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 :)