A very exciting new research tool that is emerging, is our ability to track birds by satellite or geolocator. In the case of the Eurasian Hobby, the first four birds that pioneered this tremendous technology were tracked carefully by GPS while on their migratory journeys in 2005 – 2007. Their routes are depicted on the map at right. These birds cruised all the way from from Sweden to Angola and Zambia. Out of the 61 days that their journey on the way to their wintering quarters took, 39 days were spent travelling. Between the birds, the average distance traversed was 9,200 km. The mean travel speed in Europe was a relatively leisurely 188 km/day. However, for the four days it took the birds to cross the inhospitable Sahara, their speed was more than doubled (391 km/day). The passing over tropical Africa was performed at a speed of 200 km/day (Strandberg et al. 2009b). Hobbies fly between 7,9 to 14,6 hours daily, moving a maximum of about 1,250 km in just 2 days, with some migration at night (Orta and Kirwan 2014). The falcons crossed the Mediterranean Sea on a broad front, unlike soaring raptors like eagles and buzzards that concentrate at migration bottlenecks because of their dependence on thermals; consequently they show up in high numbers over Gibraltar in the west and along the eastern coast of the Mediterranean where the difference in temperature between land an sea allows them to take advantage of the raising air.
ABOVE: Migration routes of four different hobbies (from Strandberg et al. 2009a) showing the crossing of the Mediterranean Sea south of France and Italy, the fast crossing of the Sahara, the latitudinal spreading in western Africa, funneling through to cross the rainforest area and movements in the wintering area in Angola, Zambia and northern Namibia and Botswana.
Travelling south on individual routes that spread out from each other more than 2,000 km north of the equator, all the tracked Eurasian Hobbies converged to cross the evergreen tropical rainforest in the Congo on tracks not further apart than 70 km. Here the extension of the rainforest is shortest from north and south. For more details on travel schedules, migration routes, the rainforest as a possible ecological barrier and the discussion of the findings, see Strandberg et al. (2009a). Similar migration routes were confirmed in a later study (Meyburg et al. 2011), which added data that Eurasian Hobbies, which spend the winter in Angola, undertake huge latitudinal flights. One bird flew from Angola through Zambia, Zimbabwe and Botswana back to Namibia in less than three weeks, while the movement in Angola alone covered an area of about 116 000 square km, an area three times the size of Switzerland (Meyburg 2013).
Travelling the world (and crossing the Indian Ocean?)
Hobbies are true globetrotters, and not averse to a bit of exploring. In addition to their normal breeding, non-breeding and migrational range, there are many documented occurrences of vagrancy in areas far beyond their ususal limits. Some birds apparently disperse over all oceans and reach islands far off the north and west of Europe and even islands off Alaska. The species has also been recorded in the Southern Seas on islands in the Indian Ocean, off Indonesia, Australia and on tropical Pacific islands. Two records are mentioned for the USA and two for Canada (in both countries, from the east as well in the west; Orta and Kirwan 2014; Glutz von Blotzheim et al. 1971) and a review in the Encyclopedia of Life shows even more sightings and collected specimens on the North American continent (see their website in the literature list).
This raises the question of whether eastern populations of Eurasian Hobbies wander across the Indian Ocean, from India to East Africa for the non-breeding season, like the related Amur Falcons Falco amurensis do in great numbers during migration. An interesting parallel between these two species, is that they both feed on species of dragonfly called the Globe Skimmer Pantala flavescens. This large dragonfly, in a transgenerational cycle, undertakes a migration from India to Africa and back, as described further below. While Ferguson-Lees (2001) considers a Indian Ocean crossing by the Eurasian Hobby to be a possibility, this seems unlikely considering the low numbers of observation records. For example, the Eurasian Hobby is regarded as a scarce winter visitor to the Maldives (Naoroji 2006), while for the Seychelles overall only 28 records have been recognized (Safford and Hawkins 2013). Bijlsma (pers. comm.) pointed out that there are no records of hobbies fattening up in India before crossing the Indian Ocean (accumulating fat reserves to act as fuel for long flights during their trans-oceanic migration), unlike Amur Falcons.
I bless the rains down in Africa .
What do hobbies do on their African summer holiday? Eurasian Hobbies mainly arrive in Africa from late October to November, and in the southern parts of their range as late as December. Such a late arrival date is probably scheduled in order to allow time for the spring rains to promote the development of abundant vegetation – and consequently an abundance of insects. Departure back towards the breeding grounds starts from the end of February, and the northerly breeding grounds are reached in April and May. In ten years of data collection for the South African Bird Atlas Project 1 (SABAP 1) from 1987 to 1997, a total of only 1,384 Eurasian Hobbies were recorded in the South Africa, Namibia, Zimbabwe and Botswana, corresponding to 12,1% of southern Africa’s quarter degree grid cells. This species is considered generally uncommon here, and is most frequently reported from northern Namibia and Botswana, Zimbabwe, the northern and eastern ‘Transvaal’ (nowadays Limpopo and Mpumalanga, respectively) and Swaziland. In well-atlased areas it has been observed sporadically along the eastern and southern coasts, and even reaching Cape Town on occasion (Mendelsohn in Harrison et al. 1997). For retrap data and tracking migration movements in individual birds in Europe see Glutz von Blotzheim et al. (1971).
ABOVE: Distribution map of Eurasian Hobby in southern Africa based on SABAP 1 data. The species is clearly more common in the northern parts of the subregion, and especially the woodland and savanna belt of northern Namibia, Botswana and Zimbabwe. It is scarce but widespread in South Africa, as indicated by the yellow squares. Source: SABAP2 website.
ABOVE: SABAP2 distribution map of the Eurasian Hobby in southern Africa (note that coverage for countries neighbouring South Africa is incomplete). The apparent abundance around urban centres such as Gauteng, Durban and Port Elizabeth is probably just a reflection of the fact that there are more birders on the lookout in these areas. The Kruger National Park, running along South Africa’s north-east border is an important area for this species (as for many, many other raptors). The approximate borders of the park can almost be deduced by the density of hobby records. Note the scattered records from dry interior of South Africa. Source: SABAP2 website.
Birds, bats, insects: all you can eat
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.
Dragonflies – snacks from Asia
While ringing in Namibia, we found numerous dragonflies as bycatch in our mist-nets on a daily basis. These were mainly the Globe Skimmer Pantala flavescens, also called Pantala, Globe Wanderer or Wandering Glider; as well as some Blue Emperors Anax imperator. The 5 cm long Globe Skimmer is a spectacular species, and is well worth googling. Better yet, check out this astonishing TEDtalk by Charles Anderson. Its life cycle story starts when, incredibly, it crosses the Indian Ocean during the rainy season with the monsoon shifts from India. It then breeds in equatorial East Africa (October/November). The next (second generation) moves into southern Africa in December to February, while the newly hatched third generation returns in a northern direction to East Africa. Finally, the fourth generation moves with the (now east-blowing) monsoon winds back to India in June/July. In this circuit across the Indian Ocean, four generations of Pantala flavescens cover a distance of 14 000 – 18 000 km (Anderson 2009). A paper on stable isotopes even points out the probability of this dragonfly species coming from northern India, possibly from north of the Himalaya, which would prolong the circuit to a still unknown distance (Hobson et al. 2012).
This migration pattern is possible through the extraordinary short larval life of Pantala flavescens of 38 – 65 days (Suhling et al. 2004), which allows this dragonfly species to breed in ephemeral freshwater pools after rainfall (Silsby 2001). Using all surface water for short term breeding, in one year, three or even four generations can be produced (Johansson and Suhling 2004). Most dragonflies live the greatest proportion of their lives as larvae underwater, where they spend months or even up to two years, before they turn into aerial insects. In this state they survive only 6-9 weeks, or at most a few months as airborne insects. The Globe Skimmer is the dragonfly with greatest range worldwide. Incredibly, it has been recorded at an altitude of about 6,200 m in the Himalyas. Occurring even on small islands very distant from the mainland, it was one of the first species to resettle on the Bikini Atoll after the destruction by nuclear tests (Silsby 2001).