@Entity
@Table(name = "bird")
public abstract class Bird extends BaseEntity {
    @Column(name = "name")
    private String name;

    @Enumerated
    private BirdSize size;

    @Column(name = "photo_url")
    private String photoURL;

    @ElementCollection(targetClass = Color.class, fetch = FetchType.EAGER)
    @CollectionTable(name = "bird_color", joinColumns = @JoinColumn(name = "bird_id"))
    @Column(name = "color")
    @Enumerated
    private List<Color> colors = new ArrayList<>();

    // Constructors and methods removed for brevity
}

@Entity
@Table(name = "natural_reserve")
public class NaturalReserve extends BaseEntity {

    @Column(name = "name")
    private String name;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "region_id")
    private Region region;

    // Just for cascade delete, no getter and setter
    @OneToMany(mappedBy = "reserve", cascade = CascadeType.REMOVE, orphanRemoval = true,
               fetch = FetchType.LAZY)
    private List<Chance> chances = new ArrayList<>();

    // Constructors and methods removed for brevity
}

@Entity
@Table(name = "chance")
public class Chance extends BaseEntity {

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "bird_id")
    private Bird bird;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "natural_reserve_id")
    private NaturalReserve reserve;

    @Enumerated
    private Month month;

    @Column(name = "probability")
    private Double probability;

    // Constructors and methods removed for brevity
}

@Entity
@Table(name = "region")
public class Region extends BaseEntity {

    @Column(name = "name")
    private String name;

    // Constructors and methods removed for brevity
}