GHARIAL: MAIDEN CLUTCH AND NEST SITE STRATEGY
Background to this blog. On May 19, 2021 28 gharial hatchlings were observed with a female in Satkoshia Gorge of river Mahanadi, Odisha state. The river stretch is in Satkoshia Gorge Sanctuary (1976) that was constituted under and a part of the national crocodile conservation project of Government of India launched with support from UNDP/FAO.
While I congratulated the officers who have ensured to regulate habitat disturbances by people, I also mentioned that 28 hatchlings mean it is not the maiden clutch, and that the reproductive effort of the female in previous year(s) had remained unnoticed.
This prompted me to look back on my data and interpretations on two subjects:
(A) What is the minimum clutch size? (1.) In my PhD dissertation (Singh 1978, Table-11) I provided data on 27 nests from rivers Narayani and Kali, Nepal relating to the years 1976 and 1977. Out of these, six nests had less than twenty-five eggs. As a practice in hatchery incubation, nest-wise we examine all unhatched eggs. There were three completely infertile nests with 10, 16 and 24 eggs. Out of the remaining three nests with 12, 18 and 16 eggs, the hatching success were 75, 16.7 and 50%.
(2.) Sunil L. Rajbhandari and Paras M. Acharya (2015, Report to Rufford) have reported the smallest clutch with just 6 eggs in 2014 and 18 in 2013, both at different places in Narayani river.
(3.) Tirrtha M. Maskey (PhD thesis, 1989), studying in Nepal, reported the smallest egg clutch of 16 in 1977, 18 in 1978, 14 in 1979, 14 in 1980, 30 in 1981, 31 in 1987. So, some movement or pushing out of the main congregation may be occurring to reduce competition in resource partitioning.
(4.) Khadka et al (2020, Herpetologica) have provide data on 151 Gharial nests over 17 years in sand banks along the Narayani (n = 94 nests) and Rapti (n = 57 nests) Rivers in Chitwan. Based on the range of clutch size given, the year-wise smallest clutch was with 21 eggs (2003), 11 eggs (2004), 23 (2006), 19 eggs (2010), 23 (2011), 7 (2012), 23 (2013), 6 (2014), 12 (2015), 16 (2016), 19 (2017),
(5.) Our team in Chambal observed 17 and 24 eggs as small clutches around a communal nesting site in 1985 (Rao and Singh 1992), but had not traced the season when they might have joined the congregation.
(B) Where does the gharial lay maiden clutch of eggs? A mother gharial with her maiden clutch is smaller in size and lower in the hierarchical order. Such mothers may not find access to better nesting locations or communal nesting stretches used by mother gharials larger in size.
Such territorial behaviour at nesting site is seen from the time the ‘trial pits’ are dug before actual nest holes and laying of eggs. At a communal nesting site, the dominant mother takes possession of all hatchlings; others remain around, and the dominant male also joins in creche guarding. Perhaps it takes a couple of nesting seasons before a maiden mother is able to join the communal site.
Conclusion The clutch size can be as small as 6. Small clutches with 75% hatching success can be 12. Such small clutches will in all probability be away from communal nesting sites, for behavioural reasons and for reproductive success by the young females in the hierarchal order among gharials.
KEY WORDS: Gharial, Gavialis gangeticus, minimum clutch size, adaptation by young breeding female, hierarchal pattern
