Using web-sourced photographs to examine temporal patterns in sex-specific diet of a highly sexually dimorphic raptor

Abstract

Traditional methods to study raptor diet are usually limited temporally, e.g. prey remains at nesting sites, and are unsuitable to examine dietary changes throughout the year. Using web-sourced photography, we explore temporal patterns in prey size and key prey species between sexes of the sexually dimorphic Eurasian sparrowhawk ( Accipiter nisus ) throughout the United Kingdom. We examined 666 photographs of sparrowhawk on prey and identified the prey species involved, together with sparrowhawk sex. Changes in prey size and proportions of key prey species over time (seasonally and monthly) were explored for each sex. Prey weight was substantially higher for females than males. However, on average, prey size for both sexes declined during the summer period (May–June) being the lowest in June, which is the main nestling-rearing month for both sparrowhawks and their prey. Compared with summer, rock doves ( Columba livia ) were more important prey for female sparrowhawk in winter. Whereas, for males, Eurasian blackbirds ( Turdus merula ) were more important in spring compared with autumn. Web-sourced photography can overcome several limitations of previous methods used to study raptor diet including the ability to quantify diet between the sexes throughout the entire year, however, may also introduce a prey-size bias toward larger prey items.

Continental scale dietary patterns in a New World raptor using web-sourced photographs

“…furcata ) diets found a positive relationship in the proportion of mammal prey in colder environments [ 25 ]. Unlike previous studies which studied the diets of Eurasian Sparrowhawk and Martial Eagles [ 27 , 29 ], we did not find any age effects in the diet of caracaras which may be explained by their generalist nature and tendency to feed on carrion [ 47 , 67 ]. Eurasian Sparrowhawk are avian specialists [ 27 , 28 ] and age-related differences in diet may be more pronounced.…”

“…Our approach, like most methods to study raptor diets [ 8 , 71 ], has been shown to be potentially biased towards larger and more identifiable food items, e.g., mammals and birds, which require longer processing times [ 28 , 29 ]. Consequently, this food-size bias may partly explain why we detected low relative proportions of smaller prey groups, such as invertebrates (2.9%), plant material (0.7%) and amphibians (0.6%) within our photographs.…”

“…For example, it has been used to examine spatial differences in the diet of adult and non-adult Martial Eagles ( Polemaetus bellicosus ) throughout sub-Saharan Africa [ 27 ]. Studies have also explored sex- and age-related diet differences in the Eurasian Sparrowhawk ( Accipter nisus ) and explored changes in this species’ diet, between the sexes, throughout the entire year [ 28 , 29 ]. Previous research, using this approach, examined diet specialization of Tiny Hawks ( A .…”

“…However, the role of more traditional approaches to study raptor diets must not be underestimated as they provide vital data on cryptic species and those that can be challenging to study in the field, e.g., tropical forest raptors [ 31 ]. Despite this, web-sourced photography is a useful tool to study well-sampled species that inhabitant large geographic areas including open landscapes and those associated with human activities [ 28 , 29 ].…”

Status and distribution of an introduced population of European Goldfinches (Carduelis carduelis) in the western Great Lakes region of North America

“…The use of web-sourced photographs has recently been used to explore the diets of birds (Naude et al 2019;Panter and Amar 2021). This method may suffer from bias, such as being photos more likely to be taken along roadsides, in open habitats, or in lower vegetation levels, but it can provide insight into a time-and cost-effective manner (Berryman and Kirwan 2021;Panter and Amar 2022). Our compilation of natural food sources derived from media associated with records from eastern North America (Suppl.…”