The value of their leather stimulates commercial farming with several crocodilian species.
The survival and growth of crocodile hatchlings depends on their birth mass. There exists
a positive relationship between the hatchling mass and egg size of several crocodilian
species. The size of crocodilian eggs is often not measured before hatching. The aim of this
study was to create a model whereby the volume of individual Nile crocodile eggs can
be estimated after they have hatched and the shell been broken, so that the relationship
between egg volume and hatchling mass can be studied on an individual basis without the
size of the eggs having been measured prior to hatching.
Infertile eggs were photographed in side view, with one pole towards the bottom and
the other towards the top and a scale in the focal plane. Their volumes were measured
by water displacement (displacement volume). A custom-written computer program was
used to measure the photo images. The program turned the image of the egg upright and
the position of the polar axis was determined without considering the position of the upper
pole. Various transverse diameters (perpendicular to the polar axis) were measured, and the
volume of the egg calculated by integrating the function describing the horizon of the egg
on the polar axis (calculated volume). The best models for estimating the calculated volume
were determined by using information limited to various distances from the bottom pole of
the egg’s image towards its upper pole, and for eggs of different polarity. The models were
then used to estimate the volumes of 138 eggs of which 15%, 20%, 25% and 30% of the image
of each egg were masked from the upper pole towards the bottom pole.
Volumes of 60–135 ml derived from analysis of the masked photographic images of
eggs permitted estimation of the eggs’ volumes to within 4.57 ml of their actual volumes
with 95% confidence. This study makes it possible to estimate the volume of eggs from
the shells of hatched eggs and identify a variation larger than 7.72% in the birth mass of
Nile crocodile hatchlings from eggs with an estimated volume of 60 ml, with the precision
increasing to identify a variation larger than 3.40% for hatchlings from eggs with an
estimated volume of 135 ml with 95% confidence.
Die
waarde van hul leer stimuleer kommersiële boerdery met verskeie spesies van die Crocodilia.
Oorlewings- en groeivermoë van krokodilbroeilinge hou verband met hul geboortemassa.
Daar bestaan ’n positiewe verband tussen broeilinggrootte en eiergrootte van verskeie spesies
van die Crocodilia. Krokodileiers se grootte word dikwels nie gemeet voordat hulle uitbroei
nie. Die doel van hierdie studie was om ’n model te skep waarmee die volume van individuele
Nylkrokodileiers geskat kan word nadat hulle uitgebroei het en die dop gebreek is, sodat die
verband tussen eiervolume en broeilingmassa op ’n individuele basis bestudeer kan word
sonder dat die grootte van eiers gemeet is voordat hulle uitbroei.
Onvrugbare eiers is in sy-aansig gefotografeer, met een pool na onder en die ander
na bo en ’n skaal op die vlak van fokus. Hul volume is met waterverplasing gemeet
(verplasingsvolume). ’n Rekenaarprogram wat vir die doel geskryf is, is gebruik om die
fotobeelde te meet. Die program het die eierbeeld regop gedraai en die posisie van die
poolas bepaal sonder om die boonste pool se posisie in ag te neem. Die lengte van verskeie
dwarsdeursnitte (loodreg op die poolas) is gemeet, en die volume van die eier bereken
deur die funksie wat die horison van die eier op die poolas beskryf te integreer (berekende
volume). Die beste modelle is bepaal om die berekende volume te skat deur gebruik te maak
van inligting beperk tot verskillende afstande van die onderste pool in die rigting van die
boonste te gebruik, en vir eiers met verskillende polariteit. Die modelle is daarna gebruik om
die volumes van 138 eiers waarvan 15%, 20%, 25% en 30% van elke eierbeeld, van die boonste
pool in die rigting van die onderste, gemaskeer is.
Deur analise van die gemaskeerde fotobeelde kan die volume van eiers met volumes
van 60 ml tot 135 ml met 95% vertroue binne 4.57 ml van die werklike voorspel word.
Hierdie studie skep die moontlikheid om die volume van uitgebroeide Nylkrokodileiers te
skat. Variasie in Nylkrokodille se geboortemassa van groter as 7.72% kan met 95% vertroue
geïdentifiseer word vir broeilinge uit eiers met ’n geskatte volume van 60 ml, terwyl die
presisie verbeter tot ’n variasie groter as 3.40% vir broeilinge uit eiers met ’n geskatte volume
van 135 ml.
