Seasonality and dietary diversity in flower and fruit consumption by birds: long-term dataset from a New Zealand wildlife reserve

Seasonal dynamics shape the timing and intensity of bird-plant interactions but are increasingly altered due to anthropogenic disturbances such as biodiversity loss and climate change. Baseline data on these patterns are critical, especially for restored communities where threatened bird species act as both pollinators and seed dispersers. We documented bird-plant interactions in Zealandia ecosanctuary, New Zealand, over nine years and investigated seasonal patterns in the timing, duration, and rate of avian visits to flowers and fruits at both the community and individual plant species levels. Additionally, we compared the dietary diversity of the avian community and the evenness with which different species consumed flowers and fruits. During 568 hours of sampling between 2006 and 2015, we observed 1327 flower visits and 2886 fruit visits involving eight native bird species and 25 native plant species. Flower visitation peaked in October (austral spring), while fruit visitation peaked in April (austral autumn). Seven bird species visited the flowers of ten plant species, with Fuchsia excorticata having the highest visitation rate (16.4 visits per hour). Eight bird species consumed the fruit of 20 plant species, with Coprosma robusta (8.6 visits per hour) and Geniostoma ligustrifolium (8.1 visits per hour) being the most visited. Visits were temporally staggered among plant species for both flowers and fruits. Fruits that were visited mid-season and flowers with high visitation rates had the broadest temporal spreads of visits. Fruits had a more even distribution of visits than flowers, indicating a broad exploitation of fruit resources compared to a more specialised use of floral resources. Our findings reveal strong seasonal partitioning of bird-plant interactions, with distinct and staggered peaks in flower and fruit visitation that likely reflect resource availability. This seasonal partitioning indicates that birds track seasonal resource shifts to sustain year-round foraging. These results provide long-term baseline data for a restored community of threatened mutualists, offering a reference point for detecting and managing future shifts under environmental change.