Exploring the use of the South African nest record scheme to detect changes in phenology: a case study using four well represented species

Phenological changes are one of the most well recognised responses of organisms to climate change. The ability to detect phenological change often relies on long-term datasets, which are scarce in the Southern Hemisphere. As the adaptive capacity of species is highly variable, it is important to better understand how species in the Southern Hemisphere may respond to climate change through shifts in their annual cycles. Citizen science projects, like bird nest record schemes, offer valuable long-term data, although data heterogeneity can pose challenges, affecting their use in research. To investigate the suitability of the South African nest record scheme (SANRS) for estimating phenological shifts, we conducted a preliminary exploration of shifts in lay dates in four well-represented species. Firstly, we explore the composition of nest cards for each species, specifically the proportions of single- and multi-visit cards. Secondly, we explore the accuracy of single-visit cards for estimating lay dates compared to more accurate multi-visit cards. Lastly, we compared analytical approaches to test for possible shifts in lay dates. We found little differences for lay date estimates between single and multi-visit cards and our different models showed similar patterns of lay date shifts for all species. Three of our four species (African paradise flycatcher Terpsiphone viridis, cape turtle dove Streptopelia capicola, cape wagtail Motacilla capensis and laughing dove Spilopelia senegalensis) showed a shift toward later laying over the period 1950–1999. Although only based on a limited number of species, this consistent pattern towards later lay dates contrasts with the general trends found in the Northern Hemisphere for shifts toward earlier laying. The mechanisms driving these shifts is currently unclear, but in contrast to the Northern Hemisphere, in this region rainfall rather than temperature may have a stronger influence on avian breeding phenology. Our results highlight the potential of the South African Nest Record Scheme to detect shifts in laying dates, paving the way for more extensive studies of phenological changes, and the mechanisms involved, in the under-researched region.