Accounting for differential migration strategies between age groups to monitor raptor
population dynamics in the eastern Black Sea flyway (Vansteelant et al. In 2nd review IBIS)
DRIES ENGELEN - [email protected]
Photo: Adrien Brun
One of the world’s largest bottlenecks for raptor migration
Based on ‘Raptors of the World’ (Bildstein, 2000)
Photo: Adrien Brun
Targeted monitoring Priority species, secondary species
Using morphological groups MonPalHen, Large Eagle, etc.
Quantity vs quality Ageing (& sexing) Photo: John Wright
Photo: Adrien Brun
Estimated from unidentified Targeted monitoring individuals (%) Species Priority species, secondary species Avg SD
Montagu’s Harrier 55,7 10,7
Pallid Harrier 50,5 11,1
Using morphological groups Western Marsh Harrier 0,2 0,1 MonPalHen, Large Eagle, etc. Black Kite 10,0 5,0
Barely mentioned (recorded?) in literature European Honey Buzzard 1,8 1,3
Booted Eagle 0,0 0,0
Quantity vs quality Short-toed Snake Eagle 0,0 0,0 Ageing (& sexing) Lesser Spotted Eagle 43,9 15,6
Photo: Adrien Brun
Estimated from unidentified Targeted monitoring individuals (%) Species Priority species, secondary species Avg SD
Montagu’s Harrier 55,7 10,7
Pallid Harrier 50,5 11,1
Using morphological groups Western Marsh Harrier 0,2 0,1 MonPalHen, Large Eagle, etc. Black Kite 10,0 5,0
European Honey Buzzard 1,8 1,3
Booted Eagle 0,0 0,0
Quantity vs quality Short-toed Snake Eagle 0,0 0,0 Ageing (& sexing) Lesser Spotted Eagle 43,9 Photo: John15,6 Wright
Photo: Adrien Brun
Age data is barely used in population trend analyses
However
1) Inexperienced juveniles often behave differently than experienced conspecifics (timing, route choice, response to environmental change).
(Kjellén 1992, 1998; Vansteelant et al. 2017)
Important reason to separate the 1794 juveniles variability in trends 24929 adults
Photo: Bart Hoekstra Age data is barely used in population trend analyses
However
2) Demographic changes may serve as early warning system for population change.
(Bednarz et al. 1990, Wright 2016)
Survival vs breeding success 1794 juveniles 24929 adults
Photo: Bart Hoekstra Selection of species
• Counted individuals per year > 1000 • Aged a decent number of individuals • Timing of both age groups passage falls within our count period
Aged in the field (%) Species Avg SD
Montagu’s Harrier 44,3 10,7
Pallid Harrier 49,5 11,1
Western Marsh Harrier 61,7 6,9
Black Kite 3,4 1,1
European Honey Buzzard 4,1 2,5
Booted Eagle 24,7 12,1
Short-toed Snake Eagle 45,8 10,3
Lesser Spotted Eagle 35,8 12,4 Photo: Adrien Brun Similar to the morphological groups, the age distribution is also based on the daily proportion of aged individuals
Percentage of world Juveniles Non-juveniles Totals World population* population passing through Species (breeding ind.) Batumi (%) Avg SD Avg SD Avg SD Min. Max.
Montagu’s Harrier 2491 1345 4436 1204 6927 1959 100.000 - 499.999 0,9 4,4
Pallid Harrier 747 505 744 407 1491 612 18.000 - 30.000 2,5 4,1
Western Marsh Harrier 2359 341 4130 871 6489 982 500.000 - 999.999 0,4 0,8
Black Kite 41.236 12.389 95.718 28.652 136.953 36.461 1.000.000 - 2.499.999 3,8 9,6
European Honey Buzzard 30.502 12.154 500.066 94.539 530.568 96.563 280.000 - 420.000 119,1 178,6
Booted Eagle 1435 442 5040 700 6475 665 149.000 - 188.000 2,7 3,4
Short-toed Snake Eagle 236 82 1192 110 1427 155 100.000 - 200.000 0,6 1,2
Lesser Spotted Eagle 1534 745 6181 882 7715 1462 40.000 - 60.000 10,3 15,5
* Source: Birdlife International Datazone Similar to the morphological groups, the age distribution is also based on the daily proportion of aged individuals
Percentage of world Juveniles Non-juveniles Totals World population* population passing through Species (breeding ind.) Batumi (%) Avg SD Avg SD Avg SD Min. Max.
Montagu’s Harrier 2491 1345 4436 1204 6927 1959 100.000 - 499.999 0,9 4,4
Pallid Harrier 747 505 744 407 1491 612 18.000 - 30.000 2,5 4,1
Western Marsh Harrier 2359 341 4130 871 6489 982 500.000 - 999.999 0,4 0,8
Black Kite 41.236 12.389 95.718 28.652 136.953 36.461 1.000.000 - 2.499.999 3,8 9,6
European Honey Buzzard 30.502 12.154 500.066 94.539 530.568 96.563 280.000 - 420.000 119,1 178,6
Booted Eagle 1435 442 5040 700 6475 665 149.000 - 188.000 2,7 3,4
Short-toed Snake Eagle 236 82 1192 110 1427 155 100.000 - 200.000 0,6 1,2
Lesser Spotted Eagle 1534 745 6181 882 7715 1462 40.000 - 60.000 10,3 15,5
* Source: Birdlife International Datazone Data 2011-2018 (Vansteelant et al. In 2nd review) daily totals; relative timing of passage; yearly totals European Honey Daily totals Relative timing Yearly totals Buzzard Pernis apivorus
Totals Non-juveniles Juvenil
No detectable trends in the number of non- juveniles, indicating a stable population.
Percentage of world population passing through the Batumi Too high variability in the number of juveniles Bottleneck 119,1 – 178,6% to detect moderate trends.
No change detected in phenology Non-juveniles precede juveniles Photo: Bart Hoekstra
Western Marsh Daily totals Relative timing Yearly totals Harrier Circus aeruginosus
Totals Non-juveniles Juveniles
No detectable trends, indicating a stable population
Percentage of world population passing through the Batumi Longest migration period of all study species Bottleneck 0,4 – 0,8%
No change detected in phenology Photo: Aki Aintila Lesser Spotted Daily totals Relative timing Yearly totals Eagle Clanga pomarina
Totals Non-juveniles Juveniles
No detectable trends, indicating a stable population
Percentage of world population passing through the Batumi Bottleneck 10,3 – 15,5%
No change detected in phenology Photo: Bart Hoekstra Booted Eagle Daily totals Relative timing Yearly totals Hieraaetus pennatus
Totals Non-juveniles Juveniles
Obscured by a seemingly stable population number, is a strong decline in the number of juveniles (-10% per year). Percentage of world population passing through the Batumi Bottleneck 2,7 – 3,4% Until 2018 there was even a significant increase in the number of non-juveniles (P < No change detected in phenology 0.05). Photo: Bart Hoekstra Montagu’s Harrier Daily totals Relative timing Yearly totals Circus pygargus
Totals Non-juveniles Juveniles
Too high variability to detect trends
Strong decline in number of juveniles with 17% Percentage of world population passing through the Batumi per year Bottleneck 0,9 - 4,4% Earliest migrant amongst study species
No change detected in phenology Photo: Bart Hoekstra
Pallid Harrier Daily totals Relative timing Yearly totals Circus macrourus
Totals Non-juveniles Juveniles
Variability too high in both age-classes to detect any trends
Percentage of world population passing through the Batumi Counting them remains necessary to know the Bottleneck 2,5 - 4,1% proportion of Montagu’s Harrier in ‘MonPalHen’
No change detected in phenology Photo: Bart Hoekstra Short-toed Snake Daily totals Relative timing Yearly totals Eagle Circaetus gallicus
Totals Non-juveniles Juveniles
Very small variability in the numbers of non-juveniles, shows a slightly increasing trend (+3% per year).
Percentage of world population passing through the Batumi Too high variablity in the number of juveniles to Bottleneck 0,6 – 1,2% detect any trends.
No change detected in phenology Latest migrant amongst study species Photo: Bart Hoekstra
Black Kite Daily totals Relative timing Yearly totals Milvus migrans
Totals Non-juveniles Juveniles
Clearly increasing population (+10% per year), mostly due to increasing numbers of non- juveniles (+11% per year). Percentage of world population passing through the Batumi Bottleneck Increase in juveniles only just significant since 3,8 – 9,6% 2018 (P = 0,05, +9% per year).
No change detected in phenology Photo: Bart Hoekstra Since 2000
Strong increase from 1000s to 30.000+ Black Kites overwintering at the Dudaim landfill in the Negev desert of Israel.
Similar situations in south-eastern Europe (Literák et al., 2017) and Turkey (Biricik & Karakaş, Photo: Richard 2011). Stein Strong connection Image: Daniel Berkowic Batumi-Negev Photo: Wim Bovens Shown by tracking studies (Daniel Berkowic, unpublished.) and the observation of a wing- tagged individual on our count station. Conclusion
• Most of the studied raptor populations are stable. European Honey Buzzard, Western Marsh Harrier, Booted Eagle, Lesser Spotted Eagle
• Clear increase in the numbers of Black Kite and Short-toed Snake Eagle, mostly as a result of increasing numbers of non-juvenile birds improved wintering conditions
• Stable totals of Montagu’s Harrier and Booted Eagle obscure the significant declines in the numbers of juvenile birds. problem at the breeding grounds
Photo: Bart Hoekstra Recommendations
• Targeted count strategy per observation point
• We can better understand population trends when we make an effort to document the different age classes and not just count totals.
• We strongly believe that open access data so that we can get a good overall idea of European raptor populations and better target conservation efforts.
• Tools available: trektellen, GBIF
Photo: Bart Hoekstra How can you contribute?
• Collaborations for research
• Become a counter or coordinator in the autumn count
• Become a member or make a donation
Photo: Bart Hoekstra Thank you for your attention!
Supported by: www.batumiraptorcount.org @BatumiRaptors facebook.com/batumiraptorcount Phenology