Local Weather Explains Annual Variation In Northern Goshawk Reproduction In the Northern Great Basin, USA

ABSTRACT Weather is thought to influence raptor reproduction through effects on prey availability, condition of adults, and survival of nests and young; however, there are few long-term studies of the effects of weather on raptor reproduction. We investigated the effects of weather on Northern Goshawk (Accipiter gentilis; henceforth goshawk) breeding rate, productivity, and fledging date in south-central Idaho and northern Utah, USA. Using data from 42 territories where we found evidence of breeding attempts in ≥1 yr from 2011–2019, we analyzed breeding rates using 315 territory–season combinations, analyzed productivity for 134 breeding attempts, and analyzed fledging date for 118 breeding attempts. We examined 35 predictor variables from four categories: precipitation, temperature, wind, and snowpack. Of the variables we evaluated, April precipitation, previous year's April–July precipitation, April–May mean temperature, and March–May mean temperature were related to measures of goshawk reproduction. Greater April–July precipitation in the previous year and lower April precipitation in the current year were associated with higher breeding rates. Years with warmer average April–May temperatures were associated with increased goshawk productivity. Years with greater April–July precipitation during the previous year and lower mean March–May temperatures were associated with later fledging dates. Based on these relationships, we considered projected changes in weather in the northern Great Basin over the next 50 yr as a result of climate change (without directly accounting for habitat changes caused by climate change), and predicted that climate change will: (a) have no significant effect on goshawk breeding rate, (b) have a positive effect on goshawk productivity, and (c) cause a shift toward earlier goshawk breeding. Our results indicate that weather is significantly related to goshawk reproduction in the northern Great Basin, and we suggest that the relationship between raptor breeding and weather be further investigated to enable higher resolution predictions of how changes in the climate may influence their populations, particularly changes that may not have been captured by our study.

Phantom of the forest or successful citizen? Analysing how Northern Goshawks ( Accipiter gentilis ) cope with the urban environment

By 2040, roughly two-thirds of humanity are expected to live in urban areas. As cities expand, humans irreversibly transform natural ecosystems, creating both opportunities and challenges for wildlife. Here, we investigate how the Northern Goshawk ( Accipiter gentilis ) is adjusting to urban environments. We measured a variety of behavioural and ecological parameters in three urban and four rural study sites. City life appeared related to all parameters we measured. Urban female goshawks were overall 21.7 (CI 95% 5.13–130) times more likely to defend their nestlings from humans than rural females. Urban goshawks were 3.64 (CI 95% 2.05–6.66) times more likely to feed on pigeons and had diets exhibiting lower overall species richness and diversity. Urban females laid eggs 12.5 (CI 95% 7.12–17.4) days earlier than rural individuals and were 2.22 (CI 95% 0.984–4.73) times more likely to produce a brood of more than three nestlings. Nonetheless, urban goshawks suffered more from infections with the parasite Trichomonas gallinae , which was the second most common cause of mortality (14.6%), after collisions with windows (33.1%). In conclusion, although city life is associated with significant risks, goshawks appear to thrive in some urban environments, most likely as a result of high local availability of profitable pigeon prey. We conclude that the Northern Goshawk can be classified as an urban exploiter in parts of its distribution.

Did genetic lineage divergence or spatial environmental variance lead to global subspecies differentiation of northern goshawk (Accipiter gentilis)?

When a widely distributed species undergoes ecological or geological isolation, it tends to divide into subspecies. In general, subspecies differentiation is affected by environmental variance and genetic divergence. But the extent to which these two factors influence subspecies differentiation in species with different distribution ranges and modes of living, might be different. Despite having high breeding habitat fidelity, northern goshawk is a forest raptor that is widely dispersed. We investigated morphological traits in combination with the genetic background of northern goshawk individuals at a large global scale. We also collected genetic, palynological and climatic data to reveal what caused global subspecies differentiation in northern goshawk. Eurasian and North American subspecies populations are thought to have diverged approximately 660 000 years ago to undergo different evolutionary routes, which remarkably facilitated intercontinental subspecies differentiation through genetic lineage divergence. During the last glacial period (18 000 years ago) the different isolation levels of northern goshawk refugia on the continents caused genetic lineage divergences, which, however, are unlikely to have led to subspecies differentiation directly. Spatial environmental variance due to the wide distribution of northern goshawks made an important contribution to subspecies differentiation throughout continents.