Subject:         [BIRDCHAT] answer to egg to bird size ratio
Date:         Tue, 14 Apr 1998 08:15:53 -0400
From:        "Felton, Gary L"
To:         BIRDCHAT@LISTSERV.ARIZONA.EDU

This was the question I initially asked.  What bird lays the largest egg in comparison to it's body size?  Is it the Hummingbird ?

Below are the responses I received.
 

  •  Traditionally, the kiwi (various species) has been touted as having the largest egg relative to its body size.


Anthony Lang, Ph.D., Ecologist,
Burlington, Ontario, Canada
 

  • I think it's the Kiwi from Australia.  I believe I've read about that fact a couple of times, but I can't cite any specific sources.  I'm sure that any book that mentions the kiwi also mentions this unusual fact about it.


Andy Rabin
Gaithersburg, MD
 

  • I think that it may be the Kiwis that have the largest egg in comparison to its body size.  (If not, it is close)  It is truly unbelievable to see an x-ray of a female Kiwi with an egg!! Almost her whole body!  Also, the young retain a good amount of the yolk inside themselves when they hatch, so that they have sufficient nutrients until they learn to forage for food for themselves.


Jeremiah Trimble
New London, CT
 

  • Without taking a huge amount of time to research this one, I believe it is the Kiwi.  Kiwi eggs are at the time of laying about 1/4 the weight of the adult.  However, the bee hummingbird's egg is also about 1/4 the weight of the adult bird.  Yet another source I have says that the kiwi egg is 1/3 the weight of the adult bird.  Going with either kiwi or bee hummingbirds is a safe bet.


Ellen Paul
Chevy Chase, Maryland
 

  • I believe the record-holders are the kiwis; kiwi eggs can reach 25% of the body weight of the female.  Kiwi eggs also hold the record for the largest proportion of yolk to egg volume - some 60%, probably related to their long incubation time.  The Handbook of the Birds of the World (vol 1) notes that kiwi eggs are four times the size of that expected for a bird of its body weight.


Ronald I. Orenstein
Mississauga, Ontario
 

  • I thought it might be the Kiwi which lays a relatively huge egg, but it turns we are both correct.  Hummingbirds lay the smallest eggs, but they average about 25% of their own body weight while Ostriches lay the largest eggs which are only about 1% of their weight.  It turns out there is a general rule that egg-weights are proportional to female body weight raised to the power of 2/3.  Thus large species lay relatively smaller eggs.  Also precocial species lay larger eggs than altricial species.


Kiwi eggs vary from 18-25% of the female body weight depending on the species; thus comparable to hummingbirds.  But since Kiwis can lay clutches of up to 5 eggs compared to the hummingbird's two eggs, I think the kiwi should get a special award.
Source:  "A Dictionary of Birds" by Campbell & Lack (1985)
Joseph Morlan
Pacifica, CA 94044
 

  • I'm pretty sure it's the Kiwi from New Zealand.  If I remember, the egg is up to 1/2 the weight of the bird, and 1/3 the volume! Take care.


Allen Chartier, Inkster, MI
 

  • Gary, some of the Kiwis lay eggs about 1/4 of the weight of the bird if I recall correctly.


John Miles
Jarvis, Ontario
 

  • The Puerto Rican Tody lays an egg that is 26% of the body weight of the female.  The other 4 tody species are probably in the same ball park.


Fascinating!  I just checked Campbell & Lack and they state (pg 597)  "In the Puerto Rican Today T. mexicanus, each egg represents 39% of the bird's body weight (birds average 5.4g and eggs 1.4.g)."  But when I calculate that ratio I get your 26%, not 39%.  Still a record, egging out <groan> the Kiwi by 1%.
This section was written by A.K. Kepler who cites his own monograph
"Comparative Study of the Todies (Todidae): with Emphasis on the
Puerto Rico Tody, Todus mexicanus. Cambridge, Mass."
Joseph Morlan
Pacifica, CA
 

  • I am afraid that all of you are wrong.  I have it on good authority from one of my second graders that the Mary Poppins Bird, which weighs five pounds and is ten feet tall, lays an egg ten times taller than her--that is one humungous egg!  The bird eats cloth and spits silk back for a nest. This bird lives in Arizona and is very well-camouflaged for its


environment which, of course, explains why no one has ever seen it!
Judy Pike

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