INVESTIGATIONS INTO FERTILITY AND HATCHING SUCCESS OF HUMBOLDT PENGUIN (SPHENISCUS HUMBOLDTI) EGGS AT LONDON ZOO.

Establishment of breeding programs in zoo-housed Humboldt penguin (Spheniscus humboldti) colonies often takes several years and breeding success is generally perceived as poor. Husbandry and pathology records of eggs laid since the establishment of London Zoo's colony were retrospectively analyzed. Following a barren period from arrival of the first birds in May 2011, the first egg to hatch was laid in December 2013 and egg laying was consistent over the following 10 yr. A total of 823 eggs were laid by male-female pairs, so from 2018 onwards some newly-laid eggs were removed in order to limit population growth. Of the 556 eggs incubated by 61 pairs, 289 (52.0%) hatched. Individual females laid between one and 56 eggs across this period; over 40% of which were laid in March, generally as their first clutch of the year. Hatching was significantly affected by the time of year (p = 0.004), the laying order in the clutch (p < 0.001), and the nest type (p = 0.004), but not by the year, size of the clutch, parental age, or whether either parent had been parent or hand-reared. Postmortem examination of eggs that failed to hatch only identified embryos in 27.2%, covering a range of developmental stages. However, half of the remainder were too autolyzed for a meaningful diagnosis. More detailed, microscopic examination of 78 of the eggs from 2019-20 revealed that only six of 71 eggs (8.5%) that were diagnosed as suspect infertile on gross examination were truly infertile. In addition, two of the seven eggs suspected to be fertile on gross examination had no microscopic evidence of fertility. These findings highlight the importance of microscopic examination of unhatched eggs for accurate fertility assessment.