Proceedings of the Vertebrate Pest Conference

American barn owls (Tyto furcata; hereafter barn owls) are commonly attracted to breed on California farms for Integrated Pest Management; however, nesting barn owls face threats from the accelerating frequency and severity of heatwaves. Previous research has shown that the upper limit of a barn owl’s thermal neutral zone is 32°C (90°F) (Thouzeau et al. 1999). Negative effects of extreme temperatures on avian taxa include stunted nestling growth (Salaberria et al. 2014), delayed fledging (Cunningham et al. 2013), dehydration (Salaberria et al. 2014), hyperthermia (Thouzeau et al. 1999), and death (Hindmarch and Clegg 2024). We compared temperatures between two commonly used nest box designs to investigate heat mitigating attributes of size and shade panels. This study took place on a vineyard in the Central Valley of California, USA, with a Mediterranean climate where temperatures regularly rise above 38°C (100°F) in the summer (Table 1). The two box designs are freely available online. The smaller (hereafter, small) nest box’s dimensions are 57.8 × 40.6 × 31.4 cm (22.75" × 16" × 12.375") with a volume of 11,443 cm3 (4,505 in3). The larger (hereafter, large) nest box’s dimensions including the shades are 76.2 × 78.7 × 52.7 cm (30" × 31" × 20.75"), and without shades are 61 × 61 × 45.7 cm (24" × 24" × 18") with a volume of 26,334.7 cm3 (10,368 in3). We used Maxim Integrated iButtons (models: DS1921G, DS1923; Analog Devices, Inc., Wilmington, MA) to measure internal temperatures of the two nest box designs. Ambient temperature was extracted from an on-site weather station.