Avian breeding phenology and functional traits in relation to climatic variation
thesisposted on 2022-03-28, 10:02 authored by Daisy Englert Duursma
The goal of this thesis is to explore how adaptations modulate the influence of climatic extremes in breeding birds. I develop novel methods to collate and analyse breeding observations from conventional and non-conventional data sources and compile the largest dataset of avian breeding observations in Australia. I assess spatial and temporal patterns of breeding phenology for approximately 330 species to evaluate how phenology varies across five biomes, (based on a national classification system where the tropical and equatorial regions were combined). Arising from this was the novel finding that birds in the desert breed significantly earlier than in any other biome. Additionally, phenology calculated from single sightings of juvenile birds or eggs was interchangeable with multi-visit observations,increasing the breadth of data available for breeding-time studies. I tackle a longstanding ecological question about which climatic conditions underpin the timing of opportunistic breeding. I show that inter- and intra-specific breeding niches differ systematically across tropical, subtropical, grassland, desert, and temperate biomes,and over temperature and aridity gradients. A key finding is that hot temperatures constrain breeding in arid regions, but the effect of rainfall is not as universal as commonly assumed. I further examine the relationship between breeding and climate, exploring variation in phenology in relation to the El Niño-Southern Oscillation (ENSO). Australian birds breed for longer and with greater intensity during the La Niña phase of ENSO, providing an outstanding opportunity for well-timed conservation initiatives. Finally, I demonstrate that the distribution of egg shape and nest types reflects selective pressures of critical environmental parameters such as temperature and the drying capacity of the air. In hot/dry areas with sparse plant canopies, mean egg elongation decreased, and the proportion of species with covered nests increased. Predicting which species may cope with extreme climate from measurable phenology, climatic niches and traits provide a timely solution for assessing vulnerability from climate change.