Photoperiod and rainfall are associated with seasonal shifts in social structure in a songbird

Abstract

Seasonally breeding animals often exhibit different social structures during non-breeding and breeding periods that coincide with seasonal environmental variation and resource abundance. However, we know little about the environmental factors associated with when seasonal shifts in social structure occur. This lack of knowledge contrasts with our well-defined knowledge of the environmental cues that trigger a shift to breeding physiology in seasonally breeding species. Here, we identified some of the main environmental factors associated with seasonal shifts in social structure and initiation of breeding in the red-backed fairywren (Malurus melanocephalus), an Australian songbird. Social network analyses revealed that social groups, which are highly territorial during the breeding season, interact in social “communities” on larger home ranges during the non-breeding season. Encounter rates among non-breeding groups were related to photoperiod and rainfall, with shifting photoperiod and increased rainfall associated with a shift toward territorial breeding social structure characterized by reductions in home range size and fewer encounters among non-breeding social groups. Similarly, onset of breeding was highly seasonal and was also associated with non-breeding season rainfall, with greater rainfall leading to earlier breeding. These findings reveal that for some species, the environmental factors associated with the timing of shifts in social structure across seasonal boundaries can be similar to those that determine timing of breeding. This study increases our understanding of the environmental factors associated with seasonal variation in social structure and how the timing of these shifts may respond to changing climates.

Plural breeding among unrelated females and other insights on complex social structure in the cooperatively breeding Variegated Fairywren

“…2a). A few groups were isolated from the rest of the population, likely due to geographic boundaries (Welklin et al . 2023).…”

Complex relationships between climate and reproduction in a resident montane bird

“…We conducted sliding window analyses to test which climate variables best-predicted variation in timing of breeding and reproductive performance across years [ 13 , 18 , 27 , 61 – 63 ]. We ran separate sliding window analyses for each combination of climate and breeding variables to determine the climatic periods associated with variation in each breeding variable [ 61 ].…”

“…Therefore, we tested whether our top windows performed better than what would be expected by chance by comparing the improvement of our top model for each climate variable over the null model (ΔAICc) to the ΔAICc of 100 randomizations for each breeding variable [ 65 ]. We randomized our observed data by reassigning data from a single year to the same random year, but the climate data were kept matching their original year [ 27 ]. This randomization process keeps sets of yearly breeding values together rather than randomly mixing breeding values across years, which would eliminate the variation between years that is inherent to this type of data.…”

“…However, temperature may not be the most reliable predictor of breeding phenology in all ecosystems or for all species, as the effects of climate change vary widely across environments and are not limited to changes in temperature [ 24 ]. For example, in the tropics, where precipitation may be a more important driver of insect abundance than temperature, rainfall is often the primary environmental cue associated with the start of breeding [ 25 – 27 ]. Understanding how animals in different environments respond to variation in different climatic conditions is critical to predicting how animal populations may respond to the many facets of global climate change.…”

Ecogeography of group size suggests differences in drivers of sociality among cooperatively breeding fairywrens

“…Fairywrens present an ideal system for examining intraspecific variation in group size because (i) all species exhibit some degree of cooperative breeding, (ii) they are well studied and thus we have a good understanding of the benefits of cooperation across various species, and (iii) many species range over a variety of climates. Further, climate has been tied to reproductive success in this family, with rainfall positively predicting nest initiation, clutch size, and reproductive success [23][24][25][26][27][28][29][30], probably because of the positive correlation between precipitation and resource availability (e.g. insect availability; [28,31,32]).…”