Seeds Of The Corsican Pine, A Key Ressource For The Corsican Nuthatch

Pasquale MONEGLIA,

EPHE, CEFE (UMR 5175)

Seeds pine are an abundant and energetic source of food for generalist seedpredators and specialist seed predators.But, in Pinus, cone and seed production have interannual and spatial variations,also seeds and cones characteristics are variables.

The forest’s granivorous develop specific adaptations to their habitat and food. But,these adaptations create a dependency that may be restricting, in case ofdisturbances affecting the productivity of trees (logging, fire,…)

The Corsican nuthatch is sedentary and remains in an area of only a few hectaresthroughout the years, at altitudes above 900 m. Nuthatch develop specificadaptations to their habitat and food, specifically important in winter when laricioseeds are the essential of the diet of nuthactches

Quantify the relationship between the Corsican nuthatch and

Corsican pine seed :

1. the energy needs of the bird

2. energy intake of the seeds

3. availability / accessibility of the resource

Description of Corsican pine seed and cone production :

1. Quantitative aspects of cone crop,

2. Cone and seed caracteristics

3. Spatio-temporal variation of cone crop

4. Dendrometric and fire severity variables influence cone crop

Cones and seeds characteristics

1. Cone harvested before seed dispersal

2. Cones were placed at a temperature of 35°C for twelve hours to trigger the opening and release the seeds

3. Measuresi. Diameter at breast height (DBH)ii. Full and empty seed numberiii. Seed weight

Cone production

1. Monitoring during 3 years : 2004-2005-2006

2. Study area : 8 pinewoods, elevations 150-1400 m.

3. Visual counting

4. 3 diameter classes : 20-49, 50-79, ≥80 cm

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4

2

3

6

1

5

7

8 1 – Tartagine

2 – Aitone-Lindinosa

3 – Vizzavona

4 – Vallée d’Asco

5 – Basse vallée du Golo

6 – Restonica

7 – Basse vallée du Tavignano

8 – Petrapiana – Poggio di Nazza

- light green : pinewood at lowaltitude (altitude below 1000 m)

- dark green : homogeneous standsof altitude (altitude above 1000 m)

To assess the availability of seeds for nuthatches, we quantify four parameters :

Field metabolic rates of Corsican nuthatches: it represents the total daily energy requirement for an animal in the wild.

Equation relating FMR for birds to body weight :FMR (kJ/day) = 10,4×(weight)0,68

Metabolizable energy: it depends on characteristics of both the food and the organism eating it.ME = GE × AE

where:ME = Metabolizable energy (e.g., in kj/g)GE = Gross energy (e.g., in kcal/g) is the total energy content of a foodAE = Assimilation efficiency by animal : AE = 0.75 for the passerineseating seeds

Energy value of Corsican pine seeds, measured with a bomb calorimeter

Cone production/ha

Variation in cone productionSeeds and cones characterists

Variation in number and weight of seed per coneFood needs of the nuthatch

Estimation pinewood area required to maintain a pair of Nuthatch

Cone production is highly variable :

1. The number of cones produced by trees varies according to the year

2. Production varies according to location of trees :

i. production varies from one forest to another for the same years

ii. production varies within forest

iii. production varies between the altitudes

3. Cone production depends strongly on the diameter of pins

Effect of geographical area according to

year, on the cone production

0

20

40

60

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180

NS1 NS2 NS3 NS4

Co

ne

nu

mb

er

pe

r tr

ee

Forest

2004

2005

2006

NS1 Vallée d’AscoNS2 Forêt de Petrapiana-Poggio di NazzaNS3 Forêt d’Aitone-LindinosaNS4 Forêt de Vizzavona

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300 600 900 1200 1500

Co

ne

nu

mb

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Elevation (m)

Année 2006

D=40cm

D=60cm

D=80cm

Effect of altitude and diameter of the tree on

the cone production in 2005 and 2006

0

100

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300 600 900 1200 1500

Co

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Elevation (m)

Année 2005

D=40cm

D=60cm

D=80cm

We have also seen that :

1. Pines with larger diameters are more productive.

2. In the pine forests of altitude(alt.>1000 m.), there are many small producersand few large producers. But large producers produce a large number ofcones constituting the majority of production. They may even be the onlyproducers.

3. Change in proportion of non-producing trees at altitudes above 1000meters : between 13 and 64% depending on the year.

The years of low cone production correspond to the years of low frequencyof producing trees when production is low, it is concentrated on a fewtrees.

And, the proportion of non-producers trees is higher in high altitudeduring the years of low production. However, during the good years, theproportion of non-producers trees was the same regardless of altitude.

YearNumber of

cones measured

Variables Mean min - max

2004 263

Length cone (mm) 53,3 31,7 - 82,1

n seed empty 22 0-57

n seed full 20 1-83

n seed 42 1-97

% seed empty 54 0-98

weight of seeds /cone

299,26 7,7-1542,4

2005348

Length cone (mm) 54,4 30,5-81,6

n seed empty 15 0-49

n seed full 29 0-69

n seed 44 7-79

% seed empty 36 0-100

weight of seeds /cone

418,81 0-1361

46 number of scales 43 26-58

Without being able to identify

the precise reasons, we observed

that could coexist :

1. full seeds

2. empty seeds

3. scales without seeds

developed where only the

wing was present

Full seedsEmpty seeds, with marks of

invertebrates

Sample 1:Asco forestElevation > 1000 mFebruary 2003495 cones from 36 trees

1. The individual weight seed (WGP) varied between the cones and the trees.

2. The individual weight seed (WGP) was influenced by :• DBH,• the number of empty seeds per cone• the total number of seeds per cone

12,0

13,0

14,0

15,0

16,0

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18,0

19,0

20,0

20 40 60 80 100

WG

P

D

NTG=12

NTG=32

NTG=52

NTG=7212,0

13,0

14,0

15,0

16,0

17,0

18,0

19,0

20,0

20 40 60 80 100

WG

P

D

NTG=12

NTG=32

NTG=52

NTG=72

12,0

13,0

14,0

15,0

16,0

17,0

18,0

19,0

20,0

20 40 60 80 100

WG

P

D

NTG=32

NTG=52

NTG=72

12,0

13,0

14,0

15,0

16,0

17,0

18,0

19,0

20,0

20 40 60 80 100

WG

P

D

NTG=32

NTG=52

NTG=72

Effect of diameter (D) on the seed weight (WGP) according to number of empty seeds per cone (NGV) and total number of seeds per cone (NTG)

NGV=0 NGV=11

NGV=22 NGV=32

…but the effect of the diameter depends on the total number of seeds and thenumber of empty seeds :

The weight of seeds per cone (=food quantity per cone) varied between the forestsand the years.

The weight of seeds per cone (=food quantity per cone) was influenced by :• the total number of seeds per cone a positive effect• the number of empty seeds per cone a negative effect• the length of the cone a positive effect• the year 2005 good year• the size of the cone a positive effect

Sample 2 : ForestElevation

(m)

2004 2005

Number

of trees

Number of cones

harvested

Number

of trees

Number of cones

harvested

Vizzavona 1150 9 74 10 83

Petrapiana 1150-1500 9 68 12 89

Asco

1300 6 59 10 97

800 4 34 0 0

440 3 28 10 80

Our knowledge suggest that, at least during the 3 months of winter, the nuthatcheats almost exclusively some seeds. It means that a pair needs at least 50.000 seeds (more than 2 500 cones) peryear, that is to say more than 250 seeds/bird/day.

These quantities are to be compared to the one observed on forest Tits (passerinewith a body weight and a trophic ecology comparable to the nuthatch). Indeed, theseed availability for nuthatches is clearly limited by competition with othergranivores in Corsican pine forest, the main competitor is Coal tit (Parus ater).

Parus ater

Field Metabolic rate = 46.3 Kj/day,but seeds only a third of the diet seeds provide only 15.4 Kj/day

Need food = 80 seeds/day/ind.7 198 seeds/year/ind215 954 seeds/year/10ha

Density =15-21 pairs/10ha

Corsican Nuthatches with densities of only 1 pair/10 ha, collect only

587 seeds/day/10ha

Sitta whiteheadi

Field Metabolic rate = 56.7 Kj/day

Need food = 294 seeds/day/ind.26 446 seeds/year/ind52 892 seeds/year/10ha

Density = 1 pair/10ha .

Coal tits collect more than 2 400 seeds/day/10ha

10 ha 1 pair of nuthatch and 15 pairs of tit needs at least 13 443 cones/year

10 ha (nuthatch

density = 1 pair/10ha),

1300 cones are

required to maintain 1

pair of Nuthatch, and

15 pairs of Coal tit

Area of the stand to feed the Corsican nuthatches and

Coal tits, depending on the production of cones

Area of the stand to feed the Corsican nuthatches and Coal tits,

depending on the production of cones

TerritorySitta

Altitude (m)

Number of cones per ha

Minimale area (ha)

2005 2006 2005 2006X8 1067 34 272 25 377 0,4 0,5

ZA7 1086 22 616 15 116 0,6 0,9V10 1110 29 052 17 131 0,5 0,8T14 1200 31 343 11 640 0,4 1,2ZD9 1240 21 950 6 494 0,6 2,1O23 1285 8 345 1 870 1,6 7,2V16 1310 21 772 4 146 0,6 3,2W15 1310 24 219 4 490 0,6 3,0P21 1315 16 481 3 066 0,8 4,4R22 1330 28 475 4 727 0,5 2,8N24 1337 22 534 3 495 0,6 3,8S20 1400 37 267 3 886 0,4 3,5H25 1465 7 988 487 1,7 27,6

year 2005 : NC = 3,42 + 0,02(D) + 0,002(ALT) - 0,0001(ALT²/100)year 2006 : NC = 3,37 + 0,15(D) + 0,006(ALT) - 0,0005(ALT²/100)

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Altitude of the territory (m)