Urban ecology of an endemic pigeon, the kererū

Abstract

Urban areas are continuing to grow and intensify to accommodate an increasing urban human population. While urban areas can be challenging places for wildlife, some species have adapted to these novel environments. However, as urban areas continue to develop, there is a danger that without careful planning, those characteristics of urban areas that support urban wildlife could disappear. The presence of urban wildlife in cities can benefit urban residents through the provision of ecosystem services and can help residents form connections with nature, and, in the case of indigenous species, can help to create a unique sense of place. Kererū (New Zealand pigeon; Hemiphaga novaeseelandiae), a large frugivorous pigeon, are one of the few endemic bird species to regularly occur in urban areas in New Zealand, although at relatively low densities. Kererū are important seed dispersers for many plant taxa, and as an easily identifiable and charismatic species, they are an ideal species to promote urban conservation. This thesis investigates the urban ecology of kererū in Auckland, New Zealand’s largest city, by investigating kererū distribution across the city, urban kererū diet and the space‐use and movement of kererū in urban and peri‐urban areas. Human modification of the landscape can lead to changes in a species space‐use and movement behaviours. ARGOS satellite telemetry was used to track the annual space‐use and movements of 13 kererū in urban and peri‐urban areas of the Auckland region. The majority of the tracked individuals remained localised throughout the year in a single home‐range area (mean ± one standard error = 326 ± 45 ha), suggesting that sufficient resources are available throughout the year. However, one individual was more transient and was recorded in three discrete areas separated by 35 km and 45 km. This individual is estimated to have travelled at least 270 km during a 40 day period. Much of the previous work on kererū space‐use and movement has used radio‐telemetry, which can miss longdistance movements if the individual flies out of range. The use of satellite telemetry, as in this study, increases the likelihood of detecting the infrequent long‐distance movements as observed for this one transient individual. Monitoring urban wildlife can help inform conservation and urban planning decisions but it can be logistically difficult due to the large amount of privately owned land. Involving members of the public through citizen science projects is one solution, although there are many potential sources of error and bias that must be addressed. The ‘Auckland Kererū Project’ was a local web‐based project created to collect data on kererū occurrence in the city and on the resources available to kererū in residential gardens. A total of 311 people participated in the project during the two years (April 2014‐2016) that it was running, with most people only contributing to the project once. Large increases in participation occurred immediately following high profile media releases, but did not continue. Participation was also spatially uneven and associated with socio‐economic status; most participants resided in more affluent suburbs. Despite the potential biases, citizen science remains a useful tool particularly for collecting data on low‐density species in urban areas as there are high numbers of potential observers. Understanding a species current distribution in urban areas and the environmental variables that are most important in predicting it, can help inform conservation policies and identify areas of importance to ensure a species continued persistence in urban areas. In this study, a maximum entropy species distribution modelling approach was used to characterise kererū distribution across urban Auckland, using kererū occurrence data collected by members of the public. The estimated relative probability of kererū occurrence was unevenly distributed across the city, with areas of higher probability occurring in the north and central city. The two main predictors of kererū distribution were distance to indigenous forest and amount of vegetation cover (5 ‐15 m in height) per hectare. South Auckland had, on average, less vegetation cover and fewer patches of indigenous forest and as such had lower estimated relative probability of kererū occurrence. These variables may be correlated with socio‐economic deprivation in some parts of the city. One impact of urbanisation is that it can alter the availability of resources for urban wildlife, through the reduction and fragmentation of indigenous vegetation, combined with the addition of many exotic plant taxa and other novel anthropogenic resources. A flexible diet is a useful strategy for species adapting to urban environments. I used feeding observations collected through the ‘Auckland Kererū Project’ as well as my own observations, combined with analysis of stomach contents to assess kererū diet. In addition, a garden plant survey and a focal plant phenology study were used to investigate resource availability. Kererū were recorded consuming 28 indigenous plant taxa and 23 exotic plant taxa, but 69% of feeding observations were on just six taxa; pūriri (Vitex lucens) 24%; kōwhai (Sophora spp.) 14%, plum (Prunus spp.) 8%, nīkau (Rhopalostylis sapida) 7%, loquat (Eriobotrya japonica) 7%, and guava (Psidium spp.) 6%. Pūriri was also the most common plant taxa recorded in residential gardens and as it produces fruit throughout the year, it is an important component of urban kererū diets in Auckland. Loquat and guava, two introduced, potentially invasive taxa, appeared to be highly attractive to kererū, which may be of concern due to the seed dispersal capabilities of kererū. Despite the year round availability of fruit, vegetation was also consumed throughout the year, but the proportion of vegetation in the diet was highest in winter and spring. There were very few observations of kererū consuming tawa (Beilschmiedia tawa), taraire (B. tarairi) or miro (Prumnopitys ferruginea), all of which are plant taxa with highly nutritious fruits that are important components of kererū diets elsewhere. Currently, urban areas appear to be satisfactory substitute habitat for kererū in Auckland, but more could be done to ensure the availability of food resources throughout the year. Additionally, it would be constructive to address the socially unequitable distribution of trees in Auckland as this would increase habitat for kererū (and other species) across the city as well as ensuring residents across the city gain the benefits of urban wildlife and trees. Kererū are a well‐liked part of the urban biota and an ideal species to promote urban conservation.