Bird Diversity Changes in Tervasaari, Savonranta, Finland from 1989 to 2023

Abstract

Birds are sensitive to climate and environmental changes and monitoring the abundance and distribution of bird populations can be excellent barometers of the health of the environment. To investigate bird diversity changes, a hobby like birding was done from May 1989 until July 2023 on a forested island, at Lake Orivesi in Eastern Finland. The main observation area was some 1 km to all directions from the house mainly used for summer holidays. A total of 145 bird species were identified during the 34 years, 108 during the first period 1989–2000, 102 during the second 2001–2013 and 114 during the third period 2014–2023. Abundance classification listed 48% of species as common, 20% as rare and 32% as occasional. The population trend for 80% of bird species seen more than once or one year in 17% of species have upward trend, in 16% of species trend is downwards and the remaining 67% of species are not showing any clear changes. Bird feeding attracted 28% of species mainly during the winter but later also almost all year around. Interesting behaviour changes have been noted at individual and species levels during the feeding activity and in the use of the nest boxes.

1. Introduction

Distribution ranges of bird species around the globe are expected to contract in response to climate change. The first study addressing the potential consequences of climate change on the biology of birds dates back 32 years [1]. Since then we have gained tremendous knowledge in this field, and every week provides large amounts of information through a steady stream of new publications [2, 3]. A lot of attention has been paid to possible climate change impacts on bird diversity but often with very short observation periods or only covering part of the species [4, 5].

One can read extremely alarming news about the state of the World’s birds according to which one in eight bird species is threatened with extinction [6]. Similar news from Europe indicates that whilst 47% of 463 bird species in the European Union (EU) are in good conservation status, 39% are in poor and bad conservation status [7]. The fact that 14% of all EU bird species have an unknown status highlights the need for this type of study [8].

We have done hobby-like birding on a forested island, at Lake Orivesi in Eastern Finland from May 1989 until July 2023. This long-term data set makes it possible to explore the bird diversity changes in that fairly remote area. The main observation area was some 1 km to all directions from the house mainly used for summer holidays. This paper gives also several particular behaviours of different bird species, especially those attending our bird feeding activities or using the offered nest boxes.

2. Material and methods

Since 1989, we have had a forest house in Tervasaari, Savonranta, 65 km south of Joensuu and 70 km north of Savonlinna. Tervasaari is a small island at Lake Orivesi in East Finland connected with a narrow road to the mainland. Over the years, we have marked down most birds we have seen in the area, which is some 1 km to all directions from the house. Our land includes 600 m of lakeshore and some 3 ha of forest. First years we spent only the summer holidays in that area while working abroad and now after 2007 also winter-time birding has been possible. This however did not affect much in the total bird numbers, as most of the species are migratory.

Tervasaari has been occupied by humans at least for well over 300 years but now only two houses are occupied a year around and two other houses are for summer use only. Until 1900, slash-and-burn method was used in farming and tree burning for tar gave even the name for the place (Tervasaari = tar island). Also later the forest cover has been harvested to some extent but we have avoided falling any large trees from our area. Even the firewood is purchased from outside the area. Small trees were harvested more when we had sheep during one summer. Neighbours are using their forests more effectively (see Figure 1), making our forest a haven for some forest species, like owls (Strigidae) (Figure 2–4) and woodpeckers (Picidae) (Figure 5–7) etc. Figures 8–15 are illustrating some typical and rare Tervasaari birds.

Figure 1.

Unfortunate forest harvesting of the neighbours. Photograph by Heimo Mikkola, Finland.

Figure 2.

Northern Hawk Owl Surnia ulula. Photograph by Esko Rajala, Finland.

Figure 3.

Great Grey Owl Strix nebulosa. Photograph by Esko Rajala, Finland.

Figure 4.

Pygmy Owl Glaucidium passerinum. Photograph by Esko Rajala, Finland.

Figure 5.

Black Woodpecker Dryocopus martius. Photograph by Esko Rajala, Finland.

Figure 6.

White-backed Woodpecker Dendrocopos leucotos. Photograph by Ari Rantamäki, Finland.

Figure 7.

Great Spotted Woodpecker Dendrocopos major. Photograph by Esko Rajala, Finland.

Figure 8.

Whooper Swan Cygnus cygnus. Photograph by Esko Rajala, Finland.

Figure 9.

Barnacle Goose Branta leucopsis. Photograph by Esko Rajala, Finland.

Figure 10.

Sparrowhawk Accipiter nisus. Photograph by Esko Rajala, Finland.

Figure 11.

Common Crane Grus grus. Photograph by Esko Rajala, Finland.

Figure 12.

Waxwing Bombycilla garrulus. Photograph by Esko Rajala, Finland.

Figure 13.

Red-flanked Bluetail Tarsiger cyanurus. Photograph by Jari Peltomäki, Finland.

Figure 14.

Great Grey Shrike Lanius excubitor. Photograph by Esko Rajala, Finland.

Figure 15.

Pine Grosbeak Pinicola enucleator. Photograph by Esko Rajala, Finland.

To reduce the possible inconsistencies in writing down every year’s observations from most common birds, a standard number of years for each period was taken from Chaffinch Fringilla coelebs, which is the most common bird species in Finland [9]. Against that value, the occurrence index was calculated for each other recorded species. Criterias used in abundance and population trend estimations were as follows: C = Common (7 or more observation years); R = Rare (4–6 observation years) and O = Occasional (1–3 observation years); U = upwards (at least 0.4 up), D = downwards (at least 0.4 down) and N = no major trend up or down (less than 0.4 up or down), N/A = seen only once or during one year, so no population trend estimation possible (Table 1).

Number	Species	1989–2000	2001–2013	2014–2023	Status/Abundance	Trend
1	Gavia arctica	0	0.4	0.8	C	U
2	Podiceps cristatus	0.5	0	0.2	R	D
3	Podiceps griseigena	0.5	0.9	0.8	C	U
4	Botaurus stellaris	0.4	0.7	0.7	C	N
5	Ardea cinerea	0	0	0.1	O	N/A
6	Cygnus cygnus	0.1	1.0	1.0	C	U
	Arctic geese unidentified	0	0.4	0.9	C	U
7	Anser fabalis	0	0.1	0.4	R	U
8	Anser brachyrhynchus	0	0	0.2	O	N
9	Anser albifrons	0	0.1	0.2	O	N
10	Anser erythropus	0	0	0.4	R	U
11	Branta canadensis	0	0.1	0.1	O	N
12	Branta leucopsis	0	0	0.7	R	U
13	Branta bernicla	0	0	0.4	R	U
14	Anas penelope	0.4	0.4	0.8	C	U
15	Anas crecca	0.4	0.2	0.3	C	N
16	Anas platyrhynchos	0.4	0.1	0.3	C	N
17	Anas querquedula	0.1	0	0	O	N/A
18	Anas clypeata	0.3	0	0	O	N
19	Clangula hyemalis	0	0	0.2	O	N
20	Melanitta fusca	0	0.1	0.1	O	N
21	Bucephala clangula	1.1	0.7	0.7	C	D
22	Mergus serrator	1.0	0.4	0.5	C	D
23	Mergus merganser	0.4	0.3	0.7	C	N
24	Pernis apivorus	0.3	0.1	0.2	R	N
25	Accipiter gentilis	0.1	0	0.1	O	N
26	Accipiter nisus*	0.3	0.7	0.8	C	U
27	Buteo buteo	0.3	0	0.4	R	N
28	Aquila clanga	0.1	0	0.2	O	N
29	Pandion haliaetus	0.4	0.2	0.4	C	N
30	Falco tinnunculus	1.3	0.2	0.1	C	D
31	Falco columbarius	0.1	0	0.1	O	N
32	Falco subbuteo	0.6	0.2	0.3	C	D
33	Falco peregrinus	0.3	0	0.2	R	N
34	Tetrastes bonasia	0.1	0.3	0.5	C	U
35	Lagopus lagopus	0	0.1	0	O	N/A
36	Tetrao tetrix	1.1	0.3	0.4	C	D
37	Tetrao urogallus	0.3	0.2	0.4	C	N
38	Phasianus colchicus	0.1	0	0	O	N/A
39	Porzana porzana	0.1	0	0	O	N/A
40	Fulica atra	0.1	0	0	O	N/A
41	Grus grus	1.1	0.8	0.9	C	N
42	Vanellus vanellus	0.4	0.2	0.2	R	N
43	Lymnocryptes minimus	0.1	0	0	O	N/A
44	Gallinago gallinago	0.8	0.2	0	C	D
45	Gallinago media	0.1	0.1	0.1	R	N
46	Scolopax rusticola	0.8	0.2	0.8	C	N
47	Limosa lapponica	0	0.1	0	O	N/A
48	Numenius arquata	0.6	0.8	0.4	C	N
49	Tringa nebularis	0.3	0.2	0.1	R	N
50	Tringa ochropus	0	0.2	0.2	R	N
51	Tringa glareola	0	0	0.1	O	N/A
52	Actitis hypoleucos	0.5	0.7	0.5	C	N
53	Hydrocoloeus minutus	0.3	0	0.1	R	N
54	Larus ridibundus	0.6	0.4	0.2	C	D
55	Larus canus*	0.9	1.0	1.0	C	N
56	Larus fuscus	0.1	0.3	0.2	R	N
57	Larus argentatus*	0.4	0.7	0.5	C	N
58	Rissa tridactyla	0	0	0.1	O	N/A
59	Sterna hirundo	0.5	0.3	0.8	C	N
60	Sterna paradisaea	0.1	0	0	O	N/A
61	Chlidonias niger	0	0	0.2	O	N
62	Columba oenas	0	0	0.1	O	N/A
63	Columba palumbus*	0.4	0.3	0.7	C	N
64	Cuculus canorus	0.8	0.7	0.8	C	N
65	Bubo bubo	0	0.2	0.1	R	N
66	Surnia ulula	0	0	0.1	O	N/A
67	Claucidium passerinum*	0.1	0.3	0.3	C	N
68	Strix uralensis*	0.3	0.4	0.2	C	N
69	Strix nebulosa	0.1	0.2	0	R	N
70	Asio otus	0	0.1	0	O	N/A
71	Aegolius funereus	0	0.1	0.1	O	N
72	Jynx torquilla	0.1	0	0	O	N/A
73	Picus canus*	0	0.2	0.8	C	U
74	Dryocopus martius*	0.4	0.4	0.9	C	U
75	Dendrocopos major*	1.3	0.9	1.0	C	N
76	Dendrocopos leucotos*	0.3	0	0.5	R	N
77	Dendrocopos minor*	0.1	0.6	0.2	C	N
78	Picoides tridactylus	0.1	0.1	0	O	N
79	Hirundo rustica	0.4	0.1	0.2	R	N
80	Delichon urbica	0.1	0	0.1	O	N
81	Anthus trivialis	0.6	0.6	0.2	C	D
82	Motacilla alba	1.3	1.0	0.6	C	D
83	Bombycilla garrulus*	0	0.2	0.5	C	U
84	Prunella modularis*	0.3	0.2	0.1	R	N
85	Erithacus rubecula*	1.0	0.3	0.6	C	D
86	Luscinia luscinia	0.3	0	0.1	R	N
87	Tarsiger cyanurus	0	0.1	0	O	N/A
88	Phoenicurus ochruros	0.1	0	0	O	N/A
89	Phoenicurus phoenicurus	0.5	0.2	0.1	C	D
90	Saxicola rubetra	0.1	0	0	O	N/A
91	Zoothera dauma	0	0.1	0	O	N/A
92	Turdus merula*	0.6	0.9	1.0	C	U
93	Turdus pilaris*	1.0	0.7	0.8	C	N
94	Turdus philomelos	0.8	0.6	0.6	C	N
95	Turdus iliacus	0.6	0.9	0.6	C	N
96	Turdus viscivorus	0.1	0.1	0.1	R	N
97	Accrocephalus schoenobaenus	0.6	0	0.2	R	D
98	Acrocephalus dumetorum	0.1	0.1	0	O	N
99	Hippolais icterina	0.3	0.3	0	R	N
100	Sylvia curruca	0.4	0.4	0.2	C	N
101	Sylvia communis	0.1	0	0	O	N/A
102	Sylvia borin	0.8	0.6	0.4	C	D
103	Phylloscopus trochiloides	0.4	0.2	0	R	D
104	Phylloscopus sibilatrix	0.5	0.7	0.7	C	N
105	Phylloscopus collybita	0.1	0.1	0.3	R	N
106	Phylloscopus trochilus	1.0	0.6	0.7	C	N
107	Regulus regulus	0	0.2	0	O	N
108	Muscicapa striata	0.4	0.8	0.4	C	N
109	Ficedula parva	0	0	0.1	O	N/A
110	Ficedula hypoleuca	1.1	1.0	0.9	C	N
111	Panurus biarmicus	0.1	0	0	O	N/A
112	Aegithalos caudatus*	0	0.3	0.2	R	N
113	Poecile palustris*	0	0.2	0.1	O	N
114	Poecile montanus*	0.9	0.9	1.0	C	N
115	Poecile cinctus	0.1	0	0	O	N/A
116	Lophophanes cristatus*	0.4	0.4	0.4	C	N
117	Periparus ater*	0.4	0.4	0.8	C	U
118	Cyanistes caeruleus*	1.0	0.9	1.0	C	N
119	Cyanistes cyanus	0	0.1	0	O	N/A
120	Parus major*	0.9	1.2	1.0	C	N
121	Sitta europaea*	0	0.4	0.6	C	U
122	Certhia familiaris*	0.1	0.3	0.4	C	N
123	Oriolus oriolus	0.8	0	0	R	D
124	Lanius collurio	0.1	0	0	O	N/A
125	Lanius excubitor	0	0.1	0.2	O	N
126	Garrulus glandarius*	0.1	0.3	1.0	C	U
127	Pica pica*	0.5	0.6	1.0	C	U
128	Nucifraga caryocatactes	0	0.1	0	O	N/A
129	Corvus cornix*	1.1	1.0	1.0	C	N
130	Corvus corax*	0.6	0.6	0.8	C	N
131	Passer montanus*	0	0	0.1	O	N/A
132	Fringilla coelebs*	1.0	1.0	1.0	C	N
133	Fringilla montifringilla*	0.3	0.3	0.3	C	N
134	Carduelis chloris*	0.1	1.0	1.0	C	U
135	Carduelis spinus*	0.6	0.6	0.9	C	N
136	Carduelis flammea*	0.3	0.4	0.5	C	N
137	Loxia curvirostra*	0.3	0.2	0.3	C	N
138	Loxia pytyopsittacus	0.1	0	0.2	R	N
139	Carpodacus erythrinus	1.4	0.4	0	C	D
140	Pinicola enucleator	0	0	0.1	O	N/A
141	Pyrrhula pyrrhula*	0.8	0.9	1.1	C	N
142	Coccothraustes coccothraustes*	0	0	0.2	R	N
143	Calcarius lapponicus	0.1	0	0	O	N/A
144	Plectrophenax nivalis	0	0.1	0.1	O	N
145	Emberiza citrinella*	0.3	0.6	0.1	C	D
	Totals	108	102	114	69C; 29R; 47O	20 U; 18D; 78 N; 29 N/A

Table 1.

Relative abundance of all bird species seen in Tervasaari, Savonranta, Finland from May 1989 to June 2023.

^*

Species are seen to visit the bird feeding sites.

Observations presented in three periods and recorded years of each species are divided with the same period years of Chaffinch Fringilla coelebs, Finland’s most common bird species [9]. C = Common (7 or more observation years); R = Rare (4–6 observation years) and O = Occasional (1–3 observation years); U = upwards (at least 0.4 up), D = downwards (at least 0.4 down) and N = no major trend up or down (less than 0.4 up or down), N/A = seen only once or during one year, so no population trend estimation possible.

Bird feeding was undertaken in all years after 2005. The main food served were groundnuts, sunflower seeds, lard and one kg Tintin fat seed bars (60% of animal fat plus oat, soy, vegetable oil and sunflower seeds). In addition, household food remains were given mainly to the larger birds like crows (Corvidae) and gulls (Laridae). Every year, new nest boxes, of different sizes and shapes, have been built so that the final number of nest boxes is well over 50.

3. Results

Richness and relative abundance of all recorded bird species were studied from May 1989 until July 2023. The observations were grouped into three parts, the first part from 1989 to 2000, the second from 2001 to 2013 and the third from 2014 to 2023 (Table 1). A total of 145 bird species were identified over the years, 108 during the first period, 102 during the second and 114 during the third period. Abundance classification listed 69 (48%) species as common, 29 (20%) rare and 47 (32%) as occasional. The population trend was possible to identify only in species seen more than once and in more than one year. Of total species, 116 (80%) were such and in 20 (17%) species trend is going upwards, in 18 (16%) species trend is downwards and the remaining 78 (67%) species are not showing any clear changes. Bird feeding attracted 40 (28%) of species mainly during the winter but later also almost all year around as shown below.

4. Comments on some species

4.1 Black-throated Diver Gavia arctica

Black-throated Diver has been going upwards in Tervasaari waters same time when Great Crested Grebe Podiceps cristatus has gone down although not known if any linkage between these two changes exists.

4.2 Arctic geese

We did not see Arctic geese migration in the early years as we were using the house mainly during the summer. It is also, however, obvious that the amount of Arctic geese, especially the Barnacle Goose Branta leucopsis has had a heavy population increase in all of its northern distribution areas [10]. Winter survival of Barnacle Geese has increased enormously because of their access to higher-quality food in agricultural areas [11]. There are also indications that the migration route of the Arctic geese has moved more towards the west bringing the geese just over Tervasaari [12].

4.3 Birds of Prey and Owls

Predation is often density-dependent, and a higher population density of prey may feedback on the density of predator populations [2]. This was seen clearly in the numbers of Sparrow Hawk Accipiter nisus, Ural Owl Strix uralensis and Pygmy Owl Glaucidium passerinum, which have learned to visit our bird feeding sites. When Sparrow Hawk comes visible, all birds feeding in the area will ‘freeze’ to death, not moving even their eyes. The Red Squirrel Sciurus vulgaris regularly visits the feeding place and also is freezing when noting the hawk. Magpie Pica pica is the largest prey Sparrow Hawk that has been taken, so Squirrel has all reasons to be afraid. Pygmy and Ural Owl may come near the feeding places as there are many voles under the feeders but at least the first one takes readily also small Passerines forming a very important part (up to 40%) of its diet [13].

4.4 Mammal visitors

Feeding place food may bring many mammal predators to the site. Eurasian lynx Lynx lynx, Red fox Vulpes vulpes and Pine Marten Martes martes have learned to steal our fat seed bars and lard, especially if we are not present in the house. Also, Eurasian ermine Mustela erminae has been seen climbing the tree stump to reach the lard at a height of two meters. Raccoon Dog Nyctereutes procyonoides visit the feeding sites but get only some fallen sunflower seeds. Footprints of Wolverine Gulo gulo and Brown Bear Ursus arctos have been seen in our yard but not near the bird feeding tables. Sometimes Roe Deer Capriolus capriolus and White-tailed Deer Odocoileus virginianus may also feed some sunflower seeds on the ground.

4.5 Bullying

Some species, like Greenfinch Carduelis chloris, are born to be bullies towards all smaller species and often even towards the bigger ones, for example, against Bullfinch Pyrrhula pyrrhula, which are less aggressive. However, Greenfinch did not dare to disturb the feeding of Hawfinch Coccothraustes coccothraustes although harassing same time the Bulffinch. Hawfinch was not minding the presence of other birds on the feeding table. Siskin Carduelis spinus was often seen feeding side by side with Hawfinch despite its huge bill and bull neck. Great Tit Parus major, especially male birds are often bullying the smaller tits, like Eurasian Blue Tits Cyanistes caeruleus. When food is plenty, fighting for it is less intense – even bullying.

The Red Squirrel or Jay Garrulus glandarius often keep the feeding table occupied to those other birds or other Squirrels may not enter to feed themselves. However, agile Siskins and Willow Tits Poecile montanus often pick seeds despite the presence of large feeders.

4.6 Learning

Many species like Waxwings Bombucilla garrulus and Redpolls Acanthis flammea have learned to visit below the feeding table to eat the sunflower seeds, which woodpeckers and jays were dropping down. Robin Erithacus rubecula did that same but soon learned to go up to the feeding table. Some Blackbirds Turdus merula learned obviously by observing the woodpeckers how to eat directly fat seed bars, although their legs are not so good for hanging from the net protecting the bar. In addition, Siskins and Long-tailed Tits Aegithalos caudatus have been feeding on the fat seed bars without any problems.

4.7 Mutualism

Clear mutualism is when tits and blackbirds are waiting on the ground below the fat seed bars that woodpeckers will drop small parts for them as well.

4.8 Fight for the nest boxes

Great Tit and Eurasian Blue Tit are reducing the nest box competition by reserving their favourite boxes early in the winter. The problem comes later when the Pied Flycatcher Ficedula hypoleuca is returning from migration because it is a real fighter for the nest boxes. Male birds try to steal the box, especially from Eurasian Blue Tits. On 11/05/2021, three female Pied Flycatchers and one male kept the Eurasian Blue Tit female inside the nest box by force so that the male Blue Tit was not able to feed the incubating female. Later the Pied Flycatcher overtook that nestbox. When cleaning the boxes, there have been cases of the Pied Flycatcher having built its nest over the body of the Blue Tit. The Great Tit is stronger to defend its nesting and can sometimes even harm the Pied Flycatcher.

4.9 Fight for the twig nests

Eurasian Hobby Falco subbuteo was seen fighting with the Hooded Crow for a twig nest on 25/05/2017. Breeding of the Hooded Crow should have been over, so not known if it was just defending the same year-used nest.

4.10 Common Gull Larus canus

On 16/07/2020, when feeding the fish from our pier with breadcrumbs, three Common Gulls came to watch us (or rather small fish!). One Common Gull was much tamer than the others were and was less than 10 m from us. From the game camera photos, it was noted that one Common Gull was also visiting the feeding table.

4.11 Herring Gull Larus argentatus

One big-headed Herring Gull learned to visit the feeding table especially if some Rainbow Trout Oncorhynchus mykiss remains were available. The same Herring Gull was often following us during the fish feeding but not so close as the Common Gull above.

4.12 Wood Pigeon Columba palumbus

Wood Pigeons have also realised that below the bird feeding table, they get easy food. Two birds very often visited the site together but mostly eat only on the ground. At least one of them has learnt to get seeds also from the feeding table.

4.13 Grey-headed Woodpecker Picus canus

This large woodpecker is often very peaceful with other birds sharing the fat seed bars with tits without any problems. However, sometimes male Grey-headed Woodpeckers did not want to share the food with White-backed Woodpecker Dendrocopos leucotos male—both spreading their wings to drive the other away.

4.14 Great spotted Woodpecker Dendrocopos major

This species is a nuisance for smaller birds breeding in the nest boxes by breaking through the walls to reach the young ones. It has been noted that if feeding birds also during the early summer then the Woodpecker damages are much less. They bring their own young ones to feed the seeds in the feeding place instead of breaking the nest boxes. It seems always to be the male, which brings the young Woodpeckers to learn to eat sunflower seeds. First, the father opens the seeds for the young ones until they learn to do it themselves. The seed is placed into a small wood hole, which holds it tight until the hardcover is removed.

One fat female Great Spotted Woodpecker decided that she is the only bird who can eat sunflower seeds from our feeder. She attacked all other species from the size of Siskin to the size of Hooded Crow.

4.15 White-backed Woodpecker

Aggressive behaviour was noted between the male White-backed Woodpecker and the female Great Spotted Woodpecker very often. On 26/03/2016, three White-backed Woodpeckers tried to stop one Great Spotted Woodpecker to enter the feeding table.

4.16 Jay

Normally there were four up to seven Jays in the feeding but on 22/04/2019 there were 15 Jays in our front yard, obviously indicating some kind of return migration from their wintering area if not just presenting several families, which have been nesting nearby. On 16/04/2022, there were 5 + 5 (two families with the young ones) Jays fighting like cats and dogs, which family should be able to feed themselves. After a while, another family gave up and only one of the five groups remained in the feeding.

4.17 Magpie Pica pica

Feeding visits often occurred only very early in the morning and normally alone or not more than two together. One time, end of July 2019, ten Magpies were on the feeding site, which may again is a sign of some invasion. Magpies are learning to spy on the Jays when they are hiding the food from the feeding place. Not known how often Jays are returning in vain to these food caches, which Magpies have stolen.

4.18 Hooded Crow

In Tervasaari, Hooded Crow is a partial migrant and leaves the area during the winter. Autumn departure timing is not so easy to note but happens usually between the end of September and early November. After returning, the birds usually come to announce their presence, so the timing was also easier to record. Over the years, Hooded Crow returned to Tervasaari between 28 February and 29 March as shown inTable 2.

Year	2006	2008	2009	2010	2011	2012	2013	2015	2016	2017	2018	2019	2020	2021	2022	2023
Arrival	12/3	10/3	16/3	18/3	27/3	11/3	19/3	28/2	10/3	22/4	29/3	18/3	09/3	19/3	16/3	17/3

Table 2.

Spring time arrival of the Hooded Crows Corvus corone cornix on the Tervasaari from 2006 to 2023.

In 2014, we arrived from the UK too late in the spring to record the first arrival; also in 2017, the recorded time is far too late to present the first arrival. In folklore, we have a saying that the crows are returning on 24/2 [14] indicating that springtime starts now later than before 1950 despite the overall climate warming.

4.19 Raven Corvus corax

Ravens hold territory during the entire year near their nesting locality and will occasionally go for a ‘winter feeding trip’, for example, in rubbish dumps. Therefore, it is possible that the closing of rubbish dumps influences the winter distribution of the Ravens [15]. In old times, we had a wooden closure without cover for the household food waste. Then the Ravens brought even the young ones to feed next to the house, now the waste is in a closed composter and Ravens are not so regular visitors anymore. The nesting site was also affected by forest harvesting.

4.20 Eurasian Blue Tit

In 2017, Great Spotted Woodpecker ate the Eurasian Blue Tit young ones from a nest box in May. In early June, the same pair started a new nest in another nest box, some 50 m from the first box. Again, the Great Spotted Woodpecker broke the box wall and ate the young ones despite the plywood strengthening the wall of that box. The third time that pair nested in a third box behind our sauna, and finally succeeded. The young ones left that nest box on 24/07/2017 without any disturbance from the Great Spotted Woodpecker. Unfortunately, summer feeding started only regularly after 2017 as that stopped almost completely these Great Spotted Woodpecker attacks on smaller bird nest boxes.

4.21 Chaffinch

During the spring migration, there has been some 50 Chaffinch in front of the house but only three or four of those will dare to enter the feeding table. Those pairs that remain in the site for breeding are later more regular in the feeding and will also encourage the later returning Bramblings Fringilla montifringilla to enter the feeding table.

4.22 Summer feeding

If feeding was continued until the end of June, many species, like Bullfinch, Chaffinch, Great Tit, Greenfinch, Hooded Crow, Siskins and earlier mentioned Great Spotted Woodpecker, bring their young ones to the feeding table. It is almost always the male first feeding the young ones while teaching them how to eat sunflower seeds and groundnuts. Interestingly, Eurasian Blue Tit does not bring the young ones but visits the feeder and takes food to the young ones waiting nearby. Later well-flying young ones come to feeding table independently.

4.23 Forest harvesting

Our neighbours started to harvest their forests in 2019 and 2023 less than 100 and 500 meters away from our forest. The disappearance of old spruce forests affected immediately the abundance of such species as Willow Tit, Crested Tit Lophophanes cristatus and maybe also Coal Tit Periparus ater. Next summer will show if these species have disappeared forever as it now started to look during the 2023 winter feeding. Elsewhere in Finland modification, fragmentation and loss of boreal forest are known to have a major role for instance in the decline of the Crested and Willow Tit populations [16, 17].

5. Discussion

In this study, we noted an increase in Black-throated Loon and a decrease in Great Crested Grebe. That same change was noted in a country-wide inland water study [18] in which 10 of the 16 common waterfowl species showed significant declines and only three species (Whooper Swan Cygnus cygnus, Mallard Anas platyrhynchos and already mentioned Black-throated Loon), have increased in 1986–2018.

Our results show a decline in the populations of the Little Gull Hydrocoloeus minutus and Black-headed Gull Larus ridibundus. The overall decrease in waterfowl has been connected to the low number of Black-headed Gulls [18]. While breeding in the large gull colonies, the waterfowl enjoyed good protection against raptor and mammal predation [19].

On the European scale [20], the status of the Common Snipe Gallinago gallinago has changed from least concern to vulnerable primarily due to habitat loss and degradation in its breeding grounds. Our results confirm this after the neighbour was drying the nearby marsh where this bird was breeding. Common Snipe has not been recorded in this study since 2011. Marsh drying was destroying also the breeding place of Little Gulls and Black-headed Gulls.

A different story is the Great Spotted Woodpecker, which on a European scale [20] has a declining population due to unsustainable forestry practices but in our area is doing very well mainly due to feeding operations. Rapid increases of Grey-headed Woodpeckers and Blue Tits have been noted in this study as well as in the countrywide study [16] and the most likely reason is again the improved food supply due to winter-feeding.

Wintering bird populations can track habitat and climate change better than breeding populations [15]. A typical example is the Eurasian Jay, which has benefitted from global warming since its population range has expanded in Finland [21]. The Eurasian Jay increased in our study period from 0.1 to 1.0 and is also more common and abundant elsewhere in the Finnish winter-feeding sites [22].

6. Conclusions

The range and distribution of bird species worldwide are shifting in response to climate change, which can affect species occupancy either directly by exceeding physiological constraints (e.g., heat tolerance) or indirectly by altering resource availability or other ecological conditions [23]. Since 1980, a loss of 560–620 million individual birds has been reported, that is, 17–19% of the overall breeding bird abundance in the area of the European Union [24, 25]. Based on regional and global alarming reports on climate change, one would have expected much more drastic changes in our study area. A total of 145 bird species were identified during 34 years, which represents 32% of the European breeding species [25]. Only 16% of the 116 regular species have been recorded to go downwards while almost the same amount (17%) of the species have shown an upward trend in their occurrence between 1989 and 2023. Naturally, the small study site is a well-protected area from many anthropogenic impacts, including water and air pollution, urban noise and light disturbance, and the feeding of the birds and numerous nest boxes have assisted their survival and diversity. The future of Tervasaari birdlife does not look as good as two next-door neighbours were harvesting heavily their forests in 2019 and 2023. Remains to be seen how badly the disappearance of the old spruce forest will affect the abundance of birds listed in this study.

Acknowledgments

The authors want to express their best thanks to the Finnish photographers, namely Esko Rajala, Jari Peltomäki and Ari Rantamäki, who kindly forwarded their amazing images for this chapter.