The cheeky little kiwi is a New Zealand icon.
Whether you see a kiwi on a $1 coin or branded upon countless gift shop knickknacks, we can agree that it is probably our most iconic species of bird. I mean, an entire country full of people call themselves Kiwi (myself included). However, there is a silent killer lurking. The kiwi housing crisis.
I know what you’re thinking, another story about Auckland’s sky-high house prices, but no. This is not the housing crisis that Mike McRoberts is always talking about on the news. It is a potential killer that relatively little is known about. But before we get to that, some background.
The population of kiwi in New Zealand has been declining for many years. This is almost entirely due to two factors, fragmentation/destruction of their natural habitat, and the introduction of pest species, such as possums, stoats, ferrets, cats, dogs and pigs. As a result of this decline, vast efforts have been put into their conservation.
Captive breeding programmes and relocations to pest-free offshore islands have made great contributions to kiwi survival. Throughout New Zealand you may also stumble upon nocturnal kiwi houses, most likely at your local zoo. There is probably one near you!
These kiwi houses are enclosed spaces that simulate darkness during daylight hours so that you can observe kiwi behaviour up close and personal. Kiwi houses often have soil floors, with native plants. Leaf litter is also brought into the kiwi houses to provide ground cover and to allow the kiwi to continue their natural foraging behaviour. Kiwi houses are rarely used for breeding programmes, as their most important function is to raise awareness and educate the public for the sake of kiwi conservation. However, within these kiwi houses lurks a killer.
Aspergillus is a fungus that is naturally present in leaf litter and other rotting plant material. There are many different species of Aspergillus that are often found in the rotting material on New Zealand’s forest floors. Some of these species cause diseases that affect mammals and birds, including kiwi. Aspergillus affects the respiratory system when inhaled and can cause diseases like pneumonia and aspergillosis in kiwi.
Generally, the amount of Aspergillus found in leaf litter is not high enough to affect kiwi. However, if the conditions are right, and there is a high concentration of Aspergillus, or if the kiwi has a compromised immune system, Aspergillus can be a killer.
Aspergillus is often found in low concentrations in the leaf litter that is brought into nocturnal kiwi houses. However, post-mortem examination revealed that there were 17 captive kiwi deaths caused by Aspergillus between 1997 and 2011 and more deaths have occurred since. There are currently no guidelines for safe levels of Aspergillus present in leaf litter used in kiwi houses.
After identifying this complete lack of knowledge in this area and the potential for harm to kiwi, scientists Travis Glare, Brett Gartrell, Jenny Brookes and John Perrot set out to investigate. They reported their findings in a scientific paper titled “Isolation and Identification of Aspergillus spp. from Brown Kiwi (Apteryx mantelli), Nocturnal Houses in New Zealand”. They surveyed samples of leaf litter from eleven kiwi houses throughout New Zealand and analysed them for Aspergillus spores.
The team found that, for the most part, levels of Aspergillus measured in the leaf litter contained less than 1000 living Aspergillus spores per gram of sampled leaf litter. This may seem like a lot, but remember these spores range from 2.0 – 3.0 micrometres (one millionth of a metre) in size, which is absolutely tiny! Four of the sites showed higher readings of Aspergillus, between 1100 and 8000 spores per gram of material.
One site repeatedly had very high readings of Aspergillus, with some readings showing well over 100,000 spores per gram of material. Woah! This site also had two recent cases where their kiwi had developed aspergillosis because of the high levels of Aspergillus resulting from poorly handled leaf litter. This kiwi house then went through a rigorous management process, lowering the amount of Aspergillus, although it was unable to be eliminated. It seems we have found the culprit responsible for our kiwi housing crisis, but what can be done?
Kiwi are ground foraging birds that require sufficient leaf litter to carry out their natural behaviours. Because of this, simply excluding leaf litter from nocturnal kiwi houses to eradicate Aspergillus is not an option. To me, it is obvious that although an overall captive kiwi management plan exists, guidelines need to be set on the handling and management of leaf litter that is to be placed in nocturnal kiwi houses as well as the overall management of the nocturnal kiwi houses.
Management might include increasing ventilation, lowering humidity and ensuring good sanitation. However, it is hard to create any meaningful guidelines when there is so little known about acceptable levels of Aspergillus in leaf litter. There is still some work to do to find a solution to our kiwi housing crisis, much like the actual housing crisis!
Luke Richards is a postgraduate student who wrote this article as part of ECOL608.