SELECT *
FROM clutches
WHERE clutch_breeding_pair = 2 ORDER BY clutch_laid_date DESC

$stmt = $dbh->query("SELECT * FROM clutches WHERE clutch_breeding_pair = '$breedingPairID' ORDER BY clutch_laid_date DESC");
$stmt->setFetchMode(PDO::FETCH_ASSOC);
$row_count = $stmt->rowCount();
$row = $stmt->fetch();

SELECT c.clutch_breeding_pair,
  ifnull(AVG(datediff(c.next_clutch_laid_date,c.clutch_laid_date)/7),0) average_weeks
FROM (
    SELECT c1.clutch_breeding_pair,
      c1.clutch_laid_date,
      min(c2.clutch_laid_date) next_clutch_laid_date
    FROM clutches c1
      left join clutches c2
        on c2.clutch_laid_date > c1.clutch_laid_date
        and c2.clutch_breeding_pair = c1.clutch_breeding_pair
    WHERE c1.clutch_breeding_pair = 2
    GROUP BY
      c1.clutch_breeding_pair,
      c1.clutch_laid_date
    ) c
GROUP BY
  c.clutch_breeding_pair

SELECT clutch_breeding_pair,
    truncate((datediff(max(clutch_laid_date), min(clutch_laid_date)) /
      IF (count(*) > 1, count(*) - 1, 1) / 7), 4) AS average_weeks
  FROM clutches
-- WHERE clutch_breeding_pair = 2 -- filter by clutch_breeding_pair
  GROUP BY clutch_breeding_pair
-- HAVING average_weeks > 0; -- remove 0 value rows

WHERE clutch_breeding_pair = 2 -- filter by clutch_breeding_pair

HAVING average_weeks > 0; -- remove 0 value rows