Life history and population dynamics of the African Pygmy Falcon - an obligate associate of the Sociable Weaver

Olubodun, Olufemi

Life history and population dynamics of the African Pygmy Falcon - an obligate associate of the Sociable Weaver

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Department of Biological Sciences

Faculty

Faculty of Science

Abstract

Raptors play key roles in nature from providing key ecosystem services to serving as flagship species for conservation initiatives. As apex predators and scavengers, raptors can control prey populations directly and indirectly thus maintaining delicate ecosystem balance, potentially controlling pest and disease spread. Raptors have a slow life history and are long-lived hence are more sensitive and reflective of long-term anthropogenic-driven changes than other avian groups. Desert-living raptors are even more prone to anthropogenic changes, particularly climate change as they already exist in environments that often nearly reach their ecological thresholds. These make raptors key conservation flagship species and important surrogates for studying the effects of changing climate. Despite these roles and their vulnerability to environmental pressures, research into the life-history and ecology of this avian group is limited, notably for African species inhabiting arid environments. Existing knowledge often focused on large charismatic species, with little research on small-sized species. I aim to understand and unravel the life history and ecology of a desert-dwelling raptor and how these are impacted by meteorological variables. In this thesis, I focus on the ecology of the African pygmy falcon (Polihierax semitorquatus) – Africa's smallest diurnal raptor, for which until now little information exists. This desert-dwelling species inhabits the Kalahari Desert of southern Africa where the weather is already at extreme levels and predicted to become more severe due to climate change. As a predator and obligate nesting associate of sociable weaver (Philetairus socius) colonies which serve as a microecosystem for fauna and flora interaction, the falcon can potentially structure the local ecosystem. Previous study on pygmy falcons show that they induce direct and indirect impact on their nest host and other associates of the nest. An initial study on their breeding biology was descriptive and a more recent study have established their cooperative breeding strategy. The main aim of this PhD was to investigate the life history and population dynamics of pygmy falcons and how these respond to metrological variables using long-term life history and demographic data collected from 2011 – 2024. I began by exploring the annual population density and variation in the reproductive traits of pygmy falcons. I found significant annual variation in clutch size, number of fledglings produced and likelihood of successful breeding. Second, I aimed to understand the breeding phenology of the falcons and the relationship with rainfall and temperature. I found strong negative association between clutch initiation date, and body condition of chicks with temperature. However, rainfall was more important for breeding success, and these followed a positive association. Third, relying on initial studies on population abundance of the pygmy falcons and effect of group living on their fledging conditions, I investigated the effect of rainfall, temperature, and group living on the survival of pygmy falcons. The results indicated no annual variation in survival, weak effects of winter and summer temperatures on adult survival, and no weather signals for juvenile survival. Finally, I considered delineating the home range size and explore the daily activity patterns of pygmy falcons. I investigated the latter in relation to time of day and temperature. I achieved this by attaching miniaturized GPS tags as backpacks on the falcons for a two-week duration during their chick-rearing phase. I found temperature thresholds important for limiting pygmy falcons' activities. Clearly, temperature at certain thresholds imposed limits on the activities of pygmy falcons prompting behavioural changes to optimize thermoregulation. I concluded that the year-to-year variation in the breeding parameters of pygmy falcon in my study population is likely linked to the high annual environmental stochasticity. Weather variables were more important for phenological traits, and daily activities, than for vital rates like survival, suggesting differential vulnerability of life stages to environmental pressures. As climate change is predicted to become more severe, with desert temperatures expected to become more extreme, pygmy falcons could experience severe phenological limitations. Moreso, the lack of effect of weather on survival may suggest that they are driven by other anthropogenic changes or intrinsic traits not considered in this thesis.

Keywords

raptors

african pygmy falcon

Reference:

Collections

PhD / Doctoral

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