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

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 â&#x20AC;˘ 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 â&#x20AC;&#x201C; 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 :)