Daria A. Erastova

Sugar-water bird feeding in residential backyards is increasingly popular, but its effects on wildlife are poorly understood. One concern is whether it results in maladaptive behaviour, such as reliance on artificial food or increased aggression due to increased density of visiting individuals. We studied sugar-water feeder-associated bird behaviour in two cities with different climates. We investigate whether season, city, or sugar concentration influenced bird foraging activity and aggressiveness. We then test whether feeder presence affected backyard bird composition. Birds were most aggressive and used sugar-water feeders most actively in winter, especially the omnivorous native tauhou (Zosterops lateralis). We also found city and seasonal differences in sugar-water feeder usage and aggression. Further, in Auckland, the city with the warmer climate, New Zealand’s largest nectarivorous species, tūī (Prosthemadera novaeseelandiae), was more likely to be aggressive at feeders with higher sugar concentrations but foraged longer at feeders with lower sugar concentrations. Neither feeder presence nor sugar concentration influenced garden bird species richness or abundance. We discuss the effects of sugar-water feeding on bird behaviour at the global and local scale and suggest future study directions.

As cities expand, understanding how urbanization affects biodiversity is a key ecological goal. Yet, little is known about how host‐associated microbial diversity responds to urbanization. We asked whether communities of microbial (bacterial and fungal) in floral nectar and sugar‐water feeders and vectored by nectar‐feeding birds—thus forming a metacommunity—differed in composition and diversity between suburban and rural gardens. Compared to rural birds, we found that suburban birds vectored different and more diverse bacterial communities. These differences were not detected in the nectar of common plant species, suggesting that nectar filters microbial taxa and results in metacommunity convergence. However, when considering all the nectar sources present, suburban beta diversity was elevated compared to rural beta diversity due to turnover of bacterial taxa across a plant species and sugar‐water feeders. While fungal metacommunity composition and beta diversity in nectar were similar between suburban and rural sites, alpha diversity was elevated in suburban sites, which mirrored the trend of increased fungal alpha diversity on birds. These results emphasize the interdependence of host, vector, and microbial diversity and demonstrate that human decisions can shape nectar microbial diversity in contrasting ways for bacteria and fungi.

Garden bird sugar water feeding is increasingly popular worldwide, but little is known about its effects on bird health and associated diseases. There is a concern that feeding stations can accumulate pathogens and facilitate pathogen transmission between individuals, resulting in adverse effects on body condition of visiting birds. We tested the effects of sugar water feeding in urban New Zealand backyards by sampling target species for multiple infections and comparing bird body condition. For this, we compared backyards with and without sugar water feeders and again compared existing sugar water feeders with various sugar concentrations in two cities and in two seasons. Birds caught in gardens with sugar water feeders had poorer body condition; however, birds had better body condition in the city with the warmer climate (Auckland), during summer, and in gardens with high (≥20%) sugar concentration in sugar water feeders in winter. All screening tests for Chlamydia psittaci and Salmonella spp. returned negative results. Avian poxvirus prevalence in tauhou ( Zosterops lateralis) was four times higher in the city with a warmer climate. The likelihood of lice infection in tauhou was lower in gardens with feeders, in the warmer city, in summer, and at feeders with higher sugar concentrations. In tūī ( Prosthemadera novaeseelandiae), the likelihood of lice infection decreased with an increase in sugar concentration. Coccidia infection was 4.25 times higher in tauhou in gardens with feeders. Despite the identified risks associated with sugar water feeding, there appear to be potential benefits for native nectarivorous birds, specifically in winter.

Feeding backyard birds with sugar water is increasingly popular in urban areas, but it has poorly understood effects on bird assemblages. In New Zealand, ca. 20% of households engaged in feeding wild birds use sugar water, often in an attempt to attract native, nectarivorous birds. Developing best practices for sugar water feeding could be a powerful tool for attracting these species in urban areas. However, it is currently unclear whether these feeders actually support native species, and, if so, which feeding practices are most effective in increasing visitation. We surveyed New Zealanders who provide sugar water to birds about their feeding practices via an online questionnaire. The aim of our research was to understand existing practices and their effect on attracting native species, as well as the motivations and social factors behind urban sugar water bird feeding. Our results show that this practice is popular throughout the country with the majority of households successful in attracting native nectarivorous species to their gardens. Sugar water feeder type had the largest effect on reported species richness at feeders in comparison to other factors (e.g. sugar concentration). Feeders specifically designed for nectarivorous birds, namely the Tui Nectar Feeder™, are more successful at attracting natives in comparison to other commonly used feeder types. Thus, individual householder decisions around feeder use can have important consequences for bird species composition in urban gardens. Future research is needed to understand the consequences of sugar water feeding for bird communities and individual bird health.