VIRUS and Others (Environment - Conservation of wild birds - Prohibition on deliberately disturbing birds - Judgment) [2026] EUECJ C-131/24 (26 February 2026)

Judgment This request for a preliminary ruling concerns the interpretation of Articles 2 and 5 of Directive 2009/147/EC of the European Parliament and of the Council of 30 November 2009 on the conservation of wild birds (OJ 2010 L 20, p. 7; 'the Birds Directive'). The request has been made in the context of a dispute between Umweltorganisation VIRUS – Verein Projektwerkstatt für Umwelt und Soziales (Project Workshop Association for Environment and Social Affairs; 'VIRUS'), Bürgerinitiative 'Nein zur Spange Wörth' (Citizen's Initiative 'No to the Wörth Bypass'), Umweltorganisation Verein Lebenswertes Traisental (Association for a Livable Traisen Valley), Umweltorganisation FG LANIUS – Forschungsgemeinschaft für regionale Faunistik und angewandten Naturschutz (FG LANIUS – Research Community for Regional Faunistics and Applied Nature Conservation) and A. H. and Others, on the one side, and Land Niederösterreich, represented by the Amt der Niederösterreichischen Landesregierung, Abteilung Landesstraßenplanung – ST3 (Office of the Government of the Land of Lower Austria, service 'Planning of roads falling within the competence of the Land' – ST3), on the other side, concerning the decision to authorise the construction of a national road. Legal context European Union law The Birds Directive Recitals 3, 5, 7 and 8 of that directive state: '(3) A large number of species of wild birds naturally occurring in the European territory of the Member States are declining in number, very rapidly in some cases. This decline represents a serious threat to the conservation of the natural environment, particularly because of the biological balances threatened thereby. … (5) The conservation of the species of wild birds naturally occurring in the European territory of the Member States is necessary in order to attain the [European] Community's objectives regarding the improvement of living conditions and sustainable development. … (7) Conservation is aimed at the long-term protection and management of natural resources as an integral part of the heritage of the peoples of Europe. It makes it possible to control natural resources and governs their use on the basis of the measures necessary for the maintenance and adjustment of the natural balances between species as far as is reasonably possible. (8) The preservation, maintenance or restoration of a sufficient diversity and area of habitats is essential to the conservation of all species of birds. Certain species of birds should be the subject of special conservation measures concerning their habitats in order to ensure their survival and reproduction in their area of distribution. Such measures must also take account of migratory species and be coordinated with a view to setting up a coherent whole.' Under Article 1 of the said directive: '1. This Directive relates to the conservation of all species of naturally occurring birds in the wild state in the European territory of the Member States to which the Treaty applies. It covers the protection, management and control of these species and lays down rules for their exploitation. 2. It shall apply to birds, their eggs, nests and habitats.' Article 2 of the same directive provides: 'Member States shall take the requisite measures to maintain the population of the species referred to in Article 1 at a level which corresponds in particular to ecological, scientific and cultural requirements, while taking account of economic and recreational requirements, or to adapt the population of these species to that level.' Article 5 of the Birds Directive provides: 'Without prejudice to Articles 7 and 9, Member States shall take the requisite measures to establish a general system of protection for all species of birds referred to in Article 1, prohibiting in particular: (a) deliberate killing or capture by any method; (b) deliberate destruction of, or damage to, their nests and eggs or removal of their nests; (c) taking their eggs in the wild and keeping these eggs even if empty; (d) deliberate disturbance of these birds particularly during the period of breeding and rearing, in so far as disturbance would be significant having regard to the objectives of this Directive; (e) keeping birds of species the hunting and capture of which is prohibited.' Under Article 9 of that directive: '1. Member States may derogate from the provisions of Articles 5 to 8, where there is no other satisfactory solution, for the following reasons: (a) – in the interests of public health and safety, – in the interests of air safety, – to prevent serious damage to crops, livestock, forests, fisheries and water, – for the protection of flora and fauna; (b) for the purposes of research and teaching, of re-population, of re-introduction and for the breeding necessary for these purposes; (c) to permit, under strictly supervised conditions and on a selective basis, the capture, keeping or other judicious use of certain birds in small numbers.' The Habitats Directive Article 2 of Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora (OJ 1992 L 206, p. 7; 'the Habitats Directive') provides: '1. The aim of this Directive shall be to contribute towards ensuring bio-diversity through the conservation of natural habitats and of wild fauna and flora in the European territory of the Member States to which the Treaty applies. 2. Measures taken pursuant to this Directive shall be designed to maintain or restore, at favourable conservation status, natural habitats and species of wild fauna and flora of Community interest. 3. Measures taken pursuant to this Directive shall take account of economic, social and cultural requirements and regional and local characteristics.' Article 6 of that directive provides: '1. For special areas of conservation, Member States shall establish the necessary conservation measures involving, if need be, appropriate management plans specifically designed for the sites or integrated into other development plans, and appropriate statutory, administrative or contractual measures which correspond to the ecological requirements of the natural habitat types in Annex I and the species in Annex II present on the sites. 2. Member States shall take appropriate steps to avoid, in the special areas of conservation, the deterioration of natural habitats and the habitats of species as well as disturbance of the species for which the areas have been designated, in so far as such disturbance could be significant in relation to the objectives of this Directive. 3. Any plan or project not directly connected with or necessary to the management of the site but likely to have a significant effect thereon, either individually or in combination with other plans or projects, shall be subject to appropriate assessment of its implications for the site in view of the site's conservation objectives. In the light of the conclusions of the assessment of the implications for the site and subject to the provisions of paragraph 4, the competent national authorities shall agree to the plan or project only after having ascertained that it will not adversely affect the integrity of the site concerned and, if appropriate, after having obtained the opinion of the general public. 4. If, in spite of a negative assessment of the implications for the site and in the absence of alternative solutions, a plan or project must nevertheless be carried out for imperative reasons of overriding public interest, including those of a social or economic nature, the Member State shall take all compensatory measures necessary to ensure that the overall coherence of Natura 2000 is protected. It shall inform the Commission of the compensatory measures adopted. Where the site concerned hosts a priority natural habitat type and/or a priority species, the only considerations which may be raised are those relating to human health or public safety, to beneficial consequences of primary importance for the environment or, further to an opinion from the Commission, to other imperative reasons of overriding public interest.' Under Article 12 of the same directive: '1. Member States shall take the requisite measures to establish a system of strict protection for the animal species listed in Annex IV (a) in their natural range, prohibiting: (a) all forms of deliberate capture or killing of specimens of these species in the wild; (b) deliberate disturbance of these species, particularly during the period of breeding, rearing, hibernation and migration; (c) deliberate destruction or taking of eggs from the wild; (d) deterioration or destruction of breeding sites or resting places. 2. For these species, Member States shall prohibit the keeping, transport and sale or exchange, and offering for sale or exchange, of specimens taken from the wild, except for those taken legally before this Directive is implemented. 3. The prohibition referred to in paragraph 1 (a) and (b) and paragraph 2 shall apply to all stages of life of the animals to which this Article applies. 4. Member States shall establish a system to monitor the incidential capture and killing of the animal species listed in Annex IV (a). In the light of the information gathered, Member States shall take further research or conservation measures as required to ensure that incidental capture and killing does not have a significant negative impact on the species concerned.' Austrian law Paragraph 18 of the Niederösterreichisches Naturschutzgesetz 2000 (Law of Lower Austria on Nature Protection 2000) (LGBl. 5500-0), entitled 'Protection of species', provides: '1. The rules on protection of species shall serve to protect and maintain species of wild fauna and flora in their natural and historical diversity. Species protection encompasses: (1) the protection of animals, plants and their biocoenoses against harm caused by man, in particular by their being taken, (2) the protection, maintenance, development and restoration of habitats of species of wild fauna and flora and the safeguarding of their other conditions of life … 2. The Land Government shall, by regulation, declare as protected species, completely or, where sufficient to conserve the species, partially or temporarily, wild plants or wild animals which are not game within the meaning of the Niederösterreichisches Jagdgesetz 1974 [(Lower Austrian Hunting Law of 1974)] (LGBl. 6500), whose population needs to be protected or maintained: (1) because of their rarity or a threat to their population, (2) for scientific reasons or reasons relating to the region's heritage, (3) because of their use or their importance for the ecosystem, or (4) in order to preserve the diversity or characteristic features of nature and landscape. The regulation may designate the species of fauna and flora whose population in the territory of the Land is threatened with extinction. … 4. In the case of the species specially protected under subparagraphs 2 and 3, it is prohibited: … (3) to damage, destroy or take away eggs, larvae, chrysalises or nests of these animals or their nesting, breeding or spawning sites or places of refuge, and (4) to disturb the biotopes, breeding sites and sites of habitation of the species threatened with extinction and listed in the regulation, in particular by photographing or filming.' The dispute in the main proceedings and the questions referred for a preliminary ruling In 2014, the Land of Lower Austria applied for authorisation to construct, in a partly wooded area to the south of St. Pölten (Austria), a 1.69-kilometre dual carriageway, connecting to the S34 expressway. Following the environmental impact assessment, that project was authorised by a decision of 12 November 2019. The applicants in the main proceedings instituted actions against that decision before the Bundesverwaltungsgericht (Federal Administrative Court, Austria), which is the referring court. They argue before that court that the open-field breeding grounds of the skylark, grey partridge and corncrake, which are ground-nesting birds, are located within the perimeter of the works and that the noise caused by future motor traffic will also disturb many species of forest birds near that perimeter, in particular the middle-spotted woodpecker. The planned road should, according to estimates, carry approximately 12 000 vehicles per day. It is apparent from the request for a preliminary ruling that, in order to limit the impact on wild bird populations present on or near the site, the project at issue provides for various measures, in particular that the works may be carried out only during certain months of the year and that old trees must be kept at a distance of at least 300 metres from the road and over an area of 6.6 hectares. According to the report of the two experts appointed by the referring court, if the planned measures are implemented, they will enable any significant disturbing effects on the species concerned to be avoided. The experts acknowledge, however, that those measures will not prevent individual specimens from being affected by that project, if only because of the lifespan of the majority of the forest birds concerned. They nevertheless assure that those measures will guarantee the safeguarding of the habitat of those species and the conditions required for their nesting. The applicants in the main proceedings dispute that assessment. The referring court asks, in the first place, whether measures intended to prevent or limit disturbances to the bird species concerned by the project at issue may be taken into account in order to assess whether that project satisfies the requirements of Article 5(d) of the Birds Directive. It considers that the Court's case-law prohibiting the taking into account of measures aimed at avoiding or reducing adverse effects on the protected site at the stage of the screening preceding the appropriate assessment provided for in Article 6(3) of the Habitats Directive cannot be transposed to Article 5(d) of the Birds Directive. The referring court considers it necessary, on the contrary, to align the interpretation of Article 5(d) of the Birds Directive with that of Article 12(1)(d) of the Habitats Directive, as formulated by the Commission in its Guidance document on the strict protection of animal species of Community interest under the latter directive [C(2021) 7301 final]. The essential criterion resulting from that interpretation is that the permanent ecological function of the site be maintained or improved. As Article 5(d) of the Birds Directive prohibits only disturbances which are significant having regard to the objectives of that directive, the existence of such significance should be assessed taking into account the measures for preventing and mitigating the disturbances entailed by the project. The implementation of a derogation under Article 9 of the said directive is necessary only if the project, together with those measures, must be prohibited pursuant to Article 5(d) of the same directive. In the second place, the referring court asks what proof of the effectiveness of the measures for preventing or reducing the disturbing effects of the project must be required. More specifically, it seeks to ascertain whether the level of certainty as to the effectiveness of those measures, required by Article 5(d) of the Birds Directive, is comparable to that which, in its Guidance document on the strict protection of animal species of Community interest under the Habitats Directive, the Commission considers to be required by Article 12(1)(d) of the latter directive. The interpretation favoured by the Commission would lead to an assessment of the effectiveness of measures for preventing and mitigating disturbances based on the reports of experts designated by the authorities or the court, provided that the assessments contained therein are scientifically defensible, in the current state of knowledge, and are reasoned in detail. However, the referring court considers that the assessments of court experts presenting those characteristics would not be sufficient if one were to apply the standard of proof defined by the Court in relation to measures for preventing or reducing adverse effects, as referred to in Article 6(3) of the Habitats Directive, according to which any reasonable scientific doubt must be excluded. It questions whether it must apply the standard of proof relating to the implementation of Article 12(1)(d) of the Habitats Directive or that concerning measures for preventing or reducing the adverse effects referred to in Article 6(3) of that directive. It sees no reason not to use the latter criterion when assessing the protection of the animal species concerned by the project at issue. Thus, the effectiveness of those measures must be attested to such an extent by scientific documentation that there remains no reasonable doubt whatsoever on that point. In the case at hand, that would mean that the proposed measures concerning the middle-spotted woodpecker cannot be regarded as capable of ensuring the continuity of that species' biological function, in the absence of scientific documentation attesting to their effectiveness. In those circumstances the Bundesverwaltungsgericht (Federal Administrative Court) decided to stay the proceedings and to refer the following questions to the Court of Justice for a preliminary ruling: '1. Is Article 5 of [the Birds Directive] to be interpreted as meaning that a case of deliberate disturbance, as referred to under point (d) of that article, is not constituted if, notwithstanding the fact that individual specimens of certain species could be disturbed, any effect on the objective of Article 2 of that directive will be prevented by means of measures effectively implemented in a timely and appropriate manner? 2. If the first question is answered in the affirmative, must all scientific doubt concerning the effectiveness of the measures be excluded, as evidenced by a well-reasoned, professional appraisal of a court-appointed expert, or must there be objective scientific literature of successful practical experiences of those measures?' The request for the oral part of the procedure to be reopened By document lodged at the Court Registry on 21 October 2025, VIRUS requested that the oral part of the procedure be reopened, pursuant to Article 83 of the Rules of Procedure of the Court. In support of its request, VIRUS maintains that the Opinion of Advocate General Kokott in Voore Mets and Lemeks Põlva (C‑784/23, EU:C:2025:67 ), the judgment of 1 August 2025, Voore Mets and Lemeks Põlva (C‑784/23, EU:C:2025:609 ) and the Opinion of the Advocate General in the present case were delivered after the close of the written procedure and constitute new facts of such a nature as to be a decisive factor for the decision of the Court. In addition, VIRUS bases its request that the oral procedure be reopened on the basis of its disagreement with that Opinion. By virtue of Article 83 of its Rules of Procedure, the Court may, at any time, after hearing the Advocate General, order the reopening of the oral part of the procedure, in particular if it considers that it lacks sufficient information or where a party has, after the close of that part of the procedure, submitted a new fact which is of such a nature as to be a decisive factor for the decision of the Court. That is not the situation here. After all, neither the Opinion delivered by Advocate General Kokott in Voore Mets and Lemeks Põlva (C‑784/23, EU:C:2025:67 ) or in the present case nor the judgment of 1 August 2025, Voore Mets and Lemeks Põlva (C‑784/23, EU:C:2025:609 ) constitute new facts which are of such a nature as to be a decisive factor for the decision that the Court is called upon to give in the present case. In addition, in the light of all the information available to it, the Court considers that it has sufficient information to rule on the present request for a preliminary ruling. So far as concerns VIRUS's disagreements with the Opinion referred to in paragraph 33 of the present judgment, it must moreover be noted, first, that the Statute of the Court of Justice of the European Union and the Rules of Procedure make no provision for the interested parties referred to in Article 23 of the Statute to submit observations in response to the Advocate General's Opinion (judgment of 16 November 2021, Prokuratura Rejonowa w Mińsku Mazowieckim and Others , C‑748/19 to C‑754/19, EU:C:2021:931 , paragraph 30 and the case-law cited). Second, in accordance with the second paragraph of Article 252 TFEU, the Advocate General is to make, in open court, acting with complete impartiality and independence, reasoned submissions on cases which, in accordance with the Statute of the Court of Justice of the European Union, require the Advocate General's involvement. It is not therefore an opinion addressed to the judges or to the parties which stems from an authority outside the Court, but rather, it is the individual reasoned opinion, expressed in open court, of a Member of the Court of Justice itself. In those circumstances, the Advocate General's Opinion cannot be debated by the parties (see, to that effect, judgment of 6 October 2021, Sumal , C‑882/19, EU:C:2021:800 , paragraph 21). Furthermore, the Court is not bound either by the Advocate General's submissions or by the reasoning which led to those submissions. Consequently, a party's disagreement with the Opinion of the Advocate General, irrespective of the questions that he or she examines in the Opinion, cannot in itself constitute grounds justifying the reopening of the oral procedure (judgment of 16 November 2021, Prokuratura Rejonowa w Mińsku Mazowieckim and Others , C‑748/19 to C‑754/19, EU:C:2021:931 , paragraph 31 and the case-law cited). In those circumstances, the Court considers, after hearing the Advocate General, that there is no need to order the reopening of the oral part of the procedure. Consideration of the questions referred The first question By its first question, the referring court asks, in essence, whether Article 5(d) of the Birds Directive must be interpreted as meaning that there is no deliberate disturbance, within the meaning of that provision, where measures, implemented as part of a project, make it possible to prevent any significant effect having regard to the objectives of that directive. In the first place, it should be recalled, first, that, in accordance with Article 5(d) of the Birds Directive, Member States must prohibit the deliberate disturbance of all species of wild birds naturally occurring in the European territory of the Member States, particularly during the period of breeding and rearing, in so far as any such disturbance would be significant having regard to the objectives of that directive. Second, it should also be recalled that that prohibition supplements other prohibitions laid down in Article 5(a) and (b) of that directive, which relate in particular to the deliberate killing or capture of birds of those species and to the deliberate destruction or damage to their nests and eggs. Those prohibitions, however, apply not only to human activities the purpose of which is to cause harm to birds, but also to those for which the possibility of such harm is accepted even though they do not manifestly have such a purpose (see, to that effect, judgment of 1 August 2025, Voore Mets and Lemeks Põlva , C‑784/23, EU:C:2025:609 , paragraph 49). Consequently, the road construction project at issue in the main proceedings, although not intended to harm birds, may fall within the scope of Article 5(d) of the Birds Directive. Third, it is apparent from Article 1 of the Birds Directive, read in the light of recitals 3, 5, 7 and 8 thereof, that the objectives of that directive are to maintain or restore to a sufficient level the population of all species of naturally occurring birds in the wild state in the European territory of the Member States. By virtue of Article 2 of the Birds Directive, that level must correspond in particular to ecological, scientific and cultural requirements, taking account of economic and recreational requirements (see, to that effect, judgment of 1 August 2025, Voore Mets and Lemeks Põlva , C‑784/23, EU:C:2025:609 , paragraph 51). Thus, Article 5(d) of the Birds Directive prohibits disturbances which have a significant effect on the level deemed sufficient for the populations of wild bird species, and not on specimens of those species, unless the population of a given wild bird species is numerically reduced to such an extent that the disturbance of isolated specimens of that species is such as to jeopardise its conservation. In the second place, in order to interpret Article 5(d) of the Birds Directive for the purposes of answering the first question, it is necessary, according to settled case-law, to have regard not to only its wording but also the context in which it occurs and the objectives pursued by the rules of which it is part (see, to that effect, judgment of 4 March 2021, Föreningen Skydda Skogen , C‑473/19 and C‑474/19, EU:C:2021:166 , paragraph 32 and the case-law cited). First, regarding the wording of Article 5(d) of the Birds Directive, it should be noted that, unlike the prohibitions laid down in Article 5(a) and (b) of that directive, the prohibition set out therein, namely the prohibition of deliberate disturbance of birds, particularly during the period of breeding and rearing, applies 'in so far as disturbance would be significant having regard to the objectives of [that d]irective' (judgment of 1 August 2025, Voore Mets and Lemeks Põlva , C‑784/23, EU:C:2025:609 , paragraph 50). Consequently, unlike what is required for the application of Article 5(a) and (b) of the same directive, the examination of the effect of a human activity on the population level of the bird species concerned is relevant for the purposes of applying the prohibition laid down in Article 5(d) of the Birds Directive (see, to that effect, judgment of 1 August 2025, Voore Mets and Lemeks Põlva , C‑784/23, EU:C:2025:609 , paragraph 54). It follows that, if appropriate preventive measures effectively prevent a project from disturbing wild birds or are effectively capable of reducing that disturbance such that it does not have significant effects on the objectives of the Birds Directive, it follows from the wording of Article 5(d) thereof and from the context of that provision that the prohibition of deliberate disturbance referred to in that provision is not applicable. The existence of such measures, the implementation of which is provided for by the project, must therefore be taken into consideration in assessing whether the prohibition on disturbance of wild birds laid down in Article 5(d) of the Birds Directive precludes the project. Second, it is not necessary, in order to attain the objectives of the Birds Directive, recalled in paragraph 40 of the present judgment, namely the maintenance or restoration to a sufficient level of the population of wild bird species, that the disturbing effects of a project on wild bird species be assessed independently of the accompanying measures proposed for the project to prevent or reduce those effects. After all, the disturbances which will actually be suffered by the wild bird species as a result of the implementation of the project, as accompanied by those measures, are alone relevant in the light of those objectives. That analysis is not contradicted by the solution adopted by the Court in the judgment of 12 April 2018, People Over Wind and Sweetman (C‑323/17, EU:C:2018:244 ), contrary to what the applicants in the main proceedings maintain in their written observations. Although, as the Court held in that judgment, measures intended to avoid or reduce the harmful effects of a project must not be taken into account at the screening stage of that project within the framework of the Habitats Directive, that is because, at that first stage of analysis, it is necessary to determine whether that project must be subject to the formal procedure for assessing its implications for a protection area, in accordance with the first sentence of Article 6(3) of the Habitats Directive. However, since Article 5(d) of the Birds Directive does not distinguish between two stages of assessment of the disturbances that projects are liable to cause to wild bird species, such disturbances must be assessed comprehensively from the outset, taking into account to that end measures intended to prevent or mitigate them. It follows from the foregoing that Article 5(d) of the Birds Directive must be interpreted as meaning that there is no deliberate disturbance, within the meaning of that provision, where measures, implemented as part of a project, make it possible to prevent any significant effect contrary to that directive's objectives of maintaining or restoring to a sufficient level the population of all species of naturally occurring birds in the wild state in the European territory of the Member States, taking into account, in particular, ecological, scientific and cultural requirements, as well as economic and recreational requirements. The second question By its second question, the referring court asks, in essence, whether the effectiveness of measures intended to prevent any disturbance having a significant effect on wild bird species, within the meaning of Article 5(d) of the Birds Directive, may be proved by the reasoned assessment of a court expert or whether it must be established by means of scientific documentation attesting to the successful implementation of such measures. It is appropriate to note, in the first place, as the Advocate General did in point 86 of her Opinion, that neither Article 5 nor any other provision of the Birds Directive provides for rules on the taking of evidence in the context of the examination of disturbance caused to wild bird species by human activity. In that regard, under the principle of procedural autonomy and subject to the principles of equivalency and effectiveness, it is for the national legal order of each Member State to establish the ways in which evidence is to be elicited, what evidence is to be admissible before the appropriate national court, or the principles governing that court's assessment of the probative value of the evidence adduced before it and also the level of proof required (see, to that effect, judgment of 21 June 2017, W and Others , C‑621/15, EU:C:2017:484 , paragraph 25). The principle of equivalence requires that those procedural rules not be less favourable than those governing similar domestic situations (see, to that effect, judgment of 8 May 2025, Beevers Kaas , C‑581/23, EU:C:2025:323 , paragraph 44). Consequently, that principle does not preclude proof of the effectiveness of measures intended to prevent any significant disturbance of the species concerned from being adduced by the reasoned assessment of a court expert, if national law allows that method of proof for similar situations governed by domestic law, which it is for the referring court to ascertain. The principle of effectiveness requires that the said procedural rules do not render practically impossible or excessively difficult the implementation of EU law (see, to that effect, judgments of 21 June 2017, W and Others , C‑621/15, EU:C:2017:484 , paragraph 26 and the case-law cited, and of 30 January 2025, Caronte & Tourist , C‑511/23, EU:C:2025:42 , paragraph 44). In that regard, it is worth noting, as the Advocate General considered, in essence, in point 88 of her Opinion, as regards the prohibition on deliberate disturbance of wild birds laid down in Article 5(d) of the Birds Directive, that the principle of effectiveness requires that it must not be made unreasonably difficult to prove that such a disturbance has significant effects on the objectives of that directive. Such a consideration applies also to proof that the disturbance has no significant effects on the objectives of the said directive. In the second place, it must be borne in mind that the Member States are required, when they implement EU law, to ensure compliance with the requirements of the principle of sound administration (see, to that effect, judgment of 22 September 2022, Országos Idegenrendészeti Főigazgatóság and Others , C‑159/21, EU:C:2022:708 , paragraph 44 and the case-law cited). That principle requires, inter alia, the administrative authorities to conduct a diligent and impartial examination of all the relevant matters so that, when they adopt a decision, they have at their disposal the most complete and reliable information possible (see, to that effect, judgment of 14 May 2020, Agrobet CZ , C‑446/18, EU:C:2020:369 , paragraph 44 and the case-law cited). The principle of sound administration also requires the administration to give reasons for its decision when implementing EU law (see, to that effect, judgment of 24 February 2022, SC Cridar Cons , C‑582/20, EU:C:2022:114 , paragraph 54 and the case-law cited). In the third place, so far as concerns the environmental risk assessment, in accordance with Article 191(2) TFEU, it must be carried out in compliance with the precautionary principle. With that in mind, it is the duty of the competent authorities, in particular, to take account of the most reliable scientific data available and the most recent results of international research (see, to that effect, judgments of 1 October 2019, Blaise and Others , C‑616/17, EU:C:2019:800 , paragraphs 46, 93 and 94, and of 12 June 2025, Eesti Suurkiskjad , C‑629/23, EU:C:2025:429 , paragraph 42). However, proof of the effectiveness of those measures cannot be required in the form of scientific documentation attesting to the successful implementation of those measures, since such documentation will not necessarily be available. In the light of the foregoing observations, the answer to the second question is that the effectiveness of measures intended to prevent any disturbance having a significant effect on wild bird species, within the meaning of Article 5(d) of the Birds Directive, may be proved by the reasoned assessment of a court expert, provided that it is based on the most reliable scientific data available and on the most recent results of international research. However, proof of the effectiveness of those measures cannot be required in the form of scientific documentation attesting to the successful implementation of the said measures. Costs Since these proceedings are, for the parties to the main proceedings, a step in the action pending before the national court, the decision on costs is a matter for that court. Costs incurred in submitting observations to the Court, other than the costs of those parties, are not recoverable. On those grounds, the Court (First Chamber) hereby rules: 1. Article 5(d) of Directive 2009/147/EC of the European Parliament and of the Council of 30 November 2009 on the conservation of wild birds must be interpreted as meaning that there is no deliberate disturbance, within the meaning of that provision, where measures, implemented as part of a project, make it possible to prevent any significant effect contrary to that directive's objectives of maintaining or restoring to a sufficient level the population of all species of naturally occurring birds in the wild state in the European territory of the Member States, taking into account, in particular, ecological, scientific and cultural requirements, as well as economic and recreational requirements. 2. The effectiveness of measures intended to prevent any disturbance having a significant effect on wild bird species, within the meaning of Article 5(d) of Directive 2009/147, may be proved by the reasoned assessment of a court expert, provided that it is based on the most reliable scientific data available and on the most recent results of international research. However, proof of the effectiveness of those measures cannot be required in the form of scientific documentation attesting to the successful implementation of the said measures. [Signatures] * Language of the case: German. © European Union The source of this judgment is the Europa web site. The information on this site is subject to a information found here: Important legal notice . This electronic version is not authentic and is subject to amendment. BAILII: Copyright Policy | Disclaimers | Privacy Policy | Feedback | Donate to BAILII