“The Effect of Agricultural Land Use Patterns on the Breeding of Spotted Eagles in Estonia”

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The effect of agricultural land use patterns on the breeding of spotted eagles (Aquila clanga, Aquila pomarina) in Estonia Ăœlo Väli, Gunnar Sein, Urmas Abel and Joosep Tuvi


Spotted Eagles

• Nest in forests


Spotted Eagles • Hunt in open landscapes, mostly on grasslands


Spotted Eagles • Feed mostly on small rodents, but also on frogs and birds


The Greater Spotted Eagle Aquila clanga • 5-10 breeding territories in Estonia (incl. mixed pairs hybridising with A. pomarina)

• Decline during the last 10 years (at least!)


The Lesser Spotted Eagle Aquila pomarina • 600-700 breeding territories in Estonia • Stable population, threatened by the intensification of agriculture


Habitats differ by species Greater A. clanga – Natural landscape – Flood-plain meadows near rivers – Wet decidious old-growth forests

Lesser A. pomarina – Closer to human settlements – Various grasslands – Spruce-dominated forests

But are overlapping in some extent

CORINE Land Cover data analysed in Lõhmus & Väli 2004 Oryx and Väli et al. 2004 Ibis


The two species may coexist • Various natural, seminatural and man-made grasslands used by both species in Estonia


Aims of the current study • How does agricultural landscape management influence spotted eagles? • How much management (i.e. financial support in EU terms) is needed at least? Treshold needed! – Habitat selection by A. pomarina (comparison of nests and random points) – Breeding success of A. pomarina (nests with vs without nestling) – Habitat selection by A. clanga (nests vs random points) – Current occurrence of A. clanga (present vs abandoned nest sites)


Hybrids were included in the data set of Aquila clanga • Habitats of mixed pairs more similar to those of A. clanga than those of A. pomarina • Typical scenario at an Estonian A. clanga nest site: A. clanga

x A. clanga

A. clanga

Hybrid

A. pomarina

x

x

x

A. pomarina

A. pomarina

A. pomarina

Lõhmus & Väli 2005, Oryx Väli et al. 2010, Biol. J. Linn. Soc.


Study samples • 23 nest sites of A. clanga from 1993 – 2012 • 241 nest sites of A. pomarina from 2010 – 2012

(analysis of general digital maps and agricultural database)

• 88 nest sites of A. pomarina from 2004 – 2006 (analysis based on field mapping of biotopes)


Landscape variables •

General landscape analysis (Estonian basic map, 1: 20 000; 1 km, 2 km and 5 km around the nest): – forest, bush, fields, natural grasslands, other open landscape types, marshes, peatlands, urban landscape

Analysis of managed biotopes (Estonian Agricultural Register Map of financially supported land units; 1 km, 2km and 5 km around the nest) – Cultural or “man-made” grasslands; no crops for >4 yrs – Natural and seminatural grasslands – Crop fields – Managed fallows

Detailed analysis of agricultural management (Field mapping; 1 and 2 km around the nest) – Cereal fields – Mowed grassland – Rape fields – Pastures – Vegetables – Unmanaged grassland – Fallows – Afforesting grassland


Statistics • Generalized Linear Mixed Models (GLMM) (function glmer of package lme4 in R)

– Dependent variable (binomial) – nest/random point, existing/abandoned nest site, nestling/no nestling – Independent fixed effect – landscape variables – Random effect – year and/or nest site

• Generalized Linear Models (GLM; logistic regression) in analysis of the remaining and extinct Greaters


Results


Greater Spotted Eagle Aquila clanga • General landscape analysis confirmed the preference to (semi-)natural grasslands in 2 km (P = 0.031) but not in 1 km (P = 0.081) or 5 km (P = 0.187) radius.


Presence of eagle

Presence 93-12, 1 km:

Total grasslands (ha)

Greater Spotted Eagle Aquila clanga

Random

Nest

Expected curve

Managed grasslands, total (ha)

Management threshold

In the table: P-values of significant factors in best models Managed biotope Presence 1993 – 2012 Presence in 2010 – 2012 (nests vs random points)

“Man-made” grasslands (Semi-)natural grasslands Total grasslands

(present vs abandoned)

1 km

2 km

5 km

1 km

2 km

5 km

0.030

0.031

0.031

0.018

0.018

0.029


Presence of eagle

Presence 93-12, 1 km:

Total grasslands (ha)

Greater Spotted Eagle Aquila clanga

Random

Nest Managed grasslands, total (ha)

In the table: P-values of significant factors in best models

Managed biotope

“Man-made” grasslands (Semi-)natural grasslands Total grasslands

Presence 1993 – 2012

Presence in 2010 – 2012

(nests vs random points)

(present vs abandoned)

1 km

2 km

5 km

1 km

2 km

5 km

0.030

0.031

0.031

0.018

0.018

0.029


Presence of eagle

Presence 93-12, 2 km:

Total grasslands (ha)

Greater Spotted Eagle Aquila clanga

Random

Nest Managed grasslands, total (ha)

In the table: P-values of significant factors in best models

Managed biotope

“Man-made” grasslands (Semi-)natural grasslands Total grasslands

Presence 1993 – 2012

Presence in 2010 – 2012

(nests vs random points)

(present vs abandoned)

1 km

2 km

5 km

1 km

2 km

5 km

0.030

0.031

0.031

0.018

0.018

0.029


Total grasslands (ha)

Presence 10-12, 1 km:

Remaining of the eagle

Greater Spotted Eagle Aquila clanga

Abandoned

Present Managed grasslands, total (ha)

In the table: P-values of significant factors in best models

Managed biotope

“Man-made” grasslands (Semi-)natural grasslands Total grasslands

Presence 1993 – 2012

Presence in 2010 – 2012

(nests vs random points)

(present vs abandoned)

1 km

2 km

5 km

1 km

2 km

5 km

0.030

0.031

0.031

0.018

0.018

0.029


Presence of eagle

Presence, 1 km:

Manmade grasslands (ha)

Lesser Spotted Eagle A. pomarina

Random

Nest Managed grasslands, total (ha)

In the table: P-values of significant factors in best models

Managed biotope

“Man-made” grasslands (Semi-)natural grasslands Rotated crops (cereals, etc.)

Presence

Breeding success

(nests vs random points)

(Nestling or not)

1 km

2 km

5 km

1 km

2 km

5 km

<0.001

0.001

<0.001

0.018

0.043

<0.001

<0.0001

0.010 0.018


Presence of eagle

Breeding success, 5 km:

Manmade grasslands (ha)

Lesser Spotted Eagle A. pomarina

Successful pair

Unsuccessful Nest pair

Man-made grasslands (ha)

In the table: P-values of significant factors in best models

Managed biotope

“Man-made” grasslands (Semi-)natural grasslands Rotated crops (cereals, etc.)

Presence

Breeding success

(nests vs random points)

(Nestling or not)

1 km

2 km

5 km

1 km

2 km

5 km

<0.001

0.001

<0.001

0.018

0.043

<0.001

<0.0001

0.010 0.018


Lesser Spotted Eagle A. pomarina • Negative effect of rape fields on breeding success

P Rape fields

0.01

Year 2005

0.98

Year 2006

0.78

2005 * Rape

0.05

2006 * Rape

0.02

Note: sample size was smaller in this analysis – take marginal P-values more seriously!


Conclusions • Greater Spotted Eagle – Territories established in 1993 – 2012 in places, which are rich of natural grasslands and managed natural and man-made grasslands within 2 km around the nest – Survived in 2010 – 2013 where there are more man-made grasslands within 5 km around the nest. Management treshold hard to determine.


Conclusions • Lesser Spotted Eagle – Select places with managed grasslands and rotational crop fields. Effect too weak to determine a treshold for management – Hard to find effects of agricultural management on breeding success. The negative effect of rape is most conspicuous.


What next? • What biotopes are eagles actually using? – Observations – Telemetry


Thanks! Help in the field:

Financial support:

Raivo Endrekson, Tarmo Evestus, Kristo Lauk, Riho M채nnik, Renno Nellis, Ain Nurmla, Pauli Saag, Urmas Sellis and Indrek Tammek채nd

Estonian Fund for Nature

Photos: I thank myself, except for photos of a vole, frog and rape field, which were stolen from the Internet :)


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