Data supporting "Breeding biology of the Karoo Prinia Prinia maculosa"

A detailed study on breeding biology of the Karoo Prinia (Prinia Maculosa). Datasheets include metadata describing each sheet. Datasheets are Days_to_first_egg: number of days from completion of nest-building until first egg laid. Faecal sac disposal: Details of whether faecal sacs removed at video-recorded nests. Feeding nestlings: Details of feeding of nestlings by parents at video-recorded nests. Females incubating eggs: Details of incubation of eggs at video-recorded nests. Fluff to nest: Details of whether fluff brought to video-recorded nests. Incubating nestlings: Details of incubation of nestlings at video-recorded nests. Male feeding incubating F: Details of males visits to video-recorded nests where females were incubating, including instances of males feeding the incubating female. Male Territorial calling: details and durations of male territorial calls. Morphometrics: Details of morphology (mass, wing length etc.) of male and female birds caught by mist-netting. Nestling growth rates: Details of nestling growth rates from hatching to fledging. Nests_by_month_all_years: Details of dates when the first egg of each clutch was laid across all Karoo Prinia nests during 2014–2020 (months divided into three sections: days 1–10, 11–20, and 21–30/31). Prinia Egg sizes: Egg sizes of all measured prinia eggs. Prinia_nest_heights: Heights above ground level of all prinia nests. Prinia nest orientations: Orientation (secondary intercardinal directions) of each prinia nest, determined as direction the entrance hole of the nest was facing. Rainfall history: Details of rainfall at the study site. Territory sizes: Sizes of measured territories of Prinia pairs. Methods: The study was conducted from 2014 to 2021 in a 120 ha area along a 4 km-stretch of gravel road north of Botrivier town, Western Cape, South Africa (34°13’S, 19°12°E; Supplementary Figure 1). Some additional observations (up to 2025), including during the non-breeding season, were made on Restanwold Farm in Elgin (34°13'S, 19°03'E), 13.5 km west of the study site. The main study area is a mosaic of agriculture (vineyards, annual grain crops, and grazing), Western Rûens Shale Renosterveld, and Kogelberg Sandstone Fynbos (Rutherford et al. 2006). These relatively short, open vegetation types are invaded, especially along the Bot River, by taller, introduced acacias (Acacia longifolia, A. cyclops, A. pycnantha, A. melanoxylon), gums (Eucalyptus lehmannii), and scattered pine trees (Pinus spp.) (Supplementary Figure 2). Most observations were conducted from mid-July to late December to coincide with the Karoo Prinia’s main breeding season (Dean 2005). Occasional visits were made in the non-breeding season, and year-round observations were made at the Elgin site. Adult Karoo Prinias were mist-netted and given individual colour ring combinations. Sex was confirmed in several cases by observing copulation and subsequently by other behavioural differences determined during the study (e.g. territorial calls were unique to males). Mass was measured with a Pesola PPS200 digital scale to the nearest 0.01 g, with birds constrained in a tube. Wing and tail were measured with a wing rule to the nearest 1 mm, and Vernier callipers were used to measure tarsus, culmen (beak tip to feather line on head), and head (tip of beak to back of head) to the nearest 0.1 mm. Nestlings were ringed at roughly 8–9 days old. Nests were found by observing birds carrying nesting material (grass or fluffy nest lining) and by following birds with bent tails (some females developed bent tails while sitting in the enclosed nest). For each located nest, we assigned a number (year followed by territory ID, which remained constant across years) and recorded GPS coordinates, plant species, height above ground, orientation of nest entrance, and a qualitative measure of the level of concealment. We noted whether nests were well concealed and constructed near the centre of a plant, well-hidden near the edge of the plant, visible on the side or top of the plant, or in sparse plants with little cover. Note that sample sizes differ across different datasets as not all measurements were taken in all years or for all nests. Eggs or nestlings were removed from nests between 08:00 and 09:00 to be weighed and photographed, then replaced in the nest with minimal disturbance. The length and maximum width of each egg was measured to the nearest 0.1 mm with Vernier callipers and photographed with a Canon EOS camera against a standard grey background. Nestlings were weighed with a Pesola digital scale to the nearest 0.01 g and photographed on a 5 mm grid background. Older chicks (>6 days) were restrained in a cardboard tube for weighing. Chicks were rarely weighed close to fledging as they were difficult to return to the nest (c.f. Rowan and Broekhuysen 1962). When disturbed, nearly-fledged chicks jump from the nest and scrabble speedily through the vegetation, hiding in the undergrowth. Parents continued to feed these chicks and, on the few occasions when this occurred, the chicks survived. Video cameras (Canon Legria HFR806 HD) were used to record vocalizations and behaviours at the nest, particularly during egg-laying. Cameras were housed in camouflaged wooden boxes tied to natural vegetation or wooden droppers 1–3 m from nests. Once the first egg was laid, recording was started around sunrise and left running for 3–4 hours. This was repeated daily until clutch completion. Video footage allowed us to determine the start of incubation (i.e. when the female first started sitting on the eggs for more than a few minutes at a time), the duration of incubation sessions, and male visits to feed the female in the nest. Deploying or recovering cameras disturbed birds, so we only recorded behaviours relating to incubation or brooding nestlings once a bird had returned to the nest after camera deployment, and stopped recording behaviours on the last occasion a bird visited the nest (excluding times when it left due to an observer approaching to recover the camera). Incubation durations were estimated from the time an individual entered the nest until it left, and foraging durations from exiting to again entering the nest. For estimations of feeding rates, the full recording session was used as short visits with prey were not interrupted by observers deploying or recovering cameras. At some nests, a small (15 mm) Handykam video camera was inserted through a small hole made in the top of the nest to record feeding, chick vocalizations, and brooding frequency. Extra vegetation to conceal the equipment was gradually placed on top of the nest during incubation before the camera was deployed. The camera was attached to a 12V battery and Handykam monitor placed on the ground 2–3 m from the nest (well-hidden and camouflaged). Cables were covered in grass and vegetation to make them less visible.