behaviour

heronunderwater African

The is a familiar throughout most of the Afrotropics, and its relatives are found in other tropical regions world- wide. adapt readily to human-modified and often become quite tolerant of human disturbance. Yet, despite their unique foraging mode and peculiar moult strategy, they are surprisingly poorly studied. Peter Ryan lifts the lid on these fascinating . >

TEXT & PHOTOGRAPHS PETER RYAN

54 african birdlife albert froneman may/june 2013 DARTERS 55 MARIETJIE FRONEMAN

The darters are a small group in and South-East Asia east to is derived from a Tupi word mean- swim efficiently but makes them parted, and the bill tips have tiny, swallow. This leaves the bird vul- above Freeing impaled of tropical freshwater birds allied to the Philippines and Sulawesi, and ing ‘devil bird’. Apparently the first rather clumsy out of water. backward-pointing serrations that nerable to kleptoparasites, with prey from their bill tips the and, more distantly, the A. novae- inhabitants of what is now Brazil One of the striking differences act like the barbs of a fishing hook Giant Kingfishers, gulls, and requires some skill, and to and . With fos- hollandiae from east of Wallace’s regarded the bird as an evil spirit of from cormorants is the darters’ to prevent prey from wriggling free. even other darters not being averse darters practice with sils dating back at least 18 million line in , and the woods. Whether this dubious long, dagger-like bill that lacks a Apparently a few very small prey to stealing a darter’s . When other items, such as this , they have been separated . reputation resulted in the birds’ pro- hooked tip. It resembles a ’s items are swallowed underwater, threatened, the darter’s usual re- piece of reed. This bird from the cormorants for quite some Compared to the cormorants, tection or persecution is unrecorded. bill, and indeed is used in much the but most are brought to the sur- sponse is to dive, often repeatedly. repeatedly tossed and time (perhaps as much as 40 million darters have far fewer and Like cormorants, darters are same fashion, spearing prey rather face where they are shaken free Large fish may be carried to the caught it for several years) and, given several marked dif- a much smaller global range, but foot-propelled divers that feed than grasping it. from the bill tip. This tricky opera- bank where they are less likely to minutes. ferences in structure and behaviour they are widespread in tropical mainly on fish, although they also An aspect of darters that has tion requires some practice. Ideally be stolen, and in some cases really from cormorants, there is wetlands and can be quite tolerant take , , and been well studied is their mor- the prey item is tossed into the air, well-sized fish have to be aban- opposite and previous little doubt that they are best of humans. They are well known to occasionally molluscs, small ter- phology. They have a distinctively deftly caught and swallowed head doned because they are too big to spread The dagger- treated as a separate . casual birders, probably at least in rapins and aquatic . They hinged joint between their eighth first. If it falls into the water, there swallow. I haven’t come across a case like bill has serrations There are distinct darter part because they are so distinctive have been recorded taking food and ninth neck vertebrae which, is often a frantic stab or even a with a darter, but cormorants and on its tip to reduce species in the Old and New in the water. When swimming, only when on land, using the bill like a coupled with powerful muscles in- series of rapid dives to attempt to have been recorded choking the chances of losing Worlds, with the form the bird’s head and neck protrudes pair of forceps to catch insects, and serted to special keels on vertebrae recapture it. Small fish, which are to death while trying to gulp down prey. Coupled with the Tnow generally regarded as com- above the surface, giving rise to the the American Darter has even been five to seven, allows them to shoot usually speared only by the upper too large a fish. powerful neck muscles, prising three allospecies: the common name of ‘snakebird’. reported to eat Celtis berries. Their their head forward in much the mandible, tend to be handled quite Spearing fish in the side typically it makes the bill a African Darter rufa in sub- The name Anhinga is also large feet have all four toes webbed, same manner as a heron or , easily, but larger prey can require requires a more subtle approach formidable weapon that Saharan Africa and , used as a common name for the and their legs are situated far back typically hitting their prey side-on. some effort to shake free, and even than chasing them down. Com- helps to deter would-be the A. melanogaster American Darter A. anhinga and on the body, which allows them to They strike with the bill slightly more time to orientate correctly to pared to cormorants, darters rely > predators.

56 african birdlife july/august 2013 DARTERS 57 They are able to hang motionless within centimetres of the water sur- face, waiting to ambush their prey

specialise in feeding in relatively shallow wetlands, but they can’t af- ford to kick frantically to remain in place when feeding. So they forego their insulation, and allow their to become fully saturated with water. This explains why darters sit so low in the water. Aided by their unusually dense bones and relatively small air sacs, they are close to being neutrally buoyant at the water sur- face. They are able to hang motion- less within centi­metres of the water surface, waiting to ambush their prey. They often lie in the water with their wings and tails partly spread. It has been suggested that this is to create pools of shade to attract small fish, much as a uses its above Darters often clamber out far more on stealth, moving slowly wings as an ‘umbrella’ to shade the of the water at the end of a for- through the water or waiting for water, but it almost certainly also aging bout, but they can take off fish to come within range. This re- serves to help them remain station- directly from the water despite quires a heron’s legendary patience, ary in the water. I once watched a their sodden plumage. To do so, but darters face two significant darter dive for more than a minute they habitually raise themselves problems: they don’t have too much in water less than half a metre deep, partly out of the water for a few time to wait because they have surfacing in exactly the same spot seconds with wings spread, ap- to hold their breath while diving, where it dived. parently draining their plumage, and they can’t afford to reveal their An added benefit of their low before struggling into the air. presence by swimming vigorously. buoyancy is that they use much less energy – and oxygen – while right This American Darter or hen you see birds swim- diving. This allows them to remain Anhinga shows how darters ming underwater they underwater for longer without have near-neutral buoyancy appear quite frenetic, building up an oxygen debt. When at the water surface, and use kickingW or flapping continuously, in I compiled the species account for their fanned tail to assist with stark contrast to the more languid the African Darter in Roberts VII, attitude control while waiting action of fish and marine mam- I was amazed to discover that very for fish to move within striking mals. The main reason for this is little was published on darter div- range. that birds rely on the air trapped in ing ecology, so I set about collecting their feathers for insulation, which some data. Compared to cormor­ opposite This bird shows a makes them buoyant, at least near ants of similar size, darters’ dives mosaic of juvenile and adult the water surface. As they dive last roughly twice as long, yet their plumage. It is unknown at deeper, this air layer gets com- recovery periods between them are what age African Darters first pressed, reducing both their buoy- about the same length. This makes start to breed. ancy and their insulation. Darters them extremely efficient divers. >

58 african birdlife july/august 2013 DARTERS 59 After emerging from the water, darters typically sit apparently because they become very secretive during this period. with their wings spread and their backs to the sun. Conventional wisdom is that they This is often termed ‘drying their wings’, but the main retreat to the heart of large swamps, where they can slip unobtrusively reason is to save energy by warming up passively into and out of the water without revealing their temporary handi- Darters replace all Darters typically spend about 80 per sun to warm their skin directly. It cap. However, I recently saw a bird their wing feathers cent of a foraging bout underwater, would be interesting to measure in full moult sitting three metres up at once, becoming more than any other diving bird. how much a darter’s body temper­ in a tree overhanging flightless for several The darters’ unique foraging strat- ature falls during a foraging bout. a busy canal in a coastal marina. I weeks while their egy explains why they are confined The other way in which darters have no idea quite how it got there new feathers grow. to the warmer parts of the world. differ strikingly from cormorants is or how it planned to get down! They are seldom Whereas cormorants breed in the that they moult all their wing feath- Darters have other mysteries still seen during this polar regions and even spend the ers at once. After breeding, they drop to be resolved. For example, no one vulnerable period, winter in Greenland, darters can’t their primaries, secondaries and has yet come up with a convin­cing but the bird on the afford to hunt in cold water because greater coverts, remaining flightless explanation for why the central left is in full moult. they would lose too much body for several weeks while their new tail feathers and elongated scapu- It also puts paid heat. As it is, their fishing sessions feathers grow. They don’t moult their lar feathers of adult birds have to the notion that tend to be quite short, seldom last- tail feathers synchronously, probably transverse corrugations. Sugges- darters spread their ing more than 20 minutes. After because they need their long, stiff tions range from structural bene­ wings to dry them; emerging from the water, darters tails to forage effectively. fits to sexual displays. Fortunately, this bird has no typically sit with their wings spread They presumably select large, per- with the exception of the Oriental wings to dry! and their backs to the sun. This is of- ennial wetlands at which to moult, Darter, Anhinga species remain ten termed ‘drying their wings’, but and may undertake moult migra- common and are relatively easy to the main reason is to save energy by tions in the way that many observe. Maybe next time you see warming up passively. They fluff up and geese do, but this has not been one you’ll look a little closer and their back feathers, just like a Little studied. There are surprisingly few add to our meagre knowledge of Grebe between dives, allowing the observations of darters, these intriguing birds. 

60 african birdlife