1 1 2 3 2 4 5 3 6 7 4 8 9 5 10 11 6 12 13 7 14 Harriers 15 8 16 17 9 18 Skydancing through time 19 10 20 21 11 22 Text by Rob Simmons 23 12 24 Illustrations by John Simmons 25 13 26 27 Harriers... For some, they conjure up lazy days on a wind- 14 28 29 swept grassland, watching a lone marsh slowly 15 30 31 and buoyantly quartering the dips and hollows, meticu- 16 32 33 lously searching for and the unwary before 17 34 35 18 36 disappearing into the heat haze. 37 19 38 For others, a day in the Cape’s fynbos 39 20 40 may reveal a rare jewel, the stunning 41 21 42 jet-black-and-white Black Harrier, skydancing majestically 43 22 44 overhead before descending 45 23 46 47 into a protea-covered valley to search 24 48 49 for quail or mice. 25 50 51 Going further afield one can visit the 26 52 53 Scottish moors, where ‘harrier’ is a dirty word and the Hen 27 54 55 Harrier is pitted against the 28 56 57 gamekeeper’s gun; even further afield one can visit the 29 58 59 30 60 Diving, twisting and calling in their remarkable grasslands of where roosts of a thousand harriers 61 skydancing display, Black Harriers mark their ter- 31 62 ritories and simultaneously advertise to prospec- can boggle the mind. 63 tive mates. 32

wendy dennis  33 1 1 2 3 ccurring worldwide, har- museum specimens of this bird exist, 2 4 riers are elusive, a quality and to this day no body mass data have 5 adding to their mystique, been published. 3 6 for they are alone in the From mitochondrial DNA extracted 7 raptor world as being the from feather and blood samples we 4 8 Oonly genus in which polygyny – a male know that the Réunion Harrier differs 9 pairing with two or more mates – is by 1.5 per cent from its closest neigh- 5 10 regular. Three species – the Hen, bour, the , 11 Northern and Euro­pean Marsh harriers meaning that they diverged from one 6 12 – commonly practise polygyny, while another more than 760 000 years ago. 13 several others do so at lower levels. These species did not evolve from the 7 14 It is this trait that started me on a but diverged 15 harrier odyssey which led me in the from their closest cousin, the European 8 16 footsteps of great naturalists such as Marsh Harrier, about a million years 17 Eddie Balfour in Orkney and Frances ago. With only an estimated 72 pairs in 9 18 Hamerstrom in North America, and the world, the small, dark Réunion Despite the Black Harrier’s endemic status, it 19 found me finally and firmly on the Harrier is the world’s rarest. It is also the 10 20 African continent. My quest was not to remains one of the world’s least known harriers. only harrier adapted to foraging over 21 repeat what they had already uncov- forest rather than marshland or 11 22 ered, but to delve into other aspects of steppe. 23 harrier ecology (such as the polygyny), to explain why some The second ‘hidden’ species to emerge is the North American 12 24 females continue to pair with an already mated male and leave Northern Harrier. This species differs from the world’s most 25 fewer copies of themselves than they would with a monoga- common harrier, the , by 0.8 per cent, meaning it 13 26 mous male, and to understand first-hand why harriers in south- diverged only about 400 000 years ago. The third species pro- 27 ern climes lay fewer eggs and rear fewer offspring than their posed (but not proven by DNA since none could be extracted) is 14 28 northern cousins. the of . It is thought to be a good 29 At a more fundamental level I also wanted to have first crack species because it is resident on New Guinea, differs in plumage 15 30 at determining how many species of harrier there are in the from its nearest congener, the , and 31 world, and in the process clear up the confusion around the because island forms have all proven good species. The full tally 16 32 world’s five marsh harriers, all originally designated as subspe- of the world’s harriers now stands at 16 species and may increase 33 cies of the European Marsh Harrier. as other island forms are analysed. 17 34 Now, 20 years after the journey began, I am able to provide The affinity of the Black Harrier is surprising because its near- 35 some answers to those questions. So how many harriers are est living ancestor is not, as was expected, one of the current 18 36 there, do new species lurk around the world to frustrate or gal- ‘steppe’ harriers which visit from (that is, the Hen 37 vanise the globe-trotting birder, and why is polygyny so com- or Pallid). It is South America’s small Cinereous Harrier. The two 19 38 mon in this group? species diverged about 1.5-million years ago and as such the 39 Twenty-seven years ago the Dutch taxonomist Ebel Nieboer Black Harrier is the youngest of the ‘steppe’ harriers. It is an 20 40 proposed 10 species of harrier: from Europe and eastern interesting quirk of nature that the youngest harriers (such as 41 Russia, the Hen, European Marsh, Montagu’s and Pallid; from the Black) are frequently found alongside the oldest (such as the 21 42 the African continent, the African Marsh and Black harriers; African Marsh which is about 4.6-million years older) on each 43 from and the striking Pied Harrier; from continent. For example, the youngest harrier in Europe is the 22 44 the only tree-nesting species, the Spotted Harrier; European Marsh, which forages alongside Montagu’s, the spe- 45 and from South America, the Cinereous and Long-winged cies which gave rise to the entire marsh harrier group some 23 46 harriers. Fifteen years later three new species were added by 3.5-million years before present. Likewise, in South America, the 47 American researchers Dean Amadon and John Bull. They rec- cradle of harrier evolution, the ancestral Long-winged is also 24 48 ognised as full species the Madagascar/Réunion Harrier of the about 3.5-million years older than the Cinereous Harrier with 49 Islands, and the two marsh harriers in the east- which it shares foraging and nesting grounds in . For 25 50 ern hemisphere: the Eastern Marsh and Australasian Marsh harriers, therefore, the mixing of the old and the new is the rule, 51 harriers. (As a reflection of the uncertainty of the affinities of not the exception. 26 52 the Australian harriers, taxonomists there named the As for polygyny, most European biologists presume that this 53 Australasian Marsh Harrier Circus approximans, meaning rare mating system arises from an excess of females unable to 27 54 ‘approximately like other harriers’ and the Spotted Harrier find mates and thus forced into polygyny. However, sex ratios 55 Circus assimilis, meaning ‘similar to other harriers’ – names are not skewed in North America and yet polygyny is just as 28 56 that don’t fill one with much faith in the taxonomic proc- prevalent there. There is little doubt that polygyny is closely tied 57 ess.) to open habitats (many marsh-nesting species are polygynous 29 58 Now 12 years on, with the assistance of Professor Michael in relation to those that inhabit three-dimensional habitats) All marsh harriers, bar the newly recognised 59 Wink and his colleagues in the genetics labs of Heidelberg and diet – especially a diet of voles. Because vole populations Réunion Harrier, are found foraging over 30 60 University, we can reveal with more certainty yet another three reach higher levels in more northerly latitudes, one expects and reeds and open water, where they also breed. 61 ‘hidden’ species. We can also reveal the ancestry of southern does find more polygyny there. It is also more prevalent in the Whether they will survive man’s onslaught 31 62 Africa’s own endemic (and particularly tissue-shy) species, the two species which dominate northern latitudes – the Hen and on their wetland habitat remains uncertain. 63 Black Harrier. Blood samples from this species were only Northern harriers, and is more common during vole population Here a female African Marsh Harrier 32 obtained after more than a year’s search and many false trails, peaks than vole troughs among these species. tendstends toto herher young.young. following a request in Africa – & Birding in 1999. Almost no  J.J.J.J. BROOKBROOKSS/PHOTO/PHOTO ACCACCESSESS 33

38 HARRIERS africa – birds & birding OCTOBER/NOVEMBER 2000 HARRIERS 39 1 1 2 3 2 4 5 3 6 7 4 8 9 5 10 11 6 12 13 7 14 15 8 16 17 9 18 19 10 20 21 11 22 23 12 24 25 13 26 27 14 28 29 15 30 31 16 32 33 17 34 35 18 36 37 19 38 39 20 40 41 21 42 43 22 44 45 23 46 47 24 48 49 25 50 51 26 52 53 27 54 55 28 56 57 29 58 59 30 60 61 The increasingly rare African Marsh Harrier is 31 62 the smallest of the world’s six marsh harriers. 63 HPH PHOTOGRAPHY/PHOTO ACCESS 32

33 1 1 2 3 Scientific names of the harriers 2 4 mentioned in this article, 5 in alphabetical order: 3 6 7 African Marsh Harrier Circus ranivorus 4 8 Australasian Marsh Harrier C. approximans 9 5 Black Harrier C. maurus 10 Cinereous Harrier C. cinereus 11 6 12 Eastern Marsh Harrier C. spilonotus 13 European Marsh Harrier C. aeruginosus 7 14 Hen Harrier C. cyaneus 15 Long-winged Harrier C. buffoni 8 16 Madagascar Marsh Harrier C. macrosceles 17 Montagu’s Harrier C. pygargus 9 18 Northern Harrier C. hudsonius 19 C. macrourus 10 20 Pied Harrier C. melanoleucos 21 11 Réunion Harrier C. maillardi 22 Spotted Harrier C. assimilis 23 12 24 25 13 26 27 14 Left Montagu’s Harrier (young male shown here) is the smallest 28 and the only truly colonial nesting species of harrier. It is found 29 15 breeding and foraging over the grasslands and farmlands of 30 southern Europe and . Birds winter mainly in West Africa 31 16 and India, but a small number make it to southern Africa 32 33 each summer. 17 34 35 Below Male Montagu’s Harriers rarely visit the nest, and leave 18 36 incubation and chick-feeding duties entirely to the female. 37 19 38 39 20 40 41 21 albert froneman 42 43 22 44 rom studies of the mate choice of female harriers it ble to gather more food, but nestling growth rates were much areas and because of the close relationship between food and 45 appears that polygyny arises because some males are lower than in unmanipulated broods. But is this because there clutch size, this is sufficient to explain the lower clutches of 23 46 able to supply lots of voles to several females in was less food in the environment or is it because these south- tropical and subtropical species such as harriers. 47 sequence as they start to breed, yet they are unable to ern harriers were not working as hard to gather food (and sav- Studies of harriers, and particularly the polygynous ones, have 24 48 maintain an ever-increasing rate as each female’s ing themselves for future breeding)? also revealed the reasons why female raptors are larger than their 49 youngF hatch. Thus, while they can attract many females, only This is a difficult question to answer and has never been mates, and it has also highlighted the astonishing abilities of 25 50 the first becomes the favoured female and is able to rear most of assessed before. By comparing the time spent foraging by females to change the sex ratio of their brood according to cir- 51 her young. The others, having been deceived into expecting African birds with that spent by northern birds at the same cumstances. There is far more to learn about this unusual group 26 52 large food supplies from the male, rear their young virtually time of the breeding cycle, I found that African birds spent and I hope this article and our just-published book will stimulate 53 single-handed and raise fewer young than if they had chosen a about 29 per cent of their time foraging – exactly the same others to unravel more of the mystique of the harriers.  27 54 monogamous­ male. Rarely do food supplies in southern climes amount of time spent by northern birds. So they were working 55 reach the levels found in the Northern Hemisphere so polygyny as hard to find food. However, when I assessed the amount of 28 56 is rare to absent among the Southern Hemisphere’s harriers. prey caught for every hour of hunting, some remarkable differ- 57 The experiments with clutch size of African Marsh Harriers ences became apparent. The foraging yield of African birds was Rob Simmons and his 29 58 have revealed several traits that are common to northern spe- approximately half that of northern zone birds; thus, for every twin brother, John, have 59 cies – and one major difference. Like their northern cousins, hour of hunting, an African Marsh Harrier caught half the recently collaborated 30 60 African Marsh Harriers increase the number of eggs they lay amount of prey that its northern cousins did. On looking for on Harriers of the World: 61 when they are given extra food before laying. This suggests other evidence of this difference I found in four north/ south Their Behaviour and 31 62 immediately that there is some food constraint preventing comparisons of other raptors that the southern (tropical) spe- Ecology, published 63 them from laying clutches as large as northern-zone birds. This cies were also collecting about half the amount of food that by Oxford University 32 Press. was verified by giving some pairs more young to rear in order northern (temperate) species were collecting per unit time. to gauge their child-rearing abilities. Not only were they una- This means that food is less available in subtropical or tropical 33

42 HARRIERS africa – birds & birding OCTOBER/NOVEMBER 2000 HARRIERS 43