Research Article |
Corresponding author: Konstantinos Poirazidis ( ecopoira@yahoo.gr ) Academic editor: Romain Julliard
© 2017 Konstantinos Poirazidis.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Poirazidis K (2017) Systematic Raptor Monitoring as conservation tool: 12 year results in the light of landscape changes in Dadia-Lefkimi-Soufli National Park. Nature Conservation 22: 17-50. https://doi.org/10.3897/natureconservation.22.20074
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Dadia-Lefkimi-Soufli National Park forms part of the Natura 2000 network in a region of Greece and represents one of the most diverse landscapes for raptors (birds of prey) breeding in Europe. It is adjacent to Bulgaria and Turkey and is a renowned biodiversity hotspot. WWF Greece established a Systematic Raptor Monitoring scheme in this area in 2001.This study summarises the results of the first 12 years of monitoring in the National Park. Overall, 25 to 27 raptor species were recorded by pooling data, of which20 species reproduced in the National Park. Raptors with continuous presence in the National Park exhibited stable, species-specific inter-annual variation. An average of 348±15.4 raptor territories were distributed throughout the National Park for all species. The Common buzzard (Buteo buteo) and the Short-toed eagle (Circaetus gallicus) were the most common species year-round, followed by the Lesser-spotted eagle (Clanga pomarina) and Booted eagle (Aquila pennata). The Long-legged buzzard (Buteo rufinus), Honey buzzard (Pernis apivorus) and Egyptian vulture (Neophron percnopterus) exhibited a noticeable drop in population numbers over the study period. A significant new entry was the re-appearance of the White-tailed eagle (Haliaeetus albicilla), which was recorded breeding again in the region after a 21-year absence. Species trends, along with their ecological traits, are discussed with respect to landscape changes in Dadia NP and minimum viable population and territory thresholds are proposed to outline essential conservation issues. Although a multi-year balance of the total number of occupied territories for all species was recorded, the number of common species increased compared to specialist species which had smaller, declining populations. The abandoning of traditional livestock farming, which induces an increase in closed-canopy forest coverage, might have led to the decline of the Lesser-spotted eagle, Long-legged buzzard and Honey buzzard numbers. Additional pressure is added from specialist forest dwelling raptors which are favoured by this change in habitat. The results of this study are expected to provide useful insights to facilitate conservation and management decisions about raptors and their habitat in this region.
birds of prey, population trends, modelling, GAM, Greece, conservation
Although Dadia-Lefkimi-Soufli National Park (Dadia NP) was established in 2003, it has had protected reserve status since 1980 as a result of its high ornithological value (
Although the landscape of Dadia NP remains heterogeneous and diverse (
Therefore, the current study aimed to: (i) assess the six monitoring surveys (March to August 2001–2005 and in 2012) completed in Dadia NP since 2001 by exploring the relative variation in the number of raptor territories in this region and (ii) model population trends of raptors from 2001 to 2012, to identify key conservation issues and explore which species are in need of immediate action. These results were expected to show the importance of SRM as a conservation strategy in the study region and as a protocol for evaluating variations in raptor numbers from which to develop focused processes to assess the drivers of these variations.
Dadia NP is located in the Evros Prefecture of Greece (N40°59" to 41°15"N, E26°19" to E26°36'), forming part of the south-eastern Rhodope mountains, bordering with Turkey in the east. The area includes two strictly protected core areas, encompassing a total of 7290ha. The altitude of the area ranges between 10m and 654m. Including the surrounding buffer zone, the area encompasses 35170ha (
In general, three main sampling methods are used for the census of breeding raptors: (i)line transects for surveying small areas on either side of a road; (ii)point count surveys in specified areas around fixed points and (iii)territory mapping (
Due to the topography of the area, good vantage points were limited and definitive vantage points were selected using the following criteria: (i) the point ensured the best and widest view of all neighbouring hillsides; (ii) the total area surveyed from vantage points included all main habitat types in proportion to their availability; (iii) the points were distributed equally over the entire study area, without habitat-bias towards plots with already known high raptor presence; (iv) access time to vantage points from the nearest road was short and (v) Black vulture colonies were avoided to reduce disturbance. Road transects were selected based on the following criteria: (i) how they complemented vantage points and, especially, for coverage of valley areas, where the positioning of adequate vantage points was not possible and (ii) to obtain the maximum coverage of the reserve by the two methods. Each survey was completed by two observers who alternated at sampling sites to reduce observer bias.
Details of the SRM scheme, describing both spatial and temporal parameters, are provided in
The total number of raptor species, along with the total number of individuals of each species, was recorded each year, along with details on the vantage point, transect and monitoring season. The total number of observations for each species was also recorded in a similar manner. To standardise differences in raptor numbers between years, the percentage of all recorded observations for each raptor species was calculated in relation to the total raptor observations in each monitoring year.
The number of territories was estimated using three standard steps to allow meaningful comparison. In Step 1, the observation data were entered in seven different ArcGIS layers: general flights, territorial observations, landings, synchronous observations, nest areas, meeting points and meeting point flights. The number of individuals, species, age, sex and different raptor activities were also recorded in an Access database that was interconnected with the GIS layers of Dadia NP. In Step 2, each territory was estimated independently for each vantage point and each road transect (representing 34 discrete sampling plots). When territories extended beyond the boundaries of discrete plots (continuing on to neighbouring plots), further analysis reshaped the polygon limits, creating new ones in a progressive process in which the recordings of each subsequent month in the same year were used to correct previous estimations (for details, see
Breeding territories were classified as: “confirmed” or “possible.” The classification “possible” was used when it was not possible to confirm with absolute certainty that the observations were obtained from separate individuals that maintained a separate territory. At the end, the final number of territories for each species was calculated by adding 50% of possible territories to the confirmed values (Palma et al. 2004).
Inter-annual variation in the relative number of raptor territories was explored by using the first SRM year as the starting point, appointing it with a value of 1. Then, for all subsequent monitoring years, a number was produced showing the relative difference in the number of territories per species in relation to the baseline value of 1 (
To explore the population trends of raptors, two approaches were implemented. First, the non-parametric and distribution-free test of Mann-Kendall (MK) was applied to the annual SRM values for the number of raptor territories to statistically determine whether there was a monotonic upward or downward trend of the variable of interest over time (
GAMs are actually flexible extensions of GLMs. In GAMs, the linear equation predictors that are associated with the GLMs are replaced by a more general additive predictor which allows the change in abundance over time to follow any smooth curve and not just a linear form (
GAMs are also used to separate actual underlying trends from short-term fluctuations. However, the precise point where a signal is interpreted as an irregular fluctuation, rather than a long-term trend, is poorly defined; thus, for each point, a framework to delineate noise from trends must be generated (
A number of diversity indices was also calculated for the raptor community in Dadia NP, following
The Osprey (Pandion haliaetus), Hen harrier (Circus cyaneus) and Red kite (Milvus milvus) were observed in Dadia NP, but were excluded from the analyses because they are currently, at least, non-breeders in the area. Similarly, the Black kite (Milvus migrans) was excluded from population trend analyses as it occupied territories close to Dadia NP, but did not breed inside the NP. The Western marsh harrier (Circus aeruginosus) was also excluded from the analysis, as it was absent during the first year, only establishing territories in the final year of monitoring. The colonial vulture species Griffon vulture (Gyps fulvus) and Cinereous vulture (Aegypius monachus) were also observed, but excluded from all analyses, as they form colonies and undertake common and long distance flights for foraging and do not present a strict territorial behaviour similar to other raptors. Finally, species that were sporadically recorded across years (Imperial eagle (Aquila heliaca), Lanner falcon (Falco biarmicus) and White-tailed Eagle were not included in this analysis.
Dadia NP was monitored from March to August 2001–2005 and in 2012 (i.e. totalling six censuses) within the framework of the SRM. A total of 23 raptors that form territories were recorded over all breeding seasons (Table
The number of Egyptian vulture territories was counted and evaluated in the SRM. Due to the rapid population decline of this species in the study region (and also in SE Europe), specific additional monitoring schemes were implemented from 2009 to 2017 in Dadia NP. The aim was to secure the Egyptian vulture survival in Greece and Bulgaria. More details are included in the official project’s website The Return of Neophron (http://www.lifeneophron.eu/en/index.html).
One-way ANOVA tests indicated that in a species-specific context, the presence of raptors was stable between monitoring years (25.17±1.47, F(4.1)=2.172, p=0.465). This pattern was similar in the whole NP and at vantage point plots (24.83±1.47, F(2.3)=0.316, p=0.750) and along road-transect plots (20.67±1.37, F(3.2)=0.549, p=0.697).
The most common species were the Common buzzard, Short-toed eagle and Lesser-spotted eagle, with an average relative abundance of 29.72%, 23.38% and 5.02% of all raptor species per monitoring year. All other species had a relative abundance of less than 3% per monitoring year (Table
The relative abundance of the Egyptian vulture was 4.8% (range: 3.87–5.87%) in 2001–2005, but dropped to 1.89% in 2012, indicating a rapid decline in the number of breeding territories over the course of a decade. In addition, the presence of the Long-legged buzzard decreased by 70% from 2001 to 2012 (Table
Relative frequency of raptors recorded during each Systematic Raptor Monitoring year in Dadia-Lefkimi-Soufli National Park. Percentages are calculated from the total of individuals observed from March to August 2001–2005 and in 2012. Data are shown in a decreasing value-order with respect to the first year of observation.
Species of raptors | 1st SRM year (2001) |
2nd SRM year (2002) |
3rd SRM year (2003) |
4th SRM year (2004) |
5th SRM year (2005) |
6th SRM year (2012) |
---|---|---|---|---|---|---|
Buteo buteo | 40.07 | 27.64 | 26.55 | 27.11 | 29.39 | 27.58 |
Circaetus gallicus | 20.61 | 25.07 | 26.19 | 24.07 | 22.90 | 21.47 |
Clanga pomarina | 4.49 | 5.79 | 4.18 | 5.75 | 4.81 | 5.13 |
Neophron perncopterus | 4.23 | 4.88 | 3.87 | 5.87 | 5.01 | 1.89 |
Aquila pennata | 3.97 | 3.49 | 3.78 | 3.19 | 2.99 | 4.65 |
Pernis apivorus | 3.25 | 3.49 | 2.63 | 1.17 | 2.11 | 2.46 |
Accipiter nisus | 2.73 | 3.03 | 2.41 | 1.21 | 1.52 | 2.74 |
Falco tinnunculus | 1.83 | 1.55 | 0.91 | 2.04 | 1.40 | 1.09 |
Accipiter gentilis | 1.80 | 2.29 | 1.08 | 0.91 | 1.60 | 1.96 |
Aquila chrysaetos | 1.53 | 1.39 | 1.06 | 1.72 | 1.84 | 0.96 |
Buteo rufinus | 1.01 | 0.61 | 0.53 | 0.64 | 0.72 | 0.28 |
Falco subbuteo | 0.60 | 0.63 | 0.27 | 0.34 | 0.30 | 1.30 |
Aquila heliaca | 0.37 | 0.11 | 0.09 | 0.01 | ||
Falco biarmicus | 0.37 | 0.00 | ||||
Milvus migrans | 0.49 | 0.83 | 0.22 | 0.77 | 0.81 | 1.09 |
Falco peregrinus | 0.26 | 0.04 | 0.18 | 0.58 | 0.41 | 0.28 |
Accipiter brevipes | 0.26 | 0.26 | 0.13 | 0.04 | 0.21 | 0.24 |
Circus aeroginosus | 0.04 | 0.09 | 0.03 | 0.17 | 0.72 | |
Circus cyaneus | 0.01 | 0.04 | ||||
Circus pygargus | 0.01 | 0.01 | 0.09 | |||
Haliaeetus albicilla | 0.04 | 0.21 | 0.74 | |||
Milvus milvus | 0.02 | |||||
Falco vespertinus | 0.09 |
The Booted eagle and Golden eagle (Aquila chrysaetos) displayed negative values in 2004 (SRM year 4); however, the population had re-established by 2012 (SRM year 6) to similar levels as in 2001 (SRM year 1) (Figure
Relative variation in the territory numbers of eagles in Dadia-Lefkimi-Soufli National Park during the Systematic Raptor Monitoring surveys (March to August 2001–2005 and in 2012).
Buzzards presented two opposing trends in the relative number of territories. The Common buzzard occupied more territories across all survey years, with a relative increase of 11.5% (Table
With respect to hawks, the number of Sparrowhawk (Accipiter nisus) territories decreased from 2001 (SRM year 1) to 2012 (SRM year 6) (Figure
The diversity of the raptor assemblage in Dadia NP decreased in the region over the study period based on all three indices (Shannon, Simpson and Invert-Simpson) (Figure
Relative variation in the number of raptor territories in the Dadia-Lefkimi-Soufli National Park during the Systematic Raptor Monitoring surveys from March to August 2001–2005 and in 2012. Calculations were made in relation to a “baseline value,” with the number of territories in year 1 being assigned the value of 1. Data are shown in decreasing value-order with respect to total variation (%).
Species of raptors | 1st SRM year (2001) “baseline value” |
2nd SRM year (2002) |
3rd SRM year (2003) |
4th SRM year (2004) |
5th SRM year (2005) |
6th SRM year (2012) |
Total Variation (%) |
---|---|---|---|---|---|---|---|
Falco peregrinus | 1 | 0.25 | 1.50 | 1.50 | 1.50 | 1.75 | 75.0 |
Falco subbuteo | 1 | 1.38 | 0.54 | 1.31 | 1.08 | 1.46 | 46.2 |
Accipiter brevipes | 1 | 2.40 | 1.60 | 0.40 | 1.20 | 1.40 | 40.0 |
Accipiter gentilis | 1 | 0.97 | 0.87 | 1.03 | 1.26 | 1.24 | 23.7 |
Circaetus gallicus | 1 | 1.27 | 1.17 | 1.11 | 1.30 | 1.22 | 22.2 |
Buteo buteo | 1 | 1.17 | 1.14 | 1.02 | 1.11 | 1.11 | 11.4 |
Aquila pennata | 1 | 0.98 | 0.88 | 1.02 | 1.00 | 1.05 | 4.9 |
Clanga pomarina | 1 | 1.21 | 1.09 | 1.21 | 1.29 | 1.03 | 2.9 |
Aquila chrysaetos | 1 | 1.13 | 0.88 | 1.25 | 1.38 | 1.00 | 0.0 |
Accipiter nisus | 1 | 0.81 | 0.86 | 0.76 | 0.90 | 0.78 | -22.2 |
Falco tinnunculus | 1 | 0.90 | 1.00 | 1.26 | 1.45 | 0.71 | -29.0 |
Pernis apivorus | 1 | 0.95 | 0.81 | 0.65 | 0.86 | 0.54 | -45.6 |
Neophron percnopterus | 1 | 1.05 | 0.86 | 1.09 | 0.86 | 0.45 | -54.5 |
Buteo rufinus | 1 | 0.86 | 0.86 | 0.86 | 1.14 | 0.43 | -57.1 |
Circus aeruginosus | 0.00 | 1.00 | 1.00 | 0.00 | 2.00 | 6.00 | 500.0 |
Total territory variation | 1 | 1.07 | 1.04 | 1.01 | 1.12 | 1.02 | 2.1 |
Relative variation in the number of territories of buzzards in Dadia-Lefkimi-Soufli National Park during the six Systematic Raptor Monitoring surveys (March to August 2001–2005 and in 2012).
Relative variation in the number of territories of falcons in Dadia-Lefkimi-Soufli National Park during the six Systematic Raptor Monitoring surveys (March to August 2001–2005 and in 2012).
Relative variation in the number of territories of hawks in Dadia-Lefkimi-Soufli National Park during the six Systematic Raptor Monitoring surveys (March to August 2001–2005 and in 2012).
Relative variation in the number of territories of Egyptian vultures in Dadia-Lefkimi-Soufli National Park during the six Systematic Raptor Monitoring surveys (March to August 2001–2005 and in 2012).
Three species exhibited noticeable overall increases in their presence in Dadia NP from 2001 to 2012; namely, the Common buzzard, the Short-toed eagle and the Northern goshawk. In contrast, four species exhibited noticeable decreases; namely, the Common kestrel, the Egyptian vulture, the Eurasian sparrowhawk and the Honey buzzard. A further two species displayed moderate increases; namely, the Western marsh harrier and the Eurasian hobby. Four species showed marginal upward trends; namely, the Peregrine falcon, the Levant sparrowhawk, the Booted eagle and the Lesser-spotted eagle. Two species displayed moderate decreases; namely, the Golden eagle and the Long-legged buzzard. (See Table
The population trends of 14 raptors were modelled. These species had a continuous presence, with active territories in the study area across all survey years (Table
Although the MK test did not reveal statistically significant monotic trends, it provided valuable information on species trends (positive or negative), depending on the sign of the Sen slope value. This result was obtained due to the time series being short. Furthermore, a monotonic line cannot always fit significant fluctuations. In comparison, the more flexible GAMs confirmed that time had a significant effect on population change, with the preliminary trend for the study period being graphically presented using the smoothing technique.
The Short-toed eagle was the only eagle with an increasing trend. The MK test showed an upward trend (though not significant), whereas the GAM showed a significant relative change in the number of territories over time, with a good fit (Table
With respect to buzzards, only the Common buzzard had a stable trend (MK: tau= 0.066, p=1). The Long-legged buzzard and Honey buzzard showed decreasing MK slopes (Sen slope: -0.166 and -2.6, respectively). The variation in the number of Buzzard territories versus monitoring years was highly significant, with a good fit when using GAMs (Table
The trend recorded for hawks was significant when using GAMs (Northern goshawk: t=69.240, p<0.01, Eurasian sparrowhawk: t=24.292, p<0.0001, Levant sparrowhawk: t=14.990, p<0.05), with a robust fit (Table
The Common kestrel had a negative population trend. The MK slope was not significant, but positive for this species (tau= 0.138, p=0.848). This result was possibly due to a strong increase during the initial years of monitoring (Figure
Out of all documented raptor species, the Egyptian vulture demonstrated the greatest population decline (Tables
With respect to the overall number of raptor territories, a small overall increase was detected (Table
Generalised Additive Models fitting the Systematic Raptor Monitoring values for each survey year of the number of raptor territories in Dadia-Lefkimi-Soufli National Park (March to August 2001–2005 and in 2012). Results of Linear GAMs and GAMs with cubic and cyclic cubic smoothing splines are shown.
Species of raptors | Linear GAM Family: Gaussian Link function: Identity |
GAM cr Cubic regression smoothing splines Family: Gaussian Link function: Identity |
GAM ccr Cyclic cubic regression smoothing splines Family: Gaussian Link function: Identity |
|||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
R2 adj | Deviance explained | GCV | AIC | R2 adj | Deviance explained | GCV | AIC | R2 adj | Deviance explained | GCV | AIC | |
EAGLES | ||||||||||||
Circaetus gallicus | -0.072 | 14.2% | 19.729 | 36.05 | 0.998 | 100% | 0.180 | -2.74 | 0.996 | 99.9% | 0.2685 | -0.34 |
Aquila chrysaetos | -0.25 | 0.02% | 1.015 | 18.25 | 0.131 | 43.1% | 0.861 | 16.32 | 0.244 | 54% | 0.807 | 15.51 |
Clanga pomarina | -0.215 | 2.82% | 7.045 | 29.87 | 0.477 | 67.6% | 3.921 | 25.09 | 0.375 | 61.6% | 4.728 | 26.16 |
Aquila pennata | 0.078 | 26.3% | 2.039 | 22.43 | 0.078 | 26.3% | 2.039 | 22.43 | 0.032 | 3.25% | 1.712 | 22.06 |
BUZZARDS | ||||||||||||
Buteo buteo | -0.2 | 3.99% | 99.626 | 45.77 | 0.688 | 92.99% | 91.541 | 35.85 | 0.676 | 92.7% | 95.525 | 36.05 |
Buteo rufinus | 0.47 | 57.6% | 0.556 | 14.64 | 0.911 | 96.8% | 0.209 | 3.52 | 0.911 | 96.7% | 0.198 | 3.63 |
Pernis apivorus | 0.629 | 70.4% | 13.879 | 33.94 | 0.852 | 96.1% | 17.003 | 27.13 | 0.629 | 70.4% | 13.879 | 33.94 |
SPARROWHAWKS | ||||||||||||
Accipiter gentilis | 0.369 | 49.5% | 8.303 | 30.861 | 0.942 | 98.5% | 2.406 | 15.132 | 0.629 | 70.4% | 13.879 | 33.943 |
Accipiter nisus | 0.078 | 26.3% | 14.327 | 34.13 | 0.078 | 26.3% | 14.329 | 34.13 | -0.019 | -1.95% | 12.683 | 34.08 |
Accipiter brevipes | -0.243 | 0.58% | 5.157 | 28.00 | 0.893 | 97.8% | 1.713 | 11.13 | 0.887 | 97.6% | 1.808 | 11.48 |
FALCONS | ||||||||||||
Falco tinnunculus | -0.092 | 12.6% | 27.32 | 38.00 | 0.998 | 99.9% | 0.231 | -0.66 | 0.998 | 99.9% | 0.210 | -0.70 |
Falco subbuteo | 0.015 | 21.2% | 7.189 | 29.99 | 0.015 | 21.2% | 7.189 | 29.99 | 0.005 | 0.5% | 5.805 | 29.39 |
Falco peregrinus | 0.24 | 39.2% | 1.368 | 20.04 | 0.24 | 39.2% | 1.368 | 20.04 | 0.249 | 40.6% | 1.367 | 19.99 |
VULTURES | ||||||||||||
Neophron perncopterus | 0.801 | 84.1% | 2.551 | 23.78 | 0.819 | 86.6% | 2.495 | 23.32 | 0.813 | 85.8% | 2.526 | 23.50 |
TOTAL TERRITORIES | ||||||||||||
Total number of territories in Dadia NP | -0.241 | 0.71% | 436.1 | 20.04 | 0.903 | 98% | 130.97 | 37.16 | 0.897 | 97.8 | 139.82 | 37.55 |
Inter-annual variation in the numbers of territories for Short-toed eagle and Golden eagle in Dadia-Lefkimi-Soufli National Park fitting Generalised Additive Models. Population trend modelling is also shown for each species, with cyclic cubic regression (cc) splines used as smoothing terms. a Variation in the number of Short-toed eagle territories fitting a GAM b Predictive GAM for the Short-toed eagle with smoothed terms (cc splines) c Variation in the number of Golden eagle territories fitting a GAM d Predictive GAM for the Golden eagle with smoothed terms (cc splines).
Relative frequency in the number of raptor territories in Dadia-Lefkimi-Soufli National Park in 2001 and in 2012. Percentages were calculated from the total number of territories per year. Percentage change variation was based on the difference between the first and the last year of the Systematic Raptor Monitoring scheme. Absolute territory numbers per species are shown for both 2001 and 2012. Data are shown in decreasing value-order with respect to the overall percentage variation change.
Birds of prey species | Absolute number of territories in 2001 | Absolute number of territories in 2012 | Relative territory frequency in 2001 (%) | Relative territory frequency in 2012 (%) | Percentage (%) variation change between 2001 and 2012 |
---|---|---|---|---|---|
Buteo buteo | 110 | 122.5 | 32.93 | 35.92 | 2.99 |
Circaetus gallicus | 31.5 | 38.5 | 9.43 | 11.29 | 1.86 |
Accipiter gentilis | 19 | 23.5 | 5.69 | 6.89 | 1.20 |
Circus aeruginosus | 0 | 3 | 0.00 | 0.88 | 0.88 |
Falco subbuteo | 6.5 | 9.5 | 1.95 | 2.79 | 0.84 |
Falco peregrinus | 2 | 3.5 | 0.60 | 1.03 | 0.43 |
Accipiter brevipes | 2.5 | 3.5 | 0.75 | 1.03 | 0.28 |
Aquila pennata | 20.5 | 21.5 | 6.14 | 6.30 | 0.17 |
Clanga pomarina | 17 | 17.5 | 5.09 | 5.13 | 0.04 |
Aquila chrysaetos | 4 | 4 | 1.20 | 1.17 | -0.02 |
Buteo rufinus | 3.5 | 1.5 | 1.05 | 0.44 | -0.61 |
Falco tinnunculus | 15.5 | 11 | 4.64 | 3.23 | -1.41 |
Neophron percnopterus | 11 | 5 | 3.29 | 0.47 | -1.83 |
Accipiter nisus | 36 | 28 | 10.78 | 8.21 | -2.57 |
Pernis apivorus | 28.5 | 15.5 | 8.53 | 4.55 | -3.99 |
Inter-annual variation in the numbers of territories for Lesser-spotted eagle and Booted eagle territories in Dadia-Lefkimi-Soufli National Park fitting Generalised Additive Models. Population trend modelling is also shown for each species with cyclic cubic regression (cc) splines used as smoothing terms. a Variation in the number of Lesser-spotted eagle territories fitting a GAM b Predictive GAM for the Lesser-spotted eagle with smoothed terms (cc splines) c Variation in the number of Booted eagle territories fitting a GAM d Predictive GAM for the Booted eagle with smoothed terms (cc splines).
Inter-annual variation in the number of buzzard territories in Dadia-Lefkimi-Soufli National Park fitting Generalised Additive Models. Population trends modelling is also shown for each species with cubic regression (cr) or cyclic cubic regression (cc) splines used as smoothing terms, depending on lowest AIC in each case. a Variation in the number of Common buzzard territories fitting a GAM b Predictive GAM for the Common buzzard with smoothed terms (cc splines) c Variation in the number of Long-legged buzzard territories fitting a GAM d Predictive GAM for the Long-legged buzzard with smoothed terms (cr splines) e Variation in the number of Honey buzzard territories fitting a GAM f Predictive GAM for Honey buzzard with smoothed terms (cr splines).
Inter-annual variation in the number of hawk territories in Dadia-Lefkimi-Soufli National Park fitting Generalised Additive Models. Population trend modelling is also shown for each species with cubic regression (cr) or cyclic cubic regression (cc) splines used as smoothing terms, depending on lowest AIC in each case.a Variation in the number of Northern goshawk territories fitting a GAM b Predictive GAM for the Northern goshawk with smoothed terms (cc splines) c Variation in the number of Eurasian sparrowhawk territories fitting a GAM d Predictive GAM for the Eurasian sparrowhawk with smoothed terms (cr splines) e Variation in the number of Levant sparrowhawk territories fitting a GAM f Predictive GAM for the Levant sparrowhawk with smoothed terms (cr splines).
Inter-annual variation in the number of falcon territories in Dadia-Lefkimi-Soufli National Park fitting Generalised Additive Models. Population trends modelling is also demonstrated for each species with cubic regression (cr) splines used as smoothing terms. a Variation in the number of Common kestrel territories fitting a GAM b Predictive GAM for the Common kestrel with smoothed terms (cr splines) c Variation in the number of Eurasian hobby territories fitting a GAM d Predictive GAM for the Eurasian hobby with smoothed terms (cr splines) e Variation in the number of Peregrine falcon territories fitting a GAM f Predictive GAM for the Peregrine falcon with smoothed terms (cr splines).
Inter-annual variation in the number of Egyptian vulture in Dadia-Lefkimi-Soufli National Park fitting Generalised Additive Models. Population trend modelling is also shown for the species with cubic regression (cr) splines used as smoothing terms. a Variation in the number of Egyptian vulture territories fitting a GAM b Predictive GAM for the Egyptian vulture with smoothed terms (cr splines).
Inter-annual variation in the number of overall raptor territories in Dadia-Lefkimi-Soufli National Park fitting Generalised Additive Models. Population trends modelling is also demonstrated for the whole number of territories with cubic regression (cr) splines used as smoothing terms. a Variation in the number of overall raptor territories fitting a GAM b Predictive GAM for overall raptor territories with smoothed terms (cr splines).
Monitoring is an essential tool for effective nature conservation and management. Both long-term trends and the present status of populations allow sound management programmes to be formulated (
Globally, the monitoring effort of raptors tends to focus on nest location and the observation of individuals (
A total of 27 diurnal raptor species were recorded in Dadia NP during the breeding season, 20 of which breed in the NP regularly. Three different diversity indices calculated for the raptor assemblage (Shannon, Simpson, Invert-Simpson) showed that raptors exhibited high diversity in the NP. These values had the highest ranking compared to values for raptors in other areas (
However, over the 12-year period (from SRM1 to SRM 6), raptor diversity declined. All diversity values reached their lowest point in the final SRM year (2012) (Figure
However, it is also important to determine whether this decline in overall raptor diversity is actually due natural fluctuation processes or whether there is actually a consistent decline in rare and more specialist species requiring management action. A definite answer could only be provided following the long-term implementation of the SRM scheme. Such information would clarify whether the natural fluctuation process will be reversed or whether the decrease in diversity will continue due to intra-specific competition, landscape change and anthropogenic pressure. In particular, species with smaller numbers, less competitive mechanisms and more specialised habitat requirements might be at risk (
Overall, Dadia NP has a generally stable number of territories, with a small annual increase (Figure
The Short-toed eagle is a specialist predator with a narrow niche diet of reptiles (
With respect to eagles, the Booted eagle demonstrated robust population stability, whereas the Golden eagle and Lesser-spotted eagle exhibited contrasting trends. Both species exhibited overall stability, with similar values being obtained in the first and last SRM years; however, values fluctuated irregularly in the intervening years. In particular, 2003 was a poor year for eagle abundance in Dadia NP (Figures
The Golden eagle and Lesser-spotted eagle presented identical trends (Figures
A recent, noticeable, change in modern agricultural practices in the region of Dadia NP is the monoculture of Helianthus (Helianthus annuus), due to contract agriculture. Contract farming involves agricultural production being carried out on the basis of an agreement between the buyer and farm producers, where the buyer specifies the quantity required and the price, with the farmer agreeing to deliver at a future date. Similar changes in Estonia have caused problems for eagles that forage in open areas during the breeding period, these eagles decreasing due to Helianthus farming, including the Lesser-spotted eagle (
The Common buzzard is a generalist predator with a broad habitat niche (
The Honey buzzard and Long-legged buzzard are more specialist species and demonstrated negative population trends. Interestingly, in the bordering regions of Bulgaria, the Long-legged buzzard has not undergone any major decline for 20 years (
The Honey buzzard showed the largest population decrease of all the buzzard species in Dadia NP (Table
In contrast to the Eurasian sparrowhawk (Figure
The Levant sparrowhawk has a much lower population size in the study region (Table
The Common kestrel was the only falcon to exhibit decreasing trends in the Dadia NP (Figure
One of the most important and emblematic species for the region, the Egyptian vulture, is being subject to distinct decreasing population trends (Figure
A common concept in wildlife populations is that, under situations of pressure, limitation of resources, competition and habitat/landscape change, specialist species are the first to pay the price, due to their inability to adapt to rapid changes and have narrow niches (
Specialisation is an expected evolutionarily response to habitat stability (in space or time), whereas the generalist strategy is a response to the lack of stability of the environment (
The complex ecosystem of Dadia NP, along with its complex raptor assemblage, creates a highly dynamic system where raptors are influenced by competitive interactions and various environmental parameters at different ecological scales (
At present, five major conservation issues exist in the Dadia NP raptor assemblage:
The total number of occupied raptor territories in the NP appears to be stable over time, showing the viability of the ecosystem to host raptors; however, a parallel increase in common and generalist species has been observed and this may be causing a reduction in the number of territories occupied by the more specialist species with smaller populations.
The increase in homogenisation through forest encroachment on forest clearings that are no longer grazed and the change in the type of agricultural crops being planted through contract-farming, might be contributing to the decline in certain species, like the Lesser-spotted eagle, Long-legged buzzard and Honey buzzard.
Furthermore, the increase in certain forest dwelling species that favour the increase in the closed-canopy environment, such as the Northern goshawk, might also be placing more pressure on these declining species, including the Eurasian sparrowhawk and the Common kestrel, due to its greater competitive ability.
Except for raptor species with increasing and decreasing trends, some raptors exhibited relative stability, but with noticeable fluctuations, such as the Levant sparrowhawk, the Booted eagle and the Golden eagle. To determine whether the observed trends in these and all other raptor groups are indicative of normal population fluctuations or deviations from regularity, long-term monitoring is required to remove “noise.” Therefore, without doubt, the SRM in Dadia NP must be continued without interruption to enrich the time-series data and to optimise management in the decades to come.
The important anthropogenic pressure which has been recently identified by other studies, denoting the impact of illegal poisoning and collisions with wind turbines is an additional limiting factor on raptor populations.
This paper is based on work conducted through WWF Greece projects for the conservation of the Dadia-Lefkimi-Soufli National Park and was partly supported by the LIFE Nature project “Conservation of Birds of Prey in the Dadia Forest Reserve, Greece” (LIFE02NAT/GR/8497). We thank Stefan Schindler and Carlos Ruiz for coordinating and participating in the Systematic Raptor Monitoring scheme for many years, as well as Chiara Scandolara, Lise Pomarède, Elefterios Kakalis, Dimitris Bakaloudis, Chris Eastham, Hristo Hristov, Giorgos Catsadorakis and Javier Elorriaga for participating in the fieldwork. The work of EVS volunteers hosted by WWF Greece is also sincerely appreciated for their important support with data input. Special thanks are extended to Kostas Katselidis for support in developing R code for data analyses. We thank the reviewers Dr Stoyan Nikolov, Dr Yannis Matsinos and Dr Romain Julliard for providing constructive comments to improve the initial manuscript. Many thanks to Dr Vasileios Bontzorlos for providing constructive comments throughout the preparation of the manuscript and special thanks to Dr Gail Schofield for the review and linguistic editing of the text.