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.

Complex coevolutionary relationships among competitors, predators, and prey have shaped taxa diversity, life history strategies, and even the avian migratory patterns we see today. Consequently, accurate documentation of prey selection is often critical for understanding these ecological and evolutionary processes. Conventional diet study methods lack the ability to document the diet of inconspicuous or difficult-to-study predators, such as those with large home ranges and those that move vast distances over short amounts of time, leaving gaps in our knowledge of trophic interactions in many systems. Migratory raptors represent one such group of predators where detailed diet studies have been logistically challenging. To address knowledge gaps in the foraging ecology of migrant raptors and provide a broadly applicable tool for the study of enigmatic predators, we developed a minimally invasive method to collect dietary information by swabbing beaks and talons of raptors to collect trace prey DNA. Using previously published COI primers, we were able to isolate and reference gene sequences in an open-access barcode database to identify prey to species. This method creates a novel avenue to use trace molecular evidence to study prey selection of migrating raptors and will ultimately lead to a better understanding of raptor migration ecology. In addition, this technique has broad applicability and can be used with any wildlife species where even trace amounts of prey debris remain on the exterior of the predator after feeding.

Due to the economically and environmentally beneficial rodent control services birds of prey (raptors) provide, many property owners in North America and around the world install artificial nest boxes to attract breeding populations of barn owls as part of an integrated pest management (IPM) strategy. However, anticoagulant rodenticides (ARs) and barn owl biocontrol are often concurrently used to limit damage from rodent pest species in agricultural ecosystems which could lead to secondary poisoning of these beneficial predators. Substantial global effort is currently underway to determine the efficacy and cost effectiveness of this IPM approach, while better defining the risk to barn owls from potential AR exposure. While these issues have received increased attention, there is little data describing the circumstances in which barn owls interact with AR compounds, as well as the potential sublethal effects of AR exposure in these settings that may hinder a barn owl’s ability to adequately control pests in agroecosystems. By incorporating research techniques that can relate AR application to barn owl diet, movement, development, and secondary AR exposure frequencies, we can begin to understand the nature of employing chemical and biological control together in an IPM program. To understand the interactions between ARs and barn owls in IPM, we propose that studies investigate the frequency and severity of secondary poisoning in barn owls that are providing biological control on farms.