j Raptor Res. 28(1):19-22
¸ 1994 The Raptor ResearchFoundation, Inc.
RELEASING
MONTAGU'S
(Circuspygargus)BY THE METHOD
HARRIER
OF HACKING
MANEL POMAROL
DireccidGeneraldel Medi Natural, Servezde Proteccio
i Gestiode la bhuna,
c/Cbrsega,329, 5d.08037Barcelona,
Spain
ABSTR^CT.--Thehackingtechniqueis the methodmostfrequentlyusedfor the introductionof birds of
prey.The useof thistechniquein the reintroduction
of Montagu'sharrier (Circuspygargus)is described.
Hacking takesplace in an enclosuremeasuring3-4 m x 2 m x 1 m high. The harriers were between
20 and 30 d of age. After 5-8 d the enclosurewas opened.The young birds becameindependenton
average33.7 d after the first flights(70.5 d of age). Over a 5-yr period87 birds were introducedwith a
success
rate of 82.7%.Only threebirdshavebeenseenreturningto the areain subsequent
years,but it
is still early to be assessing
the success
of the project.
KEY WORDS: Circus pygargus;hacking;releasing.
Reintroducci6n
del Aquiluchocenizopor el matodohacking
RESUMEN.--EIm•todohackingesel matodomascomtlnmente
utilizadoparala reintroducci6n
derapaces.
En el presenteartlculosedescribela utilizaci6nde dichat•cnicaen la reintroducci6n
del aguiluchocenizo.
El hackingse realiza en un cercadode 3-4 m x 2 m x 1 m de alto. Los pollossonsituadosconedades
de 20 a 30 d. Tras 5-8 d el cercadoes abierto.Los pollosalcanzanla independencia
a los 33.7 d desde
el iniciode losprimerosvuelos(correspondiendo
a 70.5 d de edad).Tras un perlodode 5 aftos,87 pollos
han sidoreintroducidos
conun axitodel 82.7%.Aunquehastala fechatan solotresaguiluchoshan sido
vistosvolvera la zonaa losaftossiguientes,
aun estodavlatempranopara evaluarel •xito del proyecto.
[Traducci6n Autor]
Montagu's harrier (Circuspygargus)has suffered barked on a program to reestablishthe species(Poa considerable
declinein the last few years(Cramp marol and Parellada 1989).
and Simmons 1980). In Catalonia (northeastern
For the first few yearsof the projectmostof the
Spain), the populationhas decreased
considerably, methodsdescribedby Berthemyet al. (1983), used
droppingfroman estimated40-55 pairsin the early in the protectionand managementof nests,were
1980s (Muntaner et al. 1983) to 12 pairs in 1985. unsuccessful. Because harvest time most often coAs with mostof the Montagu'sharrier population incideswith incubationor broodingof recently
on the Iberian peninsula(Garzon 1974, De Juana hatchedchicks,the only effectivemeansof nestpro1989), in Cataloniathe species
bredmainlyin grain tectionis to leavean extensivearea (approximately
fieldsand occasionally
in wetland areas.The drain- 0.5 ha) around the nest unharvested(Pomarol and
ing of thesewetlands,and aboveall the destruction Parellada unpubl. data).
of nestingsitesby combineharvesters,are the main
By 1989 only two pairsinitiated breeding.At the
reasons for this serious decline (Muntaner 1981, sametime we begana new strategyto introducethe
Muntaner and CRPR 1985, Blanco and Gonzalez speciesto areasof shortand thick natural vegetation
1992). While the percentageof juveniles fledging (scrub land, marsh areas, etc.), habitats also frebeforeharvesttime (dependingon sitesand years) quentedby Montagu'sharrier in many areasof Euis 40-70% in Italy (Pandolfi and Giacchini 1991), rope (Laszlo 1941, Schipper1978, Cormier 1985).
10-40% in France (Berthemyet al. 1983) and 1050% in Spain (Perez and Fernandez 1971, Fernan- METHODS
Hacking wasthe techniqueselectedfor the introduction
dezet al. 1989), in Cataloniathe overlapof breeding
seasonand cropharvestis sogreatthat at bestonly program. Imprinting acquiredby juvenile birds on the
surroundingsfrom which they start to fly and in which
0-5% fledge.
they will eventuallybe reestablished(Sherrodet al. 1982)
In 1985 the Servei de Protecci6 i Gesti6 de la
is of fundamentalimportanceif introductionis to succeed
Fauna (Wildlife Service of Catalonia State) em-
Hackinghasbeenutilizedto introducemanyspecies
of
19
20
MANEL POMAROL
VOL. 28, No. 1
Table 1. Montagu'sharriersreleased
by hackingin Spain (Jonesand Colling 1984, Leroux 1991, Zijlstra and Hustings 1992), are not presentat this location.
(birds seen10 d after first flights).
The hackingcageconsistedof a seriesof net enclosures
measured3-4 m in length, 2 m in breadth and 1 m in
PERCENT OF BIRDS
height.The enclosures
were placedon a small islandof 9
NUMBER OF
SUCCESSFULLY
ha and surroundedby canalsand small lagoons.In this
YEAR
BIRDS RELEASED
RELEASED
way mammalian predatorswere avoided.
The ideal age for placing the young harriers in the
1988
8
100
enclosureis 21-25 d, sincefrom age 21 d they are able to
1989
5
100
tear their foodalthoughtheyare still unableto fly. Some
1990
14
85.7
birdsover30 d old, however,werealsousedsuccessfully.
1991
31
90.3
Five to eightjuvenile Montagu'sharriers of similar ages
1992
29
65.5
were placed in each enclosure.
For identificationfrom a distance,the young harriers
Total
87
82.7
were
marked
with
colored
bands in addition
to official
metal bands.Subsequently,this methodprovedineffective
sincebandson birds sitting on ground coveredwith vegraptorsand hasbeenadaptedto the characteristics
of each etation were extremelydifficult to see.For this reasonin
species.However, it has not beendescribedfor ground- 1992 we usedwing tags similar to thoseusedby Picozzi
(1971) and Village (1982).
nesters,like most speciesof the genusCircus.
The 87 harrier chicks used for introduction came from
The youngbirds remainedshut in the enclosuresfor a
the followingsources:46 from variouswildlife recovery period of 5-8 d in order to accustomthem to their surcentersin Spain (every spring in the center and south of roundings.The birdswere releasedby pulling back% of
Spain, where harriers are very abundant,the recovery the meshforming the enclosureroof. Initially the enclocentersreceivemany harrier chicksfound by farmersdursureswere openedat night, but we later found that they
ing crop harvesting);24 were taken from nestsin grain couldbe openedduring the day withoutany risk.
fieldsin Catalonia;11 from nestswith largebroodslocated
If the enclosurehad beenopenedat night, the harriers
in scrub land out of Catalonia, and six had been bred in
over 30-32 d old began to make their first flights the
captivity.
followingmorning.Theseflightswere shortand straight,
The site chosen for introduction
was the Parc Natural
and the birds spentmostof the day hiding in the grass.
dels Aigfiamollsde l'Empordfi, a wildlife reservein the At that time the enclosure
couldbe usedfor a new group
provinceof Girona. Extensiveareas of marsh vegetation of chicks.
existhere, and 25 yr ago Montagu's harrier was a resident
From 35 d of ageon, real flightscouldbe observedwith
nesting bird at this location (Wallace and Sague 1969). small ascentsand somegliding. At this stagethey also
That the area is currently under protection,combinedwith beganto play together,chasingeachother throughthe air.
adequate managementof the habitat, makes the introThe daily foodsupplyfor theyoungbirdsalreadyflying
duction of the speciesand its long-term survival there wasleft on top of or besidethe enclosure.Food wasgiven
feasible.The problemsother populationsof Montagu's everyday for five days,or until no food was eatenand all
harrier in similar habitatsin Europe have experiencedor harriers had left.
are experiencing,suchas lossof habitat, disturbance,etc.
Observations
weredonewith a telescope
(20-60 x ) from
a blind locatedat 80 m from the hackingenclosure.Observationslastedabout 6 hr/d, but increasedto all day
No
(12 hr) when harriersstartedto moveaway moreoften.
birds
2O
RESULTS AND DISCUSSION
Between 1988 and 1992, 87 juvenile Montagu's
harrierswere releasedin this way. In addition,during the first 3 yr, six chicksdiedbeforemakingtheir
first flights.Postmortemanalysesdid not revealspecificcauses.We speculated
that transportationof the
birdsoverlongdistancesand possiblybad handling
caused a high degree of stress with fatal consequences.
0
0-4
5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
50-54
55-59
Days (1st flight/lst day independence)
Figure 1. Periodof dependence
(N = 79). A: Birds consideredunsuccessfully
released.B: Birds seenafter first
10 d are considered re-established.
If we assumethe minimal learning period for
juvenilesin the field is 10 d (Cramp and Simmons
1980), and calculate all birds which return to the
enclosure
after(hefirst10d of flightasbeingsuccessfully reestablished,we obtain an introduction
success
rate of 82.7% (Table 1). This minimum pe-
MARCH
1994
HACKING
OF MONTAGU'S
Table 2. Correlation between date of releaseand period
of dependencefor Montagu's harriers in Spain.
NUMBER
DATE
OF RELEASE
OF BIRDS
< 15 July
19-25 July
30 July-4 August
39 d
32.9 d
29.9 d
when
21
Table 3. Correlation betweenage of Montagu's harrier
(at time of openingthe hackingenclosure),period of dependence,and age of independence.
PERIOD OF
DEPENDENCE
18
26
19
rlod seems to be corroborated
HARRIER
AVERAGE
AVERAGE
AGE AT
NUMBER
RELEASE
OF BIRDS
DEPENDENCE
32.4
PERIOD OF
AVERAGE
AGE OF
INDEPENDENCE
d
30
37 d
69.4
35.7 d
10
33.8 d
69.5 d
d
43.2 d
22
29.5 d
73.1
d
we observe the
existenceof two clearly separatedgroups(A and B)
harriers reach 40 d of age they carry small prey
in Fig. 1.
The averageperiod for attaining self-sufficiency (birds, particularly young barn swallows(Hirundo
from first flights to independence(when birds stop rustica))to percheslocatednear the enclosure.
In 1989, two of the birds which had been introcomingback to the enclosurefor feeding)was 33.7
d (N = 63; calculated from birds consideredsuc- ducedthe previousyear returnedto the area. These
cessfullyintroduced),althoughthis variedgreatlyin joined the immature harriers which had beenintroeach case (Fig. 1). Independencecorrespondedto duced that year and ate the food provided.This
70.5 d old on average.This seemsto be extremely suggeststhat the birds acquire a certain degreeof
long when comparedwith observationsof young fixation on the area of release.Despite this initial
fledgangfrom natural nests(10-17 d). One reason success,only one more releasedbird has been refor such differencesis the fact that fledglingswho cordedas returning to the area, and it could not be
received supplementaryfood dispersedat signifi- confirmedthat any pairs had bred in the area.
cantly older age than young from nonexperimental
The low number of individualsreleasedduring
broods(Frumkin in press).
the first few years (Table 1), and the fact that the
Individualswith slightly damagedplumageare speciesdoesnot usually breeduntil reachingthe age
alwaysthe lastto leavethe area, suggesting
that they of 2-3 yr (Cramp and Simmons 1980) suggestwe
have difficulty catchingprey. This emphasizesthe shouldwait a few more years beforeassessing
the
importanceof birds being in perfectconditionwhen resultof the introductionsin termsof reestablishing
released.Damaged birds were recaptured perma- a breedingpopulation.
nently, and were not includedin this analysis.
ACKNOWLEDGMENTS
The periodsof dependenceappear to decrease
I would like to thank all the people who have collabwhen the juveniles are releasedat later calendar
dates (Table 2) (Kruskal-Wallis test H = 9.91, df oratedin carryingoutthehackingovertheyears,especially
S. RomerodeTejada, A. Batlie, D. Saavedraand F. Kirch= 2, P < 0.01). This differencemay be due to the net. Also, I am grateful to V. Ennion for her translation
urge to migrate, as is the casewith the black kite Finally, I thank S.K. Shetrod and W.R. Heinrich for
helpful commentson the manuscript.
(Milvus migrans;Bustamanteand Hiraldo 1990).
Our
results demonstrate
that harriers
released at
a younger age have a longer period of dependence
than thosefreed at an older age (H = 6.77, df = 2,
P < 0.05), while the age at which they become
independentis similar (H = 2.23, df = 2, P > 0.05;
Table 3).
Laszlo (1941) statesthat youngharriers learn to
hunt before becomingindependent.Beske (1982),
however,havingfollowedseveralyoungradio-tagged
northern harriers (Circus cyaneus),did not observe
any hunting activity during the period of dependence.For our part, althoughhunting was not observed,we were able to confirm that oncejuvenile
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Received10 May 1993; accepted30 November 1993