The use of ex­treme cau­tion has cre­ated an­other bar­rier to land ac­cess: the risk of dis­tur­bance due to hunt­ing. The pres­ence of Aus­tralasian bit­tern is in­creas­ingly used as a trig­ger for wet­land clo­sures but dur­ing the 2017 sea­son there was a move to limit hunter ac­cess due to the en­dan­gered or­ange bel­lied par­rot.

Re­spected wildlife bi­ol­o­gist Dr Gra­ham Hall and Ali­son Cash from the Univer­sity of New Eng­land an­swer the im­por­tant ques­tion: what is dis­tur­bance and what does it mean for wa­ter­fowl man­age­ment?

The open­ing of the Vic­to­rian duck hunt­ing sea­son has come and gone with the usual sen­sa­tion­al­ism in­tended to pro­voke neg­a­tive pub­lic in­ter­est at the ex­pense of ac­cu­racy from var­i­ous an­i­mal rights groups. But one thing that was new this year was the pre-sea­son clo­sure of four hunt­ing lo­ca­tions be­cause of ‘dis­tur­bance’. This got us think­ing — what is dis­tur­bance and how is it mea­sured; what is being dis­turbed; who or what is mak­ing the dis­tur­bance; what are the ef­fects of dis­tur­bance; and how do we man­age for dis­tur­bance?

To start, we have con­cen­trated on dis­tur­bance to wa­ter­fowl, specif­i­cally ducks, feed­ing and roost­ing dur­ing non­breed­ing pe­ri­ods; this is the usual sce­nario when the duck harvest oc­curs in south­east­ern Aus­tralia. We have as­sumed that the dis­tur­bance that forced the clo­sure of the four lo­ca­tions was caused by hu­man ac­tiv­ity — specif­i­cally hunt­ing. To as­sume oth­er­wise would im­ply the mere act of walk­ing on to a State Game Re­serve could be classed as dis­tur­bance and there­fore could be used as an ex­cuse to close all Game Re­serves — an ig­no­rant as­sump­tion. In look­ing at dis­tur­bance through hu­man ac­tiv­i­ties there is also an­other fac­tor to con­sider, which is the re­sponses shown by birds of the same, and dif­fer­ent, species to hu­man ac­tiv­i­ties at dif­fer­ent times and in dif­fer­ent lo­ca­tions. For ex­am­ple, the al­leged dis­tur­bances from hunt­ing black ducks over de­coys dur­ing the day may il­licit dif­fer­ent re­sponses from spot­light­ing Pinkeared ducks at night from a boat. Study­ing dis­tur­bance The host of vari­ables un­der­ly­ing the in­ter­ac­tions be­tween ducks and peo­ple makes it dif­fi­cult to ac­cu­rately as­sess what is the cause and the im­pli­ca­tions of a par­tic­u­lar recre­ational dis­tur­bance. This is par­tic­u­larly true for ob­ser­va­tional stud­ies. Whilst these stud­ies can es­tab­lish an ap­par­ent ef­fect be­tween hu­man dis­tur­bance and a re­sponse from the birds, it is not pos­si­ble to es­tab­lish whether hu­man dis­tur­bance adds to or re­places natural dis­tur­bance such as would oc­cur from birds of prey. Fur­ther­more, the mag­ni­tude of the dis­tur­bance may be from col­lec­tive ef­fects of more than one ac­tiv­ity. For ex­am­ple, in the UK wa­ter­fowl num­bers and us­age of a wet­land were af­fected more by hunt­ing, plus the pres­ence of peo­ple en­gaged in other wet­land-based ac­tiv­i­ties, rather than just hunt­ing alone. In a Vic­to­rian con­text, hunt­ing plus pro­test­ers on a wet­land may have a greater ef­fect on dis­turb­ing ducks than ei­ther hunt­ing or pro­test­ers alone!

Most over­seas stud­ies on dis­tur­bance have re­lied on ob­ser­va­tional or semi ex­per­i­men­tal ways of record­ing dis­tur­bance and so can­not eas­ily be used to de­ter­mine the ex­tent of any im­pact of hu­man dis­tur­bance on the birds. Con­versely, it is just as dif­fi­cult to demon­strate there is no im­pact on ducks from a par­tic­u­lar ac­tiv­ity, so a worth­while rec­om­men­da­tion is that any fu­ture research should con­cen­trate on more ex­per­i­men­tal field ma­nip­u­la­tions and adap­tive man­age­ment as a way of con­trol­ling for the many vari­ables.

How­ever, known general features of duck ecol­ogy and pop­u­la­tion dy­nam­ics do help by pro­vid­ing a frame­work in which to judge dis­tur­bance ef­fects. For ex­am­ple, many stud­ies in the USA and the UK have shown that birds con­cen­trate where feed­ing is best, and birds forced to move away from these places by dis­tur­bance have an in­creased risk of changes to their en­ergy bal­ance. The sever­ity of any changes to a bird’s en­ergy bal­ance will vary in com­plex ways such as whether there are al­ter­na­tive feed­ing sites nearby, whether the birds are breed­ing and nest­ing at the time of the dis­tur­bance, or whether the birds mov­ing are adult or ju­ve­niles.

Dis­tur­bance in it­self does not al­ways im­ply a se­ri­ous problem to the birds in the short term. This is be­cause ducks can com­pen­sate for dis­rup­tions to their natural be­hav­iour in var­i­ous ways. For ex­am­ple, some species and in­di­vid­u­als do not al­ways feed at the same time,

sothese birds can com­pen­sate for time lost through dis­tur­bance by feed­ing at other times or feed­ing for longer when the dis­tur­bance has stopped. Hence even ap­par­ently high rates of dis­tur­bance to feed­ing does not au­to­mat­i­cally lead to ma­jor re­duc­tions in food in­take or us­age of feed­ing ar­eas. Com­par­a­tive un­der­stand­ing of the sig­nif­i­cance of dis­tur­bance to ducks de­pends on un­der­stand­ing whether the birds have a buffer­ing ca­pac­ity be­fore fac­ing a re­duced en­ergy bal­ance, and so po­ten­tially re­duced survival.

An­other les­son to be learnt from us­ing wa­ter­fowl ecol­ogy and pop­u­la­tion dy­nam­ics to un­der­pin an un­der­stand­ing of dis­tur­bance is the need to dis­tin­guish be­tween ef­fect and im­pact, and whether it is in­di­vid­u­als or pop­u­la­tions that are af­fected. Many stud­ies re­port lo­cal ef­fects on some in­di­vid­u­als, but it is much harder to de­tect whether such changes have such an im­pact on wa­ter­fowl pop­u­la­tions that the en­tire re­gional pop­u­la­tion de­clines. Also, Aus­tralian ducks are very no­madic so any ef­fect of dis­tur­bance at a lo­cal level may have its im­pact many thou­sands of kilo­me­tres away.

Who is most dis­turbed, by whom, where and when?

Hu­man dis­tur­bance adds to a back­ground of dis­tur­bance from natural causes, such as birds of prey forc­ing birds to aban­don feed­ing grounds. The ef­fects of ad­di­tional dis­tur­bance may be se­ri­ous at those times when birds are hav­ing dif­fi­cul­ties in find­ing suf­fi­cient food, such as dur­ing droughts and low water lev­els. These are times when birds are close to the limit of their en­ergy bal­ance, and en­ergy de­mands rise whilst search­ing for food. Even with­out ad­di­tional dis­tur­bance some duck species reg­u­larly have in­creased mor­tal­ity dur­ing these stress­ful times.

There are general re­la­tion­ships be­tween who and what causes dis­tur­bance to wa­ter­fowl. Sev­eral stud­ies have shown that the most wide­spread and long last­ing dis­tur­bance of­ten comes from air­craft, and that the slower the air­craft, the worse the dis­tur­bance. In an Aus­tralian sense this find­ing is very ironic given that gov­ern­ment agen­cies rely so heav­ily on data from the East­ern Aus­tralian aerial wa­ter­fowl counts for their knowl­edge of wa­ter­fowl abun­dance and dis­tri­bu­tion. Over­seas stud­ies im­ply that fly­ing over a wet­land at 150 knots at 30 m as a part of the East­ern Aus­tralian aerial wa­ter­fowl counts is caus­ing greater dis­tur­bance than hunt­ing, and cer­tainly caus­ing greater dis­tur­bance than fly­ing at 60 m at a forward speed of 4m/sec­ond in a drone as estab­lished by this univer­sity in 2015.

On some wet­lands peo­ple and an­i­mals (es­pe­cially dogs) can cre­ate worse dis­tur­bance than peo­ple who stay in one place for some time. For hunters and pro­test­ers alike this is a problem. Hunters usu­ally hunt wa­ter­fowl over de­coys and stay in the one place and al­low the birds to come within shoot­ing range. But once the bird has been shot it is of­ten re­cov­ered by a re­triev­ing dog or the hunter break­ing cover to re­trieve the bird. In a sim­i­lar fash­ion the ac­tiv­i­ties of the pro­test­ers in mov­ing around the wet­lands close to roost­ing ducks and wav­ing flags and us­ing whis­tles may place more stress on the ducks more than if they did not en­gage in these ac­tiv­i­ties. Hunters and pro­test­ers ap­proach­ing from the water seem to gen­er­ally dis­turb ducks more than ap­proach­ing from the land.

A wide­spread as­sess­ment of hu­man dis­tur­bance to ducks sug­gest that con­flict is not a ma­jor is­sue be­cause the birds can fly else­where to avoid the dis­tur­bance. How­ever, the real sit­u­a­tion is of­ten more com­plex than the­ory. The size of the area being dis­turbed may af­fect the level of dis­tur­bance — on small wet­lands there may be few al­ter­na­tive lo­ca­tions avail­able for the birds mov­ing away and it only takes a few dis­tur­bances in dif­fer­ent places to make the whole area un­suit­able for some species.

The type and scale of re­sponse by dif­fer­ent species to dis­tur­bance is also vari­able. Even in­di­vid­ual birds of the same species can re­act in dif­fer­ent ways at dif­fer­ent times of their an­nual cy­cle and on dif­fer­ent wet­lands. We have all seen how Moun­tain ducks are very alert when peo­ple walk to­wards them, and Wood ducks stand­ing on the bank of a farm dam will usu­ally alight on the water when peo­ple ad­vance in their direction. Pink-eared ducks and Grey teal usu­ally take to the wing when they feel dis­turbed.

Wa­ter­fowl man­age­ment in re­gards to hu­man dis­tur­bance

Al­though there are many in­stances where wa­ter­fowl and peo­ple ap­pear to co ex­ist with few or no dam­ag­ing im­pacts, there are also many ex­am­ples where ef­fects and im­pacts of vary­ing sever­ity have been de­scribed. Cu­ri­ously, our searches have found none of these ex­am­ples in the sci­en­tific lit­er­a­ture from Aus­tralia, but per­haps that says more about the lack of research on wa­ter­fowl in this coun­try than it does about dis­tur­bance!

Clearly peo­ple’s recre­ational and other ac­tiv­i­ties around wet­lands can and do lead to dis­tur­bance with of­ten un­in­tended con­se­quences. Our guid­ing prin­ci­ple for man­age­ment of hu­man ac­tiv­i­ties in ar­eas that sup­port im­por­tant wa­ter­fowl pop­u­la­tions would be to limit the over­lap be­tween peo­ple and wa­ter­fowl in time and space. Such a prin­ci­ple oc­curs now in Aus­tralia through wildlife leg­is­la­tion and pol­icy, recog­nis­ing the need for con­ser­va­tion mea­sures for birds whilst also ac­knowl­edg­ing le­git­i­mate hu­man uses, such as hunt­ing. Agree­ments of this na­ture recog­nise the need for in­for­ma­tion on the pat­tern and dis­tri­bu­tion of po­ten­tially dis­turb­ing ac­tiv­i­ties on wa­ter­fowl pop­u­la­tions, rather than in­di­vid­ual species, wet­lands or hu­man ac­tiv­i­ties.

The need for pop­u­la­tion-scale ex­per­i­men­tal stud­ies is why the clo­sure of the Vic­to­rian wet­lands in 2017 for al­leged dis­tur­bance was trou­bling. What cred­i­ble ev­i­dence was there that hunt­ing would dis­turb the birds, what mea­sure­ments were taken to doc­u­ment any dis­tur­bance, and what lessons were learnt so as to avoid sim­i­lar is­sues in the fu­ture? On all ques­tions the avail­able ev­i­dence is that there was no ev­i­dence and the Game Man­age­ment Au­thor­ity has learnt noth­ing by rec­om­mend­ing such clo­sures.

Fu­ture Di­rec­tions

Con­tin­u­ing to in­te­grate the dif­fer­ent hu­man uses of a wet­land with the con­ser­va­tion of no­madic wa­ter­fowl pop­u­la­tions is one of the keys to achiev­ing suc­cess­ful adap­tive man­age­ment. Such in­te­gra­tion can be achieved in a va­ri­ety of in­clu­sive ways. For ex­am­ple, through ed­u­ca­tion and the pro­vi­sion of in­for­ma­tion, and through vol­un­tary and statu­tory agree­ments and des­ig­nated hunt­ing zones. There is lit­tle doubt that non­hunt­ing refuges are im­por­tant, and this is recog­nised by hunters and man­agers alike. How­ever, im­ple­ment­ing the best ap­proach to min­imis­ing dis­tur­bance to wa­ter­fowl in each wet­land de­pends on a bet­ter un­der­stand­ing of the be­hav­iour of both birds and peo­ple. In this con­text, clos­ing a wet­land be­cause of dis­tur­bance achieves noth­ing un­less we learn from the ex­pe­ri­ence and adapt our man­age­ment in the fu­ture, based on what was learnt from the clo­sure.

There are many key top­ics re­quir­ing fur­ther research on the ef­fects of dis­tur­bance on Aus­tralian wa­ter­fowl. Our wish list of research top­ics in­clude:

• Re­view­ing the sci­en­tific lit­er­a­ture and research on the re­la­tion­ship be­tween eco­log­i­cal and recre­ational is­sues, par­tic­u­larly in an Aus­tralian con­text;

• Es­tab­lish stan­dard­ised sci­en­tific meth­ods for as­sess­ing recre­ational dis­tur­bance and im­pact on wa­ter­fowl;

• Ex­per­i­men­tal pro­jects on habi­tats and species to es­tab­lish when dis­tur­bance may have se­ri­ous im­pacts on pop­u­la­tions, not in­di­vid­ual birds; and,

• So­cial stud­ies to ex­plore peo­ple’s at­ti­tudes to recre­ational dis­tur­bance, Ac­cord­ingly, we sug­gest that more ef­fort is re­quired to achieve an un­der­stand­ing of fluc­tu­a­tions in wa­ter­fowl pop­u­la­tions at in­di­vid­ual wet­lands and within dif­fer­ent re­gions. We also en­cour­age an in­creased use of on-go­ing sci­en­tific stud­ies on pop­u­la­tions, in con­trast to the cur­rent ob­ser­va­tional stud­ies or hands-off ap­proach to wa­ter­fowl. Only by ex­am­in­ing the full ge­o­graph­i­cal range of a species and the fac­tors in­flu­enc­ing its dis­tri­bu­tion and survival will we be able to be­gin to an­swer some of the ques­tions around dis­tur­bance.

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