Woodpeckers
Woodpeckers are unmistakable, thanks to their climbing and pecking
habits. Especially impressive however—indeed unique —are their tapping anddrumming communication signals, whichcan be heard in many of the world’s woodsduring the breeding season. With their spe-cialized climbing and pecking methods,woodpeckers are unrivaled as predators oninsects that lie hidden under bark, withinwood, or, like ants and termites, live in nestswith tunnels far below the surface. Wood-peckers also create permanent dwellings forrearing their young and for daily roosting ;excavated holes last for years.
Woodpeckers play an important role inthe earth’s forest eco-systems. They help tocontrol numbers of hark- and wood-boringinsects, thereby contributing to the healthof the tree trunk and its bark covering.Where woodpeckers have pecked, othersmaller birds (tits, nuthatches, treecreepers)can forage successfully for any remaininginsects and spiders, and woodpecker holesare used for nesting or roosting by manyother hole-nesting insectivores. Owls,martens and other mammals also benefitfrom using woodpecker holes. Woodpeckersthus help indirectly to exert pressure on thehuge populations of insects and mice orvoles. They also play an important part inthe cycle of decay and regeneration of mat-ter in so far as they peck at huge amountsof dead wood, making it accessible to otherdecomposing organisms.
True woodpeckers (subfamily Picinae) aresmall- to medium-sized birds of powerfuland stocky build. Their bill is adapted for
hacking and chiseling. Their tongue, cap-able of extreme protrusion (up to rocm, 4in.in the Green woodpecker), is a highly effi-cient catching device which enables the birdto extract insects from deep cracks andcrevices and from the tunnels bored byinsect larvae and made by ants and termites.Woodpecker feet are especially adapted forclimbing, with two toes pointed forward andtwo back. The fourth toe can be bent side-ways so that the crampon-shaped claws canalways be positioned so as best to suit thecurve of trunk or branch. Climbing move-ments and pecking postures are facilitatedby the wedge-shaped supporting tailfeathers, the shafts of which have additionalstrengthening. Such a tail allows the wood-pecker’s body to be cushioned and permitsa good, relaxed posture for pecking or forpauses between bouts of climbing. Specialadaptations for pecking, tapping and drum-ming protect internal organs, particularlythe brain, against impact damage. This isabsolutely necessary considering the number of pecking blows executed daily (in theBlack woodpecker 8,0o0 to 12,000).
True woodpeckers eat mainly arthropods,particularly insects and spiders, but alsotake plant food (fruits, seeds, berries) andnestling birds from holes in trees. The Acornwoodpecker eats acorns, storing these forthe winter in specially excavated holes. Sap-suckers drill holes in horizontal rows (so-called “ringing” behavior) and then lick upthe exuding droplets of sap with the tongue,the tip of which is frayed and brush-like.Great spotted woodpeckers make so-called”anvils” into which they wedge cones in
holes to peck out the fat-rich seeds. Up to5,000 cones may be found under a “pri-mary anvil” of which there will be three orfour in a territory. The ability to deal withfruits and seeds in “anvils” or to store themin holes is a great aid to survival for wood-peckers in areas of winter cold and conse-quent seasonal insect shortages.
Woodpeckers catch their prey with agreat variety of different techniques, thesimplest of which is the gleaning of itemsfrom leaf, branch or trunk. Slightly morecomplicated is probing into bark crevicescombined with the scaling of bark. Both sap-suckers and the Three-toed woodpeckerobtain insects that lie hidden under bark orwithin wood by drilling round holes, insert-ing the tongue and harpooning the item.Other “pecking woodpeckers” and also thelarge species chisel and lever off large piecesof bark and carve out deep holes in theirquest for insects. A Black woodpecker mayconsume up to 90o bark beetle larvae orL000 ants at a single meal. “Ground”woodpeckers mostly peck only funnel-shaped holes in ants’ nests. then extendtheir long “lime-twig” tongue along tunnelsand into chambers to spoon up adult antsand pupae. A Green woodpecker needs toeat about 2,000 ants daily, mostly lawn andmeadow ants. When this is not possible, inextreme winters such as that of 1962-63,a large part of the population will perish.Some species, for example the Yellow-tuftedwoodpecker and Lewis’s woodpecker andrelated species of the genera Melanerpes andCenturus, arc able (like flycatchers andtyrants) to take some insects in flight.
Most woodpeckers are sedentary and mayremain in the same territory for a long time.Only a few species. including the Yellow-bellied sapsucker and the Red-headed wood-pecker in North America, are migratory.Northern races of the Great spotted wood-pecker and the Three-toed woodpeckersundertake far-reaching eruptive move-ments at intervals of several years, whentheir main seed-crop diets fail. The Greatspotted woodpecker penetrates into centraland southern Europe in years of coneshortage ; Three-toed woodpeckers invadeareas of North America and Europe wherethe forests periodically suffer from infes-tations of insect pests.
The great majority of woodpeckers areterritorial, living in individual, pair or familyterritories, in some cases for several years.A ringed Great spotted woodpecker showedfidelity to its 25ha (62 acre) territory for aperiod of 6 years in most other speciesstudied most individuals remained in orclose to their territory for the whole of theirlives. Defending a territory helps to ensurenot only breeding success but also adequatefood supplies and, above all—especiallyimportant for woodpeckers—roosting pos-sibilities in holes affording shelter from theweather. As a rule woodpeckers reactaggressively towards intruders of their ownkind.
Genuine family territories are found in theAcorn woodpecker. Up to r 5 individuals ofdifferent generations live in the territory,providing an effective defense of their acornstores against any competitors.
Woodpecker courtship generally beginswith drumming, display (”excitement”)flights and prominent calls. These signals are used by both sexes to advertise territorylimits and trees with holes, to attract pro-spective partners to suitable nest-sites (nest-showing), to stimulate the partner sexuallyand to intimidate rivals. A new nest-hole isnot excavated every year and an old one cancertainly be used for several years. Blackwoodpeckers may use the same hole for upto 6 years, Green woodpeckers for up toyears or more. However, even these speciesare forced to excavate new holes when theyare evicted by jackdaws or starlings.
Excavation of a hole takes 10-28 days,according to species and method. Both sexesparticipate. About r 0,000 wood chips havebeen found under a Black woodpecker’shole. When the hole is completed the birdschip off small pieces from the inner wall toserve as a cushion in the nest-scrape for eggsand young.
Copulation usually takes place withoutany special ceremony. The female assumesa precopulatory posture—crossways on abranch—and the male simply flies onto herback. Lengthy physical contact is avoided.Mutual courtship feeding has been recordedin only a few species, for example the Olive-backed woodpecker of Asia. The glossywhite eggs are laid in the early morning, oneper day until the clutch is complete. Con-stant guarding of the nest-hole is typicalonce the first egg has been laid. In all speciesof woodpeckers the male spends the nightin the nest-hole during both incubation andnestling periods ; in the Melanerpes wood-peckers, male and female roost theretogether.
During incubation and brooding, birds ofa pair change over at intervals of 30 to150 minutes. The nest-relief ceremonyresembles that of nest-showing : calling,demonstrative tapping, also drumming. The”pecking woodpeckers” collect food in thebill, the “ground woodpeckers” and all largespecies feed their young by regurgitation.Nestlings give almost ceaseless whirring orrattling food-calls.
The nestling period is 18-35 days. Whenthey leave the nest, young woodpeckers canclimb and fly. Soon afterwards they followthe adults through the territory, contactbeing maintained with calls which in Black,Pileated, Green and Gray-headed woodpeck-ers are the same as those given to attracta partner or to guide another bird to a hole.In some species both adults tend the youngafter fledging, in others (eg Great spottedwoodpecker and others of the genusPicoides, and also Green and Gray-headedwoodpeckers) the brood is split, each adultcaring for one to three young. The family breaks up within 1-8 weeks of leaving thenest, adults increasingly using variousforms of threat to drive away their offspring(ruffling of crown feathers, wing-spreading,threat calls) which finally move off, eventu-ally to establish their own territories.
The tiny piculets (subfamily Picumninae)climb about tree branches in the manner ofwoodpeckers or, at times, like titmice andnuthatches. Their flight is undulating. For-aging piculets peck at bark and soft woodto get at ants, termites and wood-boringinsects. Their tail, which does not serve asa support when climbing and does not havethe stiffened quills of the larger woodpeck-ers, shows three conspicuous whitelongitudinal stripes in almost all species.Piculets excavate a nest-hole in tree trunkor branch, or enlarge available holes. Dur-ing courtship they call and drum. The clutchconsists of 2-4 eggs and incubation takes 1-14 days. The young fledge after 21-24days. Disjunct distribution in Asia, Africaand America indicates the piculets to be ofvery ancient origin.
Wrynecks (subfamily Jynginae) live inopen woods, orchards, parks and meadowswith copses. Like woodpeckers they obtaintheir main food (various kinds of ants) withthe help of the tongue. The name wryneckderives from their defense behavior in thenest: when threatened by a predator theyperform snake-like twisting and swayingmotions of the neck and simultaneouslyhiss. Filmed sequences show that suchbehavior is effective in intimidating smallpredators. A prominent feature in spring isthe rather nasal kwee call which risesslightly in pitch and which is given by bothsexes to attract a partner to prospective nest-holes. The 7 or 8 eggs are usually laid on thebare floor of the nest chamber (after throw-ing out any nest that may have already beenstarted). Incubation takes 12-14 days andthe young spend a further 21 days in thenest, the parents feeding them with adult
.and pupal ants (about 8,000 individualsdaily for all the nestlings); post-fledging carelasts 2 weeks.
From July onwards Northern wrynecksbegin their migration south from breedinggrounds in Europe and Asia to winteringareas in Africa and Southeast Asia. Popula-tions of the Northern wryneck are threat-ened and the species has almost completelydisappeared from England in recent years.The Rufous-necked wryneck is found insouthern Africa, including mountainousregions up to 3,0oom ( 0,000ft ). Browncocktail ants Crematogaster make up 8opercent of its diet.