Trends

Population trends of common birds

From the beginning of the monitoring period 2005-2013 a total of 215 species are registered or nearly 50% of the species in Bulgaria. In 2013 are registered 169 species which is the highest number up to now. Every year CBM participants register between 151 and 169 species. Amongst the species registered for the first time in 2013 are River Warbler (Locustella fluviatilis), White-tailed Eagle (Haliaeetus albicilla) and Griffon Vulture (Gyps fulvus).

The species registered during the CBM are classified in three main groups following the Pan-European Common Birds monitoring scheme (PECBM). They are divided according to the habitat types they occupy: farmland, forest, and “other” types for habitat species that are generalists and not related a particular habitat type or occupy more than habitat type.

The common bird index for Bulgaria for 2005-2013 shows a decline of bird populations with 21% for this period (Fig. 2). This fact is extremely alarming having in mind that the trend until 2012 was a decline with 12 %. This suggests increased impact of negatively influencing processes and trends of common birds.

 

In addition to the 38 species in the index we managed to assess the state of additional 21 species reaching a total of 59. This is the highest number of assessed species trends up to now which is a result of the long term data accumulation and increase of national coverage of the monitoring scheme. The trend categories are shown on fig. 3. It is obvious that the highest proportion of species have uncertain trend (53%), followed by moderate decline (22%), stable (10%) and steep decline (8%). The species in moderate and steep increase are just 7% of all. The high proportion of species with uncertain trend categories suggests the necessity for continuation of the monitoring scheme and accumulation of more data that would increase the species coverage.

There are several differences in the trends to 2012 including an increase of species with stable trend from 7% to 10%. However, the increasing species have dropped from 9% to 7% and the species in decline have dropped from 33 to 30%.

 

Farmland bird index

The majority of the farmland species in this group are with declining or uncertain trend. In the previous assessment for 2005-2012 farmland birds marked a decline with -11%, however in the current they continue the decline to -21% (Fig.4). The reasons for these changes are still unknown and there is an urgent need for specific well targeted studies.

Population trends of farmland birds are presented in the table below.

 

Table: Trends of farmland birds

			Total for Bulgaria
	Species name	Scientific name	Change   (%)	Sample    plots	Trend category
1	Eurasian Skylark	Alauda arvensis	-14,24	129	-
2	Common Starling	Sturnus vulgaris	-36,66	139	↓
3	Eurasian Tree Sparrow	Passer montanus	24,2	98	?
4	European Goldfinch	Carduelis carduelis	-65,97	96	↓↓
5	Woodchat Shrike	Lanius senator	-50,91	34	↓
6	White Stork	Ciconia ciconia	-61,16	96	↓
7	Common Kestrel	Falco tinnunculus	11,53	83	?
8	Common Quail	Coturnix coturnix	-64,36	90	↓
9	Common Pheasant	Phasianus colchicus	7,37	34	?
10	European Turtle Dove	Streptopelia turtur	-1,55	96	?
11	European Bee-eater	Merops apiaster	-14,65	96	↑
12	Eurasian Hoopoe	Upupa epops	-18,8	87	?
13	Crested Lark	Galerida cristata	-28,07	79	?
14	Barn Swallow	Hirundo rustica	-41,96	142	↓
15	Yellow Wagtail	Motacilla flava	-12,88	96	↓
16	Whinchat	Saxicola rubetra	-36,27	49	↓
17	European Stonechat	Saxicola torquata	-45,24	32	?
18	Marsh Warbler	Acrocephalus palustris	35,38	21	?
19	Eastern Olivaceous Warbler	Hippolais pallida	-56,71	29	?
20	Common Whitethroat	Sylvia communis	156,44	82	↑↑
21	Red-backed Shrike	Lanius collurio	-14,22	129	?
22	Lesser Grey Shrike	Lanius minor	-82,7	65	↓↓
23	Ortolan Bunting	Emberiza hortulana	35,9	53	?
24	Black-headed Bunting	Emberiza melanocephala	1,24	87	?
25	Corn Bunting	Miliaria calandra	-42,73	126	↓

 

Legend:

↑↑ Strong increase: increases significantly with more than 5% per year. Criterion: lower limit of confidence interval > 1.05

↑ Moderate increase: increases considerably but with insignificantly more than 5% per year. Criterion: 1.00 < lower limit of confidence interval < 1.05

- Stable: no significant increase or decline; the trend is certainly less than 5% per year. Criterion: confidence interval encloses 1.00 but lower limit > 0.95 and upper limit < 1.05

* Uncertain: no significant increase or decline but it is not certain if the trend is less than 5% per year. Criterion: confidence interval encloses 1.00 but lower limit < 0.95 and upper limit > 1.05

↓ Moderate decline: considerable decline but insignificantly more than 5% per year. Criterion: 0.95 < upper limit of confidence interval < 1.00

↓↓ Steep decline: declines significantly with more than 5% per year. Criterion: upper limit of confidence interval < 0.95

 

Amongst the species with negative trends are the Goldfinch and the Quail. Their trend is probably related to destruction of natural grassland and replacement of grain crops with rape. In the last years grassland areas have significantly decreased mainly because of their ploughing a result of direct payment from the Rural development programme (RDP). At the same time agri-environmental measures for HNV 4 in measure 214 “Agri-environmental” payments from the RDP are not popular enough amongst farmers. The lack of information for them, administrative challenges and lack of interest from large scale farmers for agri-environmental measures are amongst the main reason for the measures’ low uptake. There is a need for more active and large scale implementation of the measures related to conservation and restoration of natural grasslands and meadows. In addition there is a need for conservation and creation of suitable habitats for birds that could significantly contribute to improving population trends of common birds. It is necessary to assess the role of changing grain crops with technical ones like rape and the impact of land management intensification on farmland birds.

Significant decline is shown by the Lesser-grey Shrike population trend. The species uses relatively diverse habitat types with mosaic distribution, including farmland, grassland with trees and scrub. In some regions of the country there are significant changes in this habitat type such as scrub removal from grassland up to 100%.

The only species with stable trend in this group is the Skylark and the only one with strongly increasing trend is again the Common Whitethroat.

 

There is an urgent need for a targeted study on the species in decline to identify the reasons for their trends. In addition it is necessary to include a greater variety of habitat types including urban environment.

 

Population trends of forest birds

Forest habitat is still not well represented in the CBM survey plots, which limits assessing the state of forest birds. That is why it is difficult to assess the actual state of forest species because there are no or little data for species that are habitat specialists and the state of common birds cannot be representative for their trends. There is a need for an increased coverage of the monitoring in forest habitat to gain better understanding for real changes in this type of habitat especially for old broad leaved or coniferous forest.

The forest bird index varies throughout the years with about 10% staying stable or with insignificant changes. However, it is important to note that nearly 50% of the species in this group are with uncertain trend category. Stable are 14% of them including species like Great Tit, Golden Oriole, Jay and Common Chaffinch. Two species are in decline – Blackbird and Green Woodpecker and only the Chiffchaff increases.

Table. 3 Trends of forest birds

			Total for Bulgaria
	Species name	Scientific name	Change (%)	Sample plots	Trend category
1	European Robin	Erithacus rubecula	12,26	54	?
2	Common Wood Pigeon	Columba palumbus	-25,61	47	?
3	Great Spotted Woodpecker	Dendrocopos major	13,11	86	?
4	Song Thrush	Turdus philomelos	64,43	66	?
5	Blackcap	Sylvia atricapilla	2,13	78	?
6	Northern Chiffchaff	Phylloscopus collybita	77,64	49	↑
7	Great Tit	Parus major	-7,61	110	-
8	Eurasian Nuthatch	Sitta europaea	-35,67	33	?
9	Eurasian Golden Oriole	Oriolus oriolus	-22,78	118	-
10	Eurasian Jay	Garrulus glandarius	1,41	109	-
11	Common Chaffinch	Fringilla coelebs	-44,36	91	-
12	Hawfinch	Coccothraustes coccothraustes	23,81	53	?
13	European Green Woodpecker	Picus viridis	-38,51	58	↓
14	Common Blackbird	Turdus merula	-35,01	123	↓

The data analysis suggests that species with stable trends are generalists in their habitat requirements which brings again the argument for the specific focus of the monitoring scheme on comon forest birds. The population trend of the Blackbird continues to decline from the previous assessment when it was -22% with uncertain trend, now the trend is classified as moderately declining and drops to -35%. Another species in decline is the green woodpecker. It is important to note that the monitoring scheme is not well specialized in capturing population trends of woodpeckers because they breed earlier than other species. Since woodpeckers’ activity is reduced when the CBM is implemented, the lowest registration of the species may be a result of their reduced activity. If the negative trend continues in the years to come, then it may respond to real population changes.

The low coverage of forest habitat in CBM does not allow proper interpretation of results. It is important to note that although the species in this group live in forest, most of them are generalists to some extent. This suggests that they may occur in a variety of habitats including individual trees or small groups of trees with suitable conditions for breeding. On the other hand species like Golden Oriole and Song Thrush are specialized in their habitat preferences and can give more precise image on the state of the habitat. It is necessary to conduct additional specific studies to better understand the reasons for population trends. It is important to not only increase the habitat coverage in CBM but also consider the habitat requirements of species included in the forest bird index.

 

Birds of “other” types of habitat

Species that use more than one type of habitat without being closely related to it are separated into a third category “other”. Species from this group are called generalists. This group also contains species related to urban environment.

Table. 4 Population trends of birds from "other" habitats

			Total for Bulgaria
	Species name	Scienfitic name	Change (%)	Sample plots	Trend
1	Common Swift	Apus apus	25,36	83	?
2	Common Buzzard	Buteo buteo	-35,77	120	?
3	European Greenfinch	Carduelis chloris	-29,46	88	?
4	Hooded Crow	Corvus corone	-60,59	94	↓↓
5	Western Jackdaw	Corvus monedula	-56,92	50	↓
6	Common Cuckoo	Cuculus canorus	-22,27	144	↓
7	Common House Martin	Delichon urbica	-47,21	106	↓
8	Syrian Woodpecker	Dendrocopos syriacus	-52,31	56	↓↓
9	Yellowhammer	Emberiza citrinella	-7,46	46	?
10	Red-rumped Swallow	Hirundo daurica	27,35	38	?
11	Wood Lark	Lullula arborea	171,3	32	↑
12	Common Nightingale	Luscinia megarhynchos	23,03	128	?
13	White Wagtail	Motacilla alba	-23,05	53	?
14	House Sparrow	Passer domesticus	-50,25	111	↓↓
15	Black Redstart	Phoenicurus ochruros	-65,44	24	?
16	Common Magpie	Pica pica	-15,58	131	-
17	Collared Dove	Streptopelia decaocto	-11,76	78	?

 

Results show that Hooded Crow and House Sparrow are again amongst the species with the most unfavourable status in this group. Other species with significant decline is Syrian Woodpecker. Its negative trend is rather alarming because it is a typical representative of parks and gardens in urban areas that represent significant proportion of its habitat. The loss of green areas because of urbanization is a potential reason for the species decline.

Species like Hooded Crow, Magpie and even Rook show significant affiliation to urban environment or increase their presence in this type of habitat in the last years. That is why it is necessary to conduct specific studies for the main reasons for the declines to understand whether the CBM coverage has an impact or specific ecological changes occur and affect other species and the environment in general. Many of these species live in settlements and neighbouring areas. Alarming are the negative trends of Common Cuckoo, House Martin and House Sparrow – widespread species with different habitat preferences.

The only species with stable trend is the Magpie a result of its adaptive behavior. The species with positive trend is woodlark. It occupies open areas in late stage of succession and open oak woodland. Perhaps land abandonment is a factor that influences the species’ population trend. The significant number of the increase is probably a result of the small sample size which is only 32 plots.