Bird egg fertilization

Someone told me that female birds, like chickens and such, will naturally produce and lay eggs, whether or not they’ve been fertilized by a male. If they haven’t been fertilized, the eggs simply won’t hatch. And also said that most of the chicken eggs that we eat aren’t fertilized.

Is this true? It immeadiately strikes me as counter-intuitive… a species evolving to waste resources like that (if it’s not fertilized), but it’s coming from someone I expect to know something like that…

It’s true. Except if you bought them in some little farm where hens and roosters roam freely, I doubt the eggs you eat are fertilized.
Strangely enough, on another thread someone seemed to believe the contrary : that nobody ever eat fertilized eggs.
As for the waste of ressources, I really don’t know. But perhaps in a natural state, it’s very unlikely that a hen wouldn’t be fertilized. They aren’t in egg-producing farms only because there are no males around, a situation which probably wouldn’t occur for wild birds.

Also, since the egg must exist for the fertilization to take place, either the female bird would have to “keep” the male’s sperm alive in some way until it produces an egg, either it would have to stop producing the egg if it’s not fertilized (and in the latter case, it would imply that fertilization occurs at a time when the egg is only partially formed, I don’t know if it’s the case). So, perhaps these processes would be more “ressource wasting” than occasionnally laying an unfertilized egg when no male was available for whatever reason.

Mammals, including human females, produce eggs every month regardless of whether they get fertilized or not. And in humans, if the egg is not fertilized, not only is it lost, but a lot of iron-rich tissue is lost too.

While that approach may seem inefficient, it is actually quite a good mechanism to ensure maximum chance of getting an egg fertilized and ensuring continuation of the genetic line. Such use of precious resources tips the balance towards greater probability of having a viable offspring.

Except that in chickens, its more frequent than once a month. Egg-laying chickens may produce (in their prime) up to an egg every 2 days or so - there are methods to “trick” chickens into thinking more time has passed than it really has. Chickens are very photodependent in their egg-laying, and so changing ambient light conditions on a regular schedule (8hours on, 8 hours off, 8 hours on, etc) makes their bodies think that that its time to lay an egg sooner than they would in the wild.

And yes, the large majority of the eggs we consume are not fertilized. The exception is the occasional egg produced in free-range conditions, where there is often a rooster for every 10-20 chickens (I don’t remember the ratio for sure - the rooster also contrbutes an “incentive” to lay eggs more frequently). Occasionally, an egg will be fertilised, however eggs are collected every day, and so it does not get incubated properly right away. This also causes the egg to never develop, since it needs to be maintained at specific temperatures throughout the foetal development.

If you’re interested, you can actually examine your eggs to see if they’ve been fertilised, except that the only way to tell is to break the shell (in which case it doesn’t really matter anymore, does it? :)). Break the shell, and examine the yolk. If it has a small, ring-like structure on it (maybe a half-centimeter in diameter) then it’s been fertilised. If it doesn’t, then it hasn’t. Again, this will only happen if your eggs are collected from free-range farms - battery cages don’t have roosters present.

NOTE: IANAChicken Farmer -I took a single course on animal production systems, and spent a very interesting field trip at a government funded chicken farm (as well as beef and dairy farms on other days). I just remember this from that course, so someone else might know more than I do :slight_smile:

Of course this is not an “except” as a chicken obviously is not a mammal. There is another way to tell and that is to use candle light. By the use of a candle, you can tell the structure of the yolk. This is how some restaurants brag they sell eggs with two yolks. (At least, there is one restaurant in DT Chgo that does so, if it is still there.)

As far as wasting eggs, many animals waste a lot of eggs, thousands in fact. Fish, insects, etc. will lay thousands of eggs but not all get impregnated. An of those that do and hatch, most of them don’t survive predators. Who said Mother Nature is frugal? She does what She has to do.

You have to remember that the domestic chicken is not a normal bird, but has been highly selected for certain traits by humans over thousands of years.

Although wild birds will occasionally lay eggs that have not been fertilized, this is an accident. It is no more normal than a mammal producing a stillborn young. Because it does waste resources, it is selected against in nature.

Humans have selected for this trait in domestic chickens. By choosing breeding stock from lines that produce eggs even if they have not been fertilized, humans have changed the selective equation. In addition, since laying chickens are provided with pretty much all the food they can eat, resources are not a limiting factor.

Well, my initial thoughts were that… the chicken originally had a tiny egg like humans, and if it were fertilized, it would grow into a large egg, as human eggs grow into fetuses.

It just didn’t seem intuitive to me that a chicken would grow a full size, non-fertilized egg rather than just discarding it as a tiny, unused egg like humans do.

Yeah, I can see why you’d think that, Senor Beef, but those unfertilized eggs in humans get discarded when women have their periods. I don’t think birds do that kind of thing.

Do all birds do this?

Does it cause any emotional distress to them to have their (assumably children) removed from them?

I ask because some friends have pet parrots.

I’m not sure what you mean by “do this.” As I said, although wild birds sometimes lay unfertilized eggs by accident, this is not the norm.

If wild birds lose their first clutch of eggs, they will often re-lay, especially if it is early in the breeding season. In fact, this has been a key factor in captive breeding programs for species such as Peregrine Falcons or California Condors. Fertile eggs are removed from one paired in order to replace infertile eggs produced by another pair that may have some fertility problems. The first pair will then re-lay, so you end up with two clutches being raised.

Losing eggs no doubt causes distress to the parent birds. However, it is probably of little concern to domestic chickens because of artificial selection.

Some birds will not lay eggs (regardless of whether or not they will be successfully fertilised) in the absence of certain stimuli; for example Parakeets will usually not lay eggs at all unless a suitable nest box is provided.

Senor Beef, I’ve had a few pet birds myself (thus my name), and sometimes they do lay eggs without a mate, nest box, you name it. You’re supposed to let them sit on them a while, as long as they want to, and then toss 'em once they get bored. If you take the eggs out right away they’d probably just lay more to replace them, and that would be bad for them. Deplete their calcium reserves and all that.

How do the roosters fertilize the eggs anyway?


Well, first, the rooster and the hen will have formed a loving bond and have decided to commit to a permanent, monogamous relationship, then he will usually arrange to meet with the hen’s parents to discuss the wedding arrangements…


I mean, a single female bird in captivity - will all species of birds lay large, unfertilized eggs?

Well, I’m wondering if birds inherently know whether or not they’re sitting on an infertile egg. Assumably not. So I’d imagine that a bird would consider the egg it’s developing child, and hence, removing the egg might be emotionally distressing, and cause hatred towards the pet owner, or whatever.

I don’t think they do that, exactly. They’re probably evolved to expect losing some eggs, to predators and just because they get knocked out of the nest. So they just have some more to replace them without seeming actually distressed about it.

Welcome to the boards, PK!
Some male birds have an “intromittent organ,” looking something like a penis to aid in copulation. Most, though, develop a swollen cloca (called a clocal protrubance). Birds start off with a little kiss - a “cloacal kiss” where the two vents are rubbed together very briefly. Fertilization of the egg occurs in the infundibulum {high up where the egg leaves the ovaries and enters the oviduct), and then the fertilized egg travels through the oviduct, gathering layers of albumin (egg whites), calcium and finally color (if any).

Female birds have sperm storage tubules, which allow them to carry sperm for an extended period of time - up to several (3?) months, if necessary. Eggs can then be fertilized even when males are not present. So, it makes sense to “drop and egg” every day since they are likely to be fertile. I imagine, given the proper stimuli and nutrition, that most female birds could be induced to lay unfertilized eggs in capitivity. It may not be easy to accomplish with some species, but I can’t think of a reason why it couldn’t happen.

Do birds mourn the loss of an egg or clutch? I dunno. We did have a magpie egg (wild population) that was marked in one nest show up in another. Was it stolen or deliberately moved by the parents? Birds are pretty adept at clutch reduction to insure maximum potential viability of at least some offspring. Despite this, nesting success can still be low, so one better be prepared to replace if needed.

And chickens are disturbingly gluttonous around broken eggs.