Toward Rapid Population Assessment for Raptor Conservation: Subadults, Floaters, Strawmen, and Context. A Response to Hunt and Law

Abstract

Many raptors exhibit life history characteristics that simultaneously place them at conservation risk and make them difficult to study, including delayed reproduction, long life spans, low annual fecundity, and large seasonal movements. Developing effective methods for rapid assessment of raptor populations will improve the feasibility and timeliness of adaptive management. To this end, we used a stage-structured demographic model to evaluate the insight into population decline risk provided by two population structure measurements: subadult nest occupancy and the ratio of non-territorial ‘‘floater’’ adults to territorial breeders (Monzón and Friedenberg 2018). Here, we respond to a commentary by Hunt and Law (2023) that addresses our study’s premises. There is no disagreement that the metrics require further context to be diagnostic; however, Hunt and Law (2023) offer three specific criticisms of our study, calling them strawmen. Although we did not intend them as such, discussing each criticism here offers an opportunity to clarify how these demographic metrics are and should be interpreted. First, Hunt and Law (2023) assert that we proposed, as a strawman, that subadult nest occupancy has only one possible explanation. They are referring to our summary of previously published work suggesting ‘‘a high incidence of subadults on nests might characterize a population in decline or at high risk of decline because it may be depleted of adult breeders and floaters’’ (Monzón and Friedenberg 2018, citing Balbontı́n et al. 2003 and Ferrer et al. 2003). Our summary reflects the preponderance of studies on the subject. Even Hunt and Law (2023), shortly after pointing out the narrowness of our summary, establish the general rarity of subadult nesting among raptors and assert that it should be regarded as a meaningful warning sign even if observed at a low level. With this premise as a hypothesis, we explored various ecological scenarios that can yield high rates of subadult nest occupancy and then assessed the value of this snapshot metric for indicating risk of population decline. The metric on its own was useful for identifying scenarios of moderate decline risk but failed to discern cases of low and high risk (Monzón and Friedenberg 2018). The examples presented by Hunt and Law (2023) all provide additional ecological context with which to interpret the metric properly and share the theme of high adult mortality being an important factor—the exact conclusion we reached in our original study (Monzón and Friedenberg 2018). In the example of Golden Eagles (Aquila chrysaetos) in the Altamont Pass Wind Resource Area in California, a high rate of subadult nest occupancy is interpreted in the context of high adult mortality from collisions with wind turbines (Wiens and Kolar 2021). Similarly, the