The great diversity of prey items taken by the Eurasian Hobby demonstrates the high adaptability of this species to available food sources. The diet consists of birds, terrestrial mammals (up to the size of a young rabbit), bats, insects, including dragonflies, beetles, moths, grasshoppers, locusts, crickets and ants, and some reptiles, depending on availability and the time in the life cycle (Orta and Kirwan 2014). Prey is mainly caught in flight, but also hunted from a perch, or even taken on the ground. Prey will be consumed on the perch or, in smaller prey items such as flying insects, it may be eaten on the wing. Some individuals specialize in certain prey types, especially when feeding young.
Kleptoparasitism has been observed, with Hobbies taking prey from other raptors like Rock Kestrel Falco tinnunculus, Sparrowhawk Accipiter nisus, Red-footed Falcon Falco vespertinus and Red Kite Milvus milvus and Black Kite Milvus migrans in flight (Fiuczynski and Sömmer 2011; Tinbergen 1958, p. 87-88). Conversely, hobbies themselves may also be robbed by other birds of prey.
In Europe at least 70 bird species have been recorded as prey of the Hobby (Glutz von Blotzheim et al. 1971). While raising its young, fledglings of other bird species are abundant, and these serve as food for the hobby’s offspring. Depending on availability, birds like swallows, martins and swifts, as well as less aerial species of open areas, e.g. sparrows, finches, starlings, larks and pipits are hunted. The main prey size is between 8 and 65 grams, with a range from small passerines of 6,5 gram up to lapwings or doves exceeding 200 gram (Bijlsma1980 in Fiuczynski and Sömmer 2011, p. 232 f.). A vagrant to Mahé, Seychelles was shot while feeding on a White Tern Gygis alba (Moreau 1938, p. 9). After rains hobbies have been observed taking advantage when swifts are handicapped by flying with wet plumage (Orta and Kirwan 2014).
Birds with eye-catching variation in shape and colour easily fall prey to the Eurasian Hobby. In well-studied breeding hobbies in the city of Berlin half of the prey consisted of House and Tree Sparrows, followed by different swallow and martin species. Astonishingly 9,4% of the food items were Australian Budgerigar Melopsittacus undulatus, escapees from cages (Fiuczynski and Sömmer 2011, p. 230), which were also reported as unexpected prey even in a large woodland areas in The Netherlands (Bijlsma, pers. comm.). One study shows that out of 215 House Sparrows 8,4% were partially leucistic (Bijlsma 1980 in Fiuczynski and Sömmer 2011, p. 236).
Astonishingly, 9.4% of the food items (in the city of Berlin) were Australian Budgerigars, escapees from cages
Many South African bird books describe the Eurasian Hobby as a hunter of dusk and dawn. Sighting the basic literature, it becomes clear that this assumption all funnels back to two articles on feeding behaviour of this species, one on the influence of raptors on bats, which are rarely diurnal (Fenton et al. 1994), and one on hobbies in the city of Stellenbosch, where the researcher could observe the birds only early morning before leaving and at nightfall coming back to the roost in town. Some bird nesting colonies in town were used as a food source at dawn and dusk, as well as occasional bats (Pepler 1993). The role of the scarcely observed diurnal hunting activity has thus largely been left out. The hobbies spent the day hunting and resting in the mountainous Fynbos, where their prey items included sunbirds, swallows, dragonflies, butterflies, even a flying ant and one unidentified nestling snatched out of the nest to be eaten on the wing.
It seems that the diet of Eurasian Hobbies on their African wintering grounds is composed in major parts of alates and insects which emerge in huge numbers after the rains (Orta and Kirwan 2014). Like other species, hobbies follow the insects being pushed in front of the rain clouds and sucked in by low pressure, and feed on alates emerging after rainfall. Travelling with the rain, individual Eurasian Hobbies can be seen in flocks of Red-footed Falcons and their eastern sister species, the Amur Falcon (M. Mills, pers. comm.). In northern Namibia, Hobby Falcons have been seen in the 70s in congregations of ‘dozens’ together with great numbers of raptors feeding on alates (Steve Braine, pers. comm.).
And how much do they actually eat?
The hunting strategy, feeding frequency and activity maxima are determined by the amount of food needed per day and depends not only on the kind of prey animals available, but also on individual preferences of the birds (Tinbergen 1958). Feeding times of up to 13 hours per day have been observed (Haverschmidt 1928; Schuyl et al. 1936). The daily food requirement is considered to be 15 – 17% (Bijlsma, pers. comm.) or up to 30 % of the body mass (Lit. in Fenton et al. 1994; Brown et al. 1982). An adult Eurasian Hobby would thus need 37,5 to 75 g of food per day. Two birds or bats of about 20 g would cover the minimum, while the same quantity by feeding on insects would require much more hunting time.