Natal and breeding dispersal in the Baltic Greylag Goose Anser anser

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jL. Dispersai from the centre of the breeding range of the Baltic. Greylag Goose Anser anser was studied using observa tions of individuals with neck collars.
D ispersal of Greylag Geese 21

Natal and breeding dispersal in the Baltic Greylag Goose Anser anser L. Nilsson & H. Persson

D e p a rtm e n t of A n im a l Ecology, U niv e rs ity of Lund, Ecology B u ild in g , S -223 62 Lund, Sweden. E m ail: le if.n ils s o n 0 z o o e k o l.lu .s e .

D isp e rsa i fro m the ce n tre o f the b reeding range o f the B a ltic

jL

Greylag Goose A n s e r a n s e r was s tu d ie d using o b se rva ­ tio ns o f in d iv id u a ls w ith neck c o lla rs . The m edian n a ta l d is p e rs a l d istance was 0 km in fe m a le s and 25 k m in mates, respectively. A ll o f the fe m a le s re c ru ite d to w ith ­ in 7 km o f w here th e y had been reared, 87% to the n a ta l la ke and 11% to n e ig h b o u rin g w a te r bodies. Of the m ates, o nly 11% re c ru ite d to the n a ta l lake, w h ile one in d iv id u a l was fo u n d m ore than 1,000 km fro m its place o f b irth . Even though the m a le s d isp e rse d to a g re a te r d istance w ith in the p o p ­ u la tio n 's b re e d in g range, th e ir d is trib u tio n was s till h ig h ly s ke w e d tow ards th e ir p o in t o f o rig in . Two th ird s o f a ll m ates re c ru ite d w ith in 30 km o f the site w here they had been reared. Once re c ru ite d , both sexes e xh ib ite d an e x tre m e ly s tro n g p h ilo p a try to th e ir b re e d in g area. Only 1.5% o f the m ales and 0.5% o f the fe m a le s changed b re e d in g site betw een successive years. A lt bre e d in g d is p e rs a l o c c u rre d w ith in the lo c a l p o p u la tio n , and in no case exceeded 6 km. K e y W o r d s : B re e d ing d is p e rs a l, n a ta l d is p e rs a l, Greylag Goose, Sweden

“ The q u e stio n of th e r e tu rn of birds to t h e i r

homes

is one

m odern

b e h a v io u r a l

t e r m i n o lo g y .

of p e re n n ia l

M o v e m e n t fr o m th e site of b irth to th a t

interest. How fa ith fu lly do a d u lt birds,

of firs t re p ro d u c tio n o r p o te n tia l re p r o ­

m a le s and fe m a le s , re tu rn to t h e i r t e r ­

d u c tio n is te r m e d n a ta l d is p e rs a l, w h ile

rito rie s ? H ow fa r fr o m t h e i r b irth place

s u b s e q u e n t m o v e m e n t betw een site s is

do young b irds se ttle ? Over ho w m u c h

te r m e d breeding d is p e rs a l (Greenwood

g ro u n d does one fa m ily s c a tte r? " (Nice

1980).

1937). These q u e s tio n s r e m a in highly

D is p e rs a l p a tte rn is of f u n d a m e n ta l

relevant today, th o u g h n o w p hrased in

im p o rta n c e to s e v e ra l a s p e c ts of pop u -

© W ild fo w l & W e tla n d s T r u s t

W ild fo w l [2001 ) 52: 2 1 -3 0

22 D ispersal of Greylag Geese

lation biology, being an e s se n tia l c o m ­ ponent

of

g e n e tic

d y n a m ic s ,

stru ctu re

and

in fe rio r

q u a lity ,

re s u ltin g

in

an

and

e xcep tio na lly high ra te of c o lla r loss

flo w ,

a m o n g m a les. For th a t reason, a ll in d i­

e v o lu tio n a r y

v id u a ls m a r k e d w ith su ch c o lla rs w e re

m e ta -p o p u la tio n

s o u rc e -s in k

an

ge n e

change. However, la rg e -s c a le s tud ie s

excluded fr o m th e analysis.

a d d re s sin g th e se issues are rare (for a

D urin g th e years 1985-1999, re g u la r

1997).

c h e c k s fo r th e o c c u rre n c e of neck c o l ­

Detailed field s tu d ie s are a p p ro p ria te

lared geese w e re u n d e rta k e n fr o m the

fo r in vestigatin g s m a l l- s c a le d ispersal,

tim e of t h e i r a rr iv a l in s p rin g u n til th e ir

sum m ary,

see

C la r k e

e t at.

but they are u s u a lly unab le to fo llo w

d e p a rtu re

in divid u als th a t leave th e stu dy area.

stu d y area w a s visited s e v eral ti m e s a

S m a l l- s c a l e

w e e k in o rd e r to e s ta b lis h th e re tu rn of

s tu d ie s

are v a lu a b le

in

in a u tu m n .

In s p rin g , th e

e va luatin g th e p ro x im a te ca uses of d is ­

m a r k e d birds and t h e i r breeding p e r ­

persal, but d is p e rs a l o u tsid e such local

fo r m a n c e . F ro m th e end of May u n til

areas can only be s tu die d w ith a m a r k ­

th e last young fledged, th e breeding

ing

area w a s visited a lm o s t daily to e s ta b ­

schem e

o p e ra tin g

over a m u c h

la r g e r scale. Neck

lish

c o l la r i n g

of

both

th e

fate

of each

neck

c o lla re d

b re e d in g

gosling . G o slin g s w e re neck c o lla re d

a d u lt and g o s lin g Greylag Geese A n s e r

fr o m th e age of a b o u t six w e e k s u n til

anser, has been u n d e rta k e n a n n u a lly in

th e y w e re

flyin g

and

i m p r a c t ic a l to

s o u th w e s te r n Scania, in s o u th e r n m o s t

catch. In s u m m e r and a u tu m n , fi e l d ­

Sweden since 1985 (N ils so n & P ersson

w o rk

1994,

B e s id e s

n e ig h b o u rin g s ta g in g areas, espe cially

d etailed s tu d ie s in th e b reeding area,

th e Foteviken area on th e coast w h e re a

N ils s o n

e t at.

1997).

was

e x te n d e d

to

co v e r

been fo llo w e d

large p ro p o r tio n of th e Greylag Geese

o u tsid e th e stu d y area by a n e tw o rk of

fr o m th e s tu d y area g a th e r at th is tim e

v o lu n te e rs . Thus, w e are now able to

of ye a r (ef. N ils s o n & Persson 1992).

th e s e

birds have a lso

analyse n a tal and b reeding d is p e rs a l th roughout

th e

B a lt ic

p o p u la t io n s

bre e d in g range.

K n o w le d g e

of

b ird s

r e c r u it e d

o th e r p a rts of th e species'

to

breeding

range is based m a in ly on re p o rts fr o m a n e tw o rk of m o re th a n 1,000 vo lu nte e rs. Observers are located across m u c h of

Methods

the p o te n tia l d is trib u tio n A to t a l of 1,014 g os lin gs , 552 m a le s and 462 fe m a le s w e re ne ck c o lla re d in Lakes

K lo s t e r v ik e n ,

F jä llfo ta s jö n th e y e a rs

and

B ö r r i n g e s jö n ,

Y ddin gesjön

1985-1994

(P ersson

d u rin g 1994,

2000; F igure D.The fir s t g e n e ra tio n of neck c o lla rs used in th e pro ject w a s of

m arked

geese,

a l th o u g h

area of the th e r e

is a

m a rk e d bias to w a rd s th e N e th e rla n d s . F ie ld w o rk outsid e th e stu d y area was lim ite d to ir r e g u l a r visits, m a in ly in late s u m m e r and a u tu m n , to lakes situated w ith in 30 k m of o u r stu d y area. A bird defined as having eggs or

D isp e rsal of Greylag Geese 23

rtJdingesjönt

Fjallfotasjon ÎBjork>sà Krasjon

K losterviken'

10 km

Total

Lake

P ercentage in n a ta l lake

1. Yddingesjön

10

6

12

28

36

2. B ö rrin g e s jö n

4

6

7

17

24

3. K lo ste rvike n

1

11

15

27

4

4. F jä llfo ta s jö n

0

6

4

10

0

Total

15

29

38

82

18

re a rin g period and the

p ro p o rtio n of

in Lake Yddingesjön, th e lake o ffe rin g

m a le s s u b s e q u e n tly re c r u itin g to t h e i r

th e

n a ta l lake [Table 1, S p e a rm a n r=0.73,

o th e r hand th e r e w a s no su c h te n d e n c y

best fe ed in g th e

c o n d itio n s .

m in o rity

of

On th e

P