carlson 1998

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Territory Quality and Feather Growth in the White-Backed Woodpecker Dendrocopos leucotosAuthor(s): Allan CarlsonSource: Journal of Avian Biology, Vol. 29, No. 2 (Jun., 1998), pp. 205-207Published by: Wiley on behalf of Nordic Society Oikos

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8/18/2019 Carlson 1998

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Perrins,

C. M. and

McCleery,

R. H. 1985. The effect

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on

the

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uccessof GreatTits

Parus

major.

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I.

1983.

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(ed.).

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331-360.

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M. and

Soler,

J. J. 1996. Effects

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ood

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monedula,

semi-colonial

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377-383.

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K. A. 1989. Predation

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Junco

phaenotus).

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Anim.

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E. and

Nilsson,

J. - A. 1995.Food

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quality,

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reproductive

iming

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the Blue Tit

(Parus

caeruleus).

Ecology

76: 1804-1812.

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.-E.

1990.

Age-specific

ariation n

reproductive

er-

formance

of birds. - In:

Power,

D.

M.

(ed.).

Current

Ornithology,

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Press,

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York,

pp.

251-

283.

JOURNAL

OF AVIAN

BIOLOGY29: 205-207.

Copenhagen

998

Territory

quality

and

feather

growth

in the White-backed

WoodpeckerDendrocopos eucotos

Allan

Carlson,

Department

of

Conservation

Biology,

Swedish

University

of Agricultural

Sciences,

Box

7002,

S-750 07

Uppsala,

Sweden.

E-mail: Allan.

[email protected]

During

the last

decades

the

White-backed

Woodpecker

has

shown a

precipitous

decline

in

many regions

of the

western

Palearctic.

In

this

study

I

ask whether

detoriation

of the forest

breeding

habitat

might

have contributed to this

population

de-

cline

and

contraction of the

species'

range.

By

using

the tech-

nique

of

ptilochronology

it

is

shown

that the bird's

condition

reflects

the

quality

of

the

breeding

territory

as estimated

by

the

density

of

dead and deciduous stems.

Feather

growth

bars were

wider on old museum specimens, suggesting that birds living

55-150

years ago experienced

a

forest

landscape

of

better

quality

than birds do

today.

Once

widespread

in

the

boreal

forests

of

Fennoscan-

dia,

the

White-backed

Woodpecker

Dendrocopos

leu-

cotos has

declined

dramatically

during

the second

half

of

this

century

(Tiainen

1990,

Carlson and

Aulen

1992).

Several

reasons

for

the

decline have

been

suggested,

but

attention

has

mainly

focused on

habitat

loss

(Aulen

1988,

Haland

and

Ugelvik

1990,

Virkkala et al.

1993).

The

White-backed

Woodpecker

has

a

highly specialized diet, consisting mainly of

wood-boring

and

bark-living

insects,

collected

in

dead and

decaying

trees

(Aulen

1988,

1991).

Despite

a

great

interest in

the

species

on the

population

level

(Virkkala

et al.

1993),

little is

known

about

possible

effects

of habitat

deterioration

and

fragmentation

on

the

condition of

individual

birds.

Here,

I

use the

technique

of

ptilochronology

(Grubb

1989)

to

ex-

plore

whether

estimates of

territory

quality

are corre-

lated with

the

nutritional

condition of

the

birds

living

in

these

territories.

Furthermore,

this

data set

is

contrasted

to

feather

growth

measured

on

museum

skins

from the period prior to the introduction of

modern

forestry

methods.

The

technique

of

ptilochronology

uses the width

of

feather

growth

bars

to assess the nutritional status

of

a bird

(Grubb

1989).

Experimental

evidence

indicates

that

growth

bar

width reflects the bird's

nutritional

condition at

the time of moult and feather

growth

(Grubb 1995).

Assumptions

and

utility

of

the

method

are

discussed

in

detail in

Murphy

and

King (1991),

Murphy

(1992)

and Grubb

(1992).

During

field

work

in

spring

(1990-1992),

the

right

fourth

rectrix was

sampled

from

nine birds

(3

females

and 6

males)

cap-

tured

at their

breeding

sites

(nine

different

territories).

This

was

done in

two

of the

three Swedish

subpopu-

lations. The method

adopted

was that

outlined

in

Grubb

(1989).

Because

rectrices were worn

and

dirty

it was

often

possible

to discern

only

five

growth

bars.

These five

growth

bars

were

measured,

and their

means were used in the

analysis.

Adult

White-backed

Woodpeckers

show

a

high

de-

gree of territory fidelity (I. Stenberg and A. Carlson

unpubl.).

Therefore,

I

assume

that

sampled

feathers

had

been

grown

at the

breeding

site

during

the

previ-

ous

moult.

White-backed

Woodpeckers

moult

their

tail in

summer

(Cramp

1988).

The

Museum

of Natural

History (Stockholm)

has a

fairly large

collection of

White-backed

Woodpecker

skins

covering

several

of

the

species'

races.

Eight

skins

were of the

nominate form

leucotos

leucotos and

these were used in

this

study.

Five of

the

skins were

from

Swedish

birds,

and one

skin each from

Norway,

Lithuania and NW

Russia.

These

skins

were collected

between 1832 and 1942, thus being from 55 to 150

years

old.

JOURNAL OF AVIAN

BIOLOGY

29:2

(1998)

205

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8/18/2019 Carlson 1998

3/4

3.0

E 2.5-

2.5

T Ta

2

.0

O

.

1.5

c

0

r-

)

0.5

0.0

I

0

58 117 175 233 292 350

Density

(stems

/ha)

Fig.

1.

Relationship

etween stimates

f

territory uality

and

feather

growth. Regression analysis;

growth

=

1.48

+

3.8

x

10-3

deciduous

stems/ha (broken ine);

F,7=

9.4,

r2

=0.57,

p

<

0.02; growth

=

1.48

+

7.56

x

10-3

dead

stems/ha (solid

line);

F1,7

=

9.01,

r2

=

0.56,

p

<

0.05.

Two

components

of

territory

quality,

density

of dead

stems and

density

of deciduous trees were

quantified

as

follows.

At

intervals of

100

m,

areas

of

20

x

50 m

were

censused for

growing

and dead stems

(standing

or

fallen)

with a

breast

height

diameter

(bhd)

> 10 cm.

This

was done at

10

points along

a north-south transect

and at 10

points

in

an

east-west

transect

centered

on

the

previous year's cavity

tree.

Thus,

for

each

territory

20

plots

of 0.1 ha were censused.

Due

to

the limited

sample

size it was not

possible

to

control for the effect of sex.

Feather

growth

bar width was measured on

eight

55-150

years

old White-backed

Woodpecker

and were

on

average

broader

(3.71

+ 0.41

mm)

than on birds

living today

(2.20

+

0.36

mm;

Mann-Whitney

U-test,

U

=

9,

p

<

0.05).

A linear

regression analysis

revealed a

positive

rela-

tionship

between the densities

of

dead and live decidu-

ous stems found

in

the White-backed

Woodpecker

territories

and

feather

growth (density

of dead trees

r2

=

0.56,

density

of

deciduous trees

r2

=

0.58)

(Fig. 1).

A multiple step-wise regression analysis indicated that

68%

of the variation in feather

growth

bar width was

explained

by

these two

variables

(F2,6

=

6.2,

r2

=

0.68,

p

=

0.03).

The

important

result

of

this

study

is

that the bird's

nutritional

condition,

measured as

feather

growth

bar

width,

was associated

with two

estimates

of

territory

quality, namely

the

density

of

dead

stems and

the

density

of

deciduous

trees. This

result corroborates the

findings

of another

study

in which the

density

of hunt-

ing perches

and habitat

type

influenced feather

growth

in

the

Loggerhead

Shrike Lanius ludovicianus

Josef

and

Grubb 1992, Grubb and Josef 1994). Due to the White-

backed

Woodpecker's specialization

on larvae of wood-

boring

insects

(Aul6n

1988),

it was not

surprising

that

dead stems

affected

the birds'

nutritional condition.

That also

the

density

of

deciduous

trees

can influence

the

birds' nutritional

condition could

likewise

be ex-

pected.

Deciduous

trees,

especially

old

stems,

can

carry

many

dead and

decaying

branches

(Carlson

unpubl.),

and these are

frequently

used

by foraging

White-backed

Woodpeckers (Aul6n 1988).

An

alternative

explanation

for

the

results is that

high

quality

birds are found

in

high quality

territories

while

low

quality

ones reside

in

territories of

poor quality.

Thus,

the observed

relationship

between feather

growth

and

territory quality

may simply depend

on

the

quality

of the individual bird

rather than habitat.

However,

I

have not

assessed the

quality

of individual birds.

On the

museum

skins,

wing lengths

were measured

as an index

of

bird

size.

There was no

indication that

long-winged

birds

grew

feathers with

wider

bars

(r

=

-0.43,

p

=

0.28).

Interestingly,

the

historical

comparison suggests

that

birds were

living

under better

nutritional conditions

in

the

past.

It is a well-known

fact

that

in

today's

man-

aged

forest

landscape

the

density

of

both deciduous

trees

and dead stems

has

been

severely

reduced.

In

the

late

19th

century,

the volume

of

dead

stems

in

Swedish

forests was

approximately

20% while the

corresponding

figure

today

is as

low

as 1%

(Linder

and

Ostlund

1990).

The

proportion

of deciduous trees

was

probably

around 30%

by

the end of the last

century

(Olsson

1992).

Within the

early

20th

century

distribution

range

of the

species, today

the

proportion

of deciduous trees

in the landscape is 2-4% (Olsson 1992).

To

conclude,

suitable habitat for the White-backed

Woodpecker, old-growth

deciduous

forest

(Carlson

and

Stenberg

1995),

is an

extremely

scarce resource

in

to-

day's rationally managed

forest

landscape.

The results

presented

here

support

the

view

that the observed de-

cline of White-backed

Woodpeckers

in

Sweden

is

caused

by

deterioration

of

the forest

landscape.

Acknowledgements

I thank Dr. T. Part for commentsand

discussion

of

the

manuscript.

The

help

of

Dr.

G.

Frisk at the

Museumof Natural

History

was invaluable.

This

project

was

supported

by grants

from WWF-Sweden

and

the

Swedish

ResearchCouncil orAgriculture ndForestry.Thepaperwas

written

while I

was financed

by

the latter

organization.

References

Aul6n,

G. 1988.

Ecology

and

distribution

of White-backed

Woodpecker

Dendrocopos

eucotos

n

Sweden.

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Swedish

University

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Wildlife

Ecology,Report

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1991.

Increasing

nsect abundance

by killing

deciduous

trees:a method

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improving

he food situation

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gered

woodpeckers.

Holarct.Ecol. 14: 68-80.

Carlson,

A. and

Aul6n,

G. 1992. Territorial

ynamics

n

an

isolatedWhite-backedWoodpeckerDendrocoposeucotos

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and

Stenberg,

I.

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hackspett

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Sciences,

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of

Wildlife

Ecology, Report

No. 27.

(In Swedish.)

Cramp,

S.

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Birds

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Oxford

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of some

empiri-

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-

1995.

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review

and

prospective.

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Power,

D.

M.

(ed.).

Current

Ornithology,

Vol.

12.

Plenum

Press,

New

York,

pp.

89-114.

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and

Yosef,

R. 1994.

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utritionalcondi-

tion

in

Loggerhead

Shrikes

(Lanius

ludovicianus):

Evi-

dence from

ptilochronology.

Auk

111:

756-759.

Hiland,

A. and

Ugelvik,

M.

1990. The status

and

manage-

ment

of

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(Dendrocopos

leuco-

tos)

in

Norway.

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In:

Carlson,

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Aul6n,

G.

(eds).

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partment

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Grubb,

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J. 1990. Distribution

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Copenhagen

1998

Genetic

confirmationof

non-identical

embryonic

twins in the

House

Sparrow

Passer

domesticus

Simon C.

Griffith

and

Reuven

Stewart,

Department of Zoology, University

of

Leicester,

Leicester,

UK

LE1

7RH.

E-mail:

sg4Oje.ac.uk

During

routine

ornithological

monitoring

of a free-

living

population

of

House

Sparrows

Passer

domesti-

cus on

Lundy

Island,

England,

an

unhatched

egg

from

an otherwise successful

clutch of four

was

found

to

contain two

intact

embryos.

The

embryos

were

comparable

in

size,

and were at an

equally

ad-

vanced

stage

of

development

(estimated

as

being

within

two

days

of

hatching, assuming

an incubation

period

of 11

days

(Seel

1968)).

PCR

amplification

of

extracted

DNA

(Primmer

et

al.

1995)

at three

microsatellite

loci

(Neumann

and

Wetton

1996)

identified the twin

embryos

as full sib-

lings,

but

resulting

from

separate

maternal

gametes

(Fig.

1,

Table

1).

In

addition,

SSCP

analysis

of

a

sex-specific

PCR

product

(Griffiths 1995)

distin-

guished

the

embryos

as of different

sexes.

Twinning

in

birds is rare

(Berger

1953,

Batt et al.

1975)

and is

typically

attributed to

cleavage

during

the

early stages

of

development resulting

in

identical,

monozygotic

twins

(Sturkie

1946).

Clearly,

the

pres-

ence of

dizygotic

House

Sparrow

twins of

different

sexes cannot

be due to

cleavage.

Two

scenarios

Table 1.

Allotypes

of

parents

and

twin

offspring

at three

microsatelliteoci. Alleles

have been

assignedarbitrary

etters

for

illustrative

urposes.

Locus

1

Locus

2

Locus 3

(Pdop3) (Pdo

L4)

(Pdo

gS5)

Male

ab

ef

ij

Female

cd

gh kj

Twin2 ad eh jj

JOURNAL OF

AVIAN

BIOLOGY 29:2

(1998)

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