the honey bee. The honey bee is one of the most abundant insects worldwide and although it has an image as a wild species, in many world regions it is a domesticated one and an abundant one at that. Honeybees have a competitive advantage over native species as honeybees can communicate good resources to each other and as such they can take over most of the available flowers, especially given they often occur in unnaturally high densities. There is now abundant evidence worldwide that honeybees do in many cases outcompete native species and are a major reason for decline of wild bee species and other pollinators. Wild bees are however a tremendous biodiverse group, the USA has over 4.000 species and Germany has roughly 600. Even the tiny Netherlands has close to 400 wild bee species, of which over 100 can co-exist in the same area. Zoos do however still mostly focus on honeybees and a very select group of generalists and many zoos even have a hive on their grounds. A single hive can easily have 50.000 individual bees, which are a force to be reckoned with, as many wild bee species occur in relatively low densities and are generally much smaller. Bee hives can be a great tool for education, but are misleading as a tool to save the pollinator. The general public sees the honeybee as the one and only bee and pollinator and this is clearly not the case. So zoos should think again about whether the educational worth of honeybees is worth the potential ecological damage. There are still zoos that promote honey bee keeping as conservation while it is anything but…
Maybe nice for education, not so nice for conservation. (Picture by @vogelcommando ).
While there is clearly potential for some biodiversity conservation on zoo grounds and there are enough steps that zoos could take. It is not the only consideration that goes into landscape design. The main goal of planting in zoos is to enhance the visitor experience, by e.g. providing a nice park landscape or by trying to replicate certain ecosystems. If zoos can achieve that while still providing habitats for native wildlife by using the correct native species when possible and avoid (potentially) invasive species altogether, that would be a nice synergy. The good news is that with some expert advice this shouldn’t be too hard to achieve.
That means we are almost at the end, in the final post I will share some of my thoughts on how future steps in terms of in situ conservation could look like.