HMN 2026: How GPS tracking reveals pygmy falcons use less than 1 km² to raise nestlings

A new study, published in the Journal of Raptor Research, reveals that Africa’s smallest diurnal bird of prey, the pygmy falcon (Polihierax semitorquatus), operates within one of the smallest breeding home ranges ever recorded for a raptor.

The study was led by researchers from the University of Cape Town, with collaborators at Hartpury University and the Forest Science and Technology Center of Catalonia. Using ultra-light GPS tracking technology, researchers found that these birds require less than 1 km² to raise their young, challenging long-held assumptions about the spatial needs of predatory birds.

A defining characteristic of the pygmy falcon’s ecology is its unusual nesting strategy. Unlike most raptors that construct their own nests, the pygmy falcon depends entirely on the nests constructed by the sociable weaver (Philetairus socius). They roost and breed in chambers within the massive, multigenerational communal haystack nest, coexisting with the weavers at these nests and effectively anchoring their activities around a weaver colony.

Tracking a tiny hunter

To capture this fine-scale movement, the research team deployed miniaturized GPS tags weighing less than 2 grams on 13 adult pygmy falcons at Tswalu Kalahari, a private reserve in South Africa. The tags were manufactured by Pathtrack Ltd. Because the falcons weigh only about 56 grams, such studies were historically impossible until recent breakthroughs in technology.

The data, comprising nearly 4,000 GPS locations, showed that during the chick-rearing phase, the falcons used an average area of just 0.93 km². This is approximately 14 times smaller than the home range of the lesser kestrel, previously one of the smallest GPS-tracked raptors.

Conservation at a finer scale

The findings suggest that conservation strategies modeled after wide-ranging “umbrella species,” such as eagles or vultures, may not fully capture the ecological requirements of smaller predators.

“This study provides a crucial baseline for understanding the spatial requirements of small raptors, which have been largely overlooked due to technological limitations,” said lead author Dr. Olufemi Olubodun, Carnegie Postdoctoral Fellow at the FitzPatrick Institute of African Ornithology (Fitz).

“While wide-ranging raptors are often used as surrogates for broad-scale conservation plans, species with smaller home ranges may complement this role by reflecting ecological processes operating at finer spatial scales.”

Shared parenting in flight

The study also revealed a surprising lack of sexual dimorphism in movement. While female raptors are typically larger and often exhibit different movement patterns than males, both male and female pygmy falcons used similar-sized home ranges. This suggests “a high degree of shared parental responsibility during the critical period of chick-rearing,” said senior author Associate Professor Robert Thomson, also from the Fitz.

“Small raptors have been underrepresented in movement ecology. Now, with advances in technology, we can begin to understand their ecology in the same detail as larger species.”

Breeding season limits the picture

The researchers note that while these findings are definitive for the breeding season, further study is required to determine how these home ranges shift during the nonbreeding months, when the birds are not tethered to the weaver colonies to raise nestlings.

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