A small New Zealand songbird that hides food for later use provides insights into cognitive evolutions
Dr Rachael Shaw from the School of Biological Sciences discusses the unusual food behaviours of the New Zealand robin.
29 October 2019
When we think about animals storing food, the image that usually comes to mind is a squirrel busily hiding nuts for the winter.
We don’t usually think of a small songbird taking down an enormous invertebrate, tearing it into pieces and hiding these titbits in the branches of trees to snack on later in the day. But this is also a form of caching behaviour, where food is handled and stored for later consumption.
For caching animals, the ability to recall where food is hidden is crucial for survival. My research into the spatial memory performance of a caching songbird, the New Zealand robin (Petroica longipes), shows male birds with superior memory abilities also have better breeding success.
By outward appearances, the small, grey toutouwai (Māori name for P. longipes) is not particularly remarkable. But its noteworthy behaviour includes feasting on some of the world’s largest invertebrates. There is only so much of a 30cm earthworm a 30g bird can eat, and rather than waste the leftovers, toutouwai will cache any surplus prey they don’t want to eat immediately.
For selection to act on a trait, there must be individual variation that is passed onto offspring and that influences survival and reproduction. While researchers had looked at how spatial memory influences winter survival in caching mountain chickadees, no one had examined whether memory performance influences reproductive success in any caching species. Our research tackles this issue.
Measuring memory in the wild
We measured the spatial memory performance of 63 wild toutouwai during winter. We gave the birds a circular puzzle that had a mealworm treat hidden inside one of eight compartments. For each bird, we put the puzzle at the same location in their territory several times in a single day, with the food always hidden in the same spot.
Over time, toutouwai learned the location of the hidden treat and began opening fewer compartments to find the mealworm. We then followed these same birds through the next breeding season and looked at whether their spatial memory performance (measured as the number of compartments they had to open to find the mealworm) was linked to their ability to feed chicks, and whether it influenced the survival of their offspring.
Our results suggested that spatial memory performance influences reproductive success in toutouwai. Males with more accurate memory performance successfully raised more offspring per nest and fed larger prey to chicks.
By contrast, we did not find the same patterns for females. This is the first evidence that spatial memory is linked to reproductive fitness in a food caching species.
If there is such a great benefit for males in having an accurate recall of locations, why aren’t all males the best they can possibly be in terms of spatial memory performance? In other words, why didn’t all the male toutouwai we tested ace our memory task?
Intriguingly, our results suggest a role for conflict between the sexes in maintaining variation in cognitive ability. We found no effect of memory performance on female reproductive success, suggesting that the cognitive abilities that influence reproductive behaviour may well differ for females.
Such a difference between the sexes would ultimately constrain the effect of selection on male spatial memory, preventing strong directional selection from giving rise to uniformly exceptional memory in our toutouwai population.
Our work produced some tantalising evidence for both the causes and consequences of variation in cognitive ability, but it also raises several more questions. For example, while we’ve shown that memory performance matters for males, we still need to examine how it influences caching behaviour.
Another mystery that remains is why spatial memory ability may have less of an influence on female toutouwai fitness. One possibility is that longer-term spatial memory for specific locations (rather than the short-term memory we measured) may matter more for female reproduction, because females do all of the nest building and incubation.
So far, we’ve only provided one piece of the puzzle. To get the full picture of how cognition evolves, we have many more avenues left to explore.
Dr Wokje Abrahamse, Senior Lecturer, School of Geography, focuses on understanding people’s motivations to adopt sustainable behaviours.
Victorious Spring 2019
Scientists are more certain than ever that climate change is happening and that people’s actions are contributing to it. Profound lifestyle changes are needed to avoid the impacts of climate change. Enabling people to adopt sustainable behaviours can form an integral part of the solution to the climate change challenge.
Encouraging people to change their behaviour can be notoriously difficult. Even when people have high levels of environmental concern and a strong willingness to do something for the environment, this does not always translate into action. When it comes to making daily choices, environmental concern is often at odds with concerns such as cost, convenience, or social pressure—to name but a few.
My research focuses on understanding people’s motivations to adopt sustainable behaviours and on the effectiveness of initiatives and policies to encourage behaviour change. In other words, I look at what works and what does not work so well, and why this might be the case.
One commonly held assumption seems to be that people are motivated only by money. Obviously, cost and financial considerations are important to people when they make daily choices, but it is by no means the only motivator. In my research, and that of my students, we have found that people with strong environmental values are more likely to do a range of pro-environmental behaviour, such as conserving energy at home and reducing their meat consumption. It is important that behaviour-change campaigns are aligned with people’s motivations.
So, what is the most effective way to change people’s behaviour? I get asked this question a lot. And I usually respond by saying, “It all depends.” When doing research for my recent book Encouraging Pro-environmental Behaviour: What Works, What Doesn’t, and Why, I found that different kinds of sustainable behaviours are associated with different motivators. In the energy domain, an approach that seems to work quite well is the use of social norms. When people are told that their neighbours are conserving energy, they are then more likely to conserve energy also. This is the power of peer pressure. But in the transport domain, people’s travel habits and their environmental concern play an important role.
Habits refer to our daily routines: we do not think about these behaviours too much, we just do them. Interventions to encourage sustainable transport choices are more effective when people have weak car-use habits and when they have high levels of environmental concern. Research in the area of sustainable food consumption is starting to look into ‘nudging’—by making foods with a low environmental impact the default (e.g. by placing them at the check-out counter), people could be ‘nudged’ into making sustainable choices.
We need urgent action to address current environmental problems. Research findings on what motivates people to adopt pro-environmental behaviours could, and should, be used to inform policymaking. Ultimately, policies that are informed by research from the social and behavioural sciences can benefit people and society in a shift towards a more environmentally sustainable future.
Out of our depth
Dr Mike Joy believes the key to improving New Zealand’s waterways and natural environment is the power of the people. “My message at my public talks is, ‘Your rent for living on this planet is activism’. It’s become clear that if government changes anything, it’s when people push for change,” he says.
Victorious Spring 2019
“The science is clear, and my role is about public awareness and getting as much information as I can to the public about what’s going on.”
Mike, a freshwater ecologist based at the University’s Institute for Governance and Policy Studies, says the main issues are the intensification of agriculture and our failures in wastewater management.
A recent study found drinking water supplies in some parts of New Zealand have nitrate levels more than three times higher than a threshold level for colorectal (bowel) cancer risk.
“The nitrate pollution comes from dairy farming mostly,” says Mike. “Nitrate fertiliser is added to pasture and crops to accelerate plant growth. Much of it enters waterways either directly with rain and irrigation or through animal urine.”
Moving away from farming intensity is a single solution to multiple problems, he says.
“Decrease the number of cows and you reduce the loss of nutrients to waterways, you reduce methane, nitrous oxide, and carbon emissions to the atmosphere, you reduce pathogens that get into waterways, you reduce antibiotic and hormone use, meaning less of both in soil and waterways, you reduce the heavy metal contamination of soil, and you reduce the compaction of soils.
“Focusing on adding value and diversity will give us all a much better future.”
Another recent study has shown 74 percent of New Zealand’s native freshwater fish are threatened or at risk. This compares to 22 percent in the early 1990s.
“The legislation intended to protect biodiversity in New Zealand is neglected and largely ineffectual,” says Mike. “Our native fish are not covered by the Wildlife Act. The only species that the Freshwater Fisheries Regulations from 1983 protects is the grayling—and that went extinct 50 years earlier, in the 1930s.
“Others are protected except if you want to use them for human consumption or scientific purposes, which in practice translates to zero protection. Of our threatened native fish, including whitebait, longfin eel, and black flounder, seven of them are commercially harvested and exported.”
Mike says it’s the past 50 years where we’ve accelerated beyond our boundaries. “New Zealand’s clean green image is crucial to tourism and agriculture, and because we’ve gone backwards too fast and we’re so isolated, people haven’t caught up. It’s the value add to everything we export—and if we lose that, we never get it back.
“Our freshwater systems are in awful shape, and getting worse fast. Our grandchildren won’t be swimming in our rivers, and there won’t be native fish in them either, unless we make changes now.”
Protecting our plants
Tongariro National Park is not just centrally located—it's a central part of New Zealand culture.
Victorious Spring 2019
The park is home to Mount Ruapehu, known as Koro (grandfather) to local iwi Ngāti Rangi. His slopes and the surrounding park are home to several biodiversity hotspots supporting many of New Zealand’s unique plant species—sites that, like many other natural landscapes around the world, are under threat from climate change.
Dr Julie Deslippe from the School of Biological Sciences is working with Ngāti Rangi and the Department of Conservation to help determine how climate change will affect the taonga tipu (sacred plants) living in the park and how they can be protected.“If we don’t work to address the impacts of climate change, the landscapes we engage with on a cultural and spiritual level will be gone. Biodiversity underpins everything—the air we breathe, the water we drink, and the climate we live in,” Julie says.
Julie’s project began by gathering knowledge from Ngāti Rangi on what plants in the area are used by the iwi and their cultural significance. These interviews, led by Ngāti Rangi iwi member Deborah Te Riaki, identified 45 of the most culturally significant plants in the park. Julie’s team then collected data on where these plants grew in the park and how abundant they were. The field surveys, led by PhD student Justyna Giejsztowt, also employed two local school students from Ngāti Rangi, providing a unique on-the-job training opportunity in their own rohe.
“Working with Ngāti Rangi on this project was essential,” Julie says. “The exchange of cultural and ecological knowledge among the members of the team provided a much more holistic understanding of the place.”
There are two major threats to the taonga tipu in Tongariro National Park—increasing temperatures, and the invasion of European heather, a problem weed. Julie’s team created digital models of how these risk factors would impact a representative sample of five of the 45 plants identified by Ngāti Rangi.
Julie says, regardless of the degree of warming, all models predict increasing infestation of heather in the park, with negative consequences for the spread of taonga tipu in the park. However, Julie believes New Zealand has the ability to use this knowledge to make real progress in countering climate change.
“Now we have more information, we can make an informed decision on how to counter this threat and figure out which conservation tools could help preserve these landscapes,” Julie says. “We have the political will and expertise, and the bicultural dialogue in New Zealand is world-leading—if we can manage climate change anywhere, it’s here.”
An expert from Ngāti Rangi is using the information gathered as part of this project to create educational resources for children to help educate all New Zealanders about taonga tipu and how we can help preserve them for future generations.
“We want to help preserve mātauranga Māori,” Julie says.
Wet and wild
Fourteen years ago, the Wairio block on the eastern shores of Lake Wairarapa was an area of barren paddocks, boggy pasture, and few obvious prospects for biodiversity.
In 2011, Stephen was given free rein to carry out a large-scale field experiment to try to restore a kahikatea ‘swamp forest’—a forest that is inundated with freshwater, either permanently or seasonally—on the land.
Driven by a desire to test and improve habitat restoration, Stephen and postgraduate students from the University trialled five different techniques for suppressing tall fescue—an invasive grass species that smothers and prevents tree seedlings establishing. They planted a five-hectare block with 2,500 trees of eight species, including kahikatea, tōtara, mānuka, and ti kouka (cabbage tree), among others. “After eight years, many of the trees are well over three metres tall and setting their own seed,” says Stephen.
“Due to increased winter flooding of the area, not all of the original trees survive today. But regular monitoring of growth and survival has enabled us to gain a better understanding of each species’ environmental tolerances—how trees help each other, and which species to plant where in the remainder of Wairio,” he says.
“Now that the planted trees have the upper hand over tall fescue, a process of natural regeneration is starting to take hold. A large number of birds are using Wairio now. We have a variety of native ducks and black swans, and small flocks of royal spoonbill that have not been seen in this area for many years.”
The secretive and critically endangered Australasian bittern, or matuku, now call Wairio home too, and the hope is that their numbers will climb as the cover of reed bed—the matuku’s preferred breeding habitat—increases.
But the benefits of the restoration and the University’s involvement don’t end there. The rejuvenated wetland will play a key role in cleansing nutrient-rich water, which flows off surrounding farmland, before it enters Lake Wairarapa. Stephen also estimates that the restoration plantings have absorbed four to five tonnes of carbon so far—a figure that will increase exponentially over the coming years as growth of the larger trees accelerates.
The project, which was carried out in partnership with conservation group Ducks Unlimited New Zealand, the Department of Conservation, and the Greater Wellington Regional Council, has become a focal point for practical research and community collaboration, with other academics from the University’s Landscape Architecture, Science and Society, Geography, and Biological Sciences programmes developing transdisciplinary research and teaching links with the Wairio Wetland Restoration Trust and local Ngāti Kahungunu iwi.
Stephen says the project could also help to set the direction for future conversations about biodiversity in New Zealand.
“My hope is that our work here will inform future restoration activities, highlighting the important functions of wetlands and demonstrating the numerous gains that are possible when communities and researchers work together for sustainable and equitable futures.”
Honey bee-harming Varroa mites also a threat to other insects
New research has shown that the Varroa mite, which is a major causes of honey bee mortality, could also pose an indirect threat to many other insect species.
The study was carried out by researchers at Victoria University of Wellington, the Malaghan Institute of Medical Research and the University of California Riverside.
“The Varroa mite has spread throughout most of the world and is one of the biggest threats to honey bees,” says Professor Phil Lester from Victoria University of Wellington’s School of Biological Sciences. “Our research shows that the introduction of this mite could also have serious consequences for spiders, as well as butterflies, beetles, ants, and many other insects.”
The reddish-brown Varroa mite is a specialist parasite of honey bees and is about the size of a pinhead. It was found in New Zealand in 2000 and accidentally introduced into Hawaii in 2007-08.
The Varroa mite carries a range of other viruses and pathogens with it as it moves into new ecosystems, Professor Lester says.
The research completed by Professor Lester and his colleagues, and published today in Proceedings of the Royal Society B, shows that these viruses and pathogens affect a wide range of hosts.
“In particular, our study showed that the yellowjacket wasp, a honey bee predator, had been infected by strains of viruses carried by the Varroa mite, likely as a result of attacking and eating infected honey bees,” says Professor Lester. “It is likely these strains have spread to many other species’ too.”
The introduction of the Varroa mite in Hawaii has also led to the emergence of new, virulent strains of the Deformed Wing Virus (DWV). Current strains of this virus are responsible for the death of many honey bee populations worldwide.
“The arrival of the Varroa mite in honey bee populations in Hawaii has favoured a few virulent strains of DWV,” says Erin Wilson Rankin, an assistant professor of entomology at the University of California Riverside and lead investigator of the study. “The effects of the Varroa mite have cascaded through entire communities in Hawaii and probably around the world.”
The study focused on populations of honey bees and yellowjacket wasps, a common predator of honey bees, that live in Hawaii. The research analysed these insects before and after the introduction of the Varroa mite to Hawaii in 2007.
“Varroa is a serious issue for honey bees that needs to be managed,” says Professor Lester. “Our research shows that managing the Varroa mite will help many other insects as well.”
This research was supported by a Royal Society Te Apārangi Marsden grant, the United States National Science Foundation, the Hellman Fellows Fund, and the National Institute of Food and Agriculture of the United States Department of Agriculture.