$birthRepository = new BirthRepository();
$qb = $birthRepository->createQueryBuilder('getDistinctBirths');

$qb->distinct()
    ->select('IDENTITY(b.species)')
    ->from(BirthModel::class, 'b')
    ->where('b.public = :public')
    ->setParameter('public', true);

$entries = $qb->getQuery()->getArrayResult();
trigger_error(print_r($entries, true));

An exception occurred while executing 'SELECT a0_.species_id AS sclr_0 FROM aneBirths a1_, aneBirths a0_ WHERE a0_.bPublic = ?' with params [1]:

Unknown column 'a0_.species_id' in 'field list'

/**
 * Class SpeciesModel
 * @package aneclassesmodels
 * @Entity @Table(name="aneSpecies")
 */
class SpeciesModel
{
    /**
     * @Id
     * @Column(name="sId", type="integer")
     * @GeneratedValue(strategy="IDENTITY")
     * @var int $id
     */
    private $id;

    /**
     * @Column(name="sName")
     * @var string $name
     */
    private $name;

}

/**
 * Class BirthModel
 * @package aneclassesmodels
 * @Entity @Table(name="aneBirths")
 */
class BirthModel
{
    /**
     * @Id
     * @Column(name="bId", type="integer")
     * @GeneratedValue
     * @var int
     */
    private $id;

    /**
     * @Column(name="bName")
     * @var string
     */
    private $name;

    /**
     * @OneToOne(targetEntity="SpeciesModel")
     * @ColumnJoin(name="bSpeciesId", type="integer")
     * @var SpeciesModel
     */
    private $species;

}