hummingbirds - Colibri?

I participate in a trivia contest in a local pub. Last night, one of the questions was “How many eggs does a hummingbird lay in its lifetime?”. Answer - 2. My immediate reaction was “huh, doesn’t that mean a decrease of hummingbirds with each generation unless there’s a 100 percent survival rate?”. Somebody else said “What are you assuming about the proportion of male and female hummingbirds?”, which I conceded, but it still sounds suspicious - that would mean a scarcity of males who mate with multiple females to make that work. Nice for the male hummers, maybe, but something sounds wrong with that picture. Another thought I’ve since had is that somebody calculated that statistic COUNTING the males, so that it’s actually 4 per female in its lifetime.

So, how many eggs DOES an average female hummingbird lay in its lifetime, and where did the quiz preparers get that factoid?

That trivia answer was completely wrong. It’s probably based on a simple misunderstanding. Virtually all hummingbirds lay two eggs per nest. However some ( perhaps many or even most ) hummingbirds will raise multiple broods in a single season. The Anna’s Hummingbird has been known to raise three. And hummingbird lifespan’s seem to run in the 8 - 12 year range. So even assuming the short end of the lifespan at 8 years and only one brood a season, a female would still produce a minimum of 16 eggs in the course of her life. In reality the real number would be almost certainly larger.

It should be noted that male hummingbirds are, in fact, polygynous. The generally show no interest in the female after mating and take no part in the raising of nestlings. Oddly enough, it usually seems to be females that seek out males for mating, rather than vice versa. Sweet :smiley: .

  • Tamerlane

Yeesh. Talk about tortured syntax :rolleyes: . “…would almost certainly be.”

  • Tamerlane

The little I know:

  1. Males are promiscuous, like you suggest (males mate then disappear to find more females).
  2. I think there are also an uneven distribution of the sexes, but I’m not sure if it was shown that males disperse at a different time/route or if it reflected a true difference.
  3. I think females tend to lay 2 eggs in a brood (at least NA females).
  4. I also have no idea what the average lifespan would be (although the Bird Banding Lab reports the extreme end for NA hummingbird species to vary between 6 and 12 YEARS).

So, assuming that hummingbirds average 3 years, and they’re not reproductive until their second year, then the female lays 4 eggs in those two remaining years. Either the answer reflects the male or there is a 50% mortality rate. Personally I’d add another year on and jack up the mortality rate.

Wow, Tamerlane, I didn’t realize hummers re-clutched. Three times even? I’m impressed and surprised. Perhaps my impression of high nest mortality is wrong too. Guess I’ll stick with corvids. (Sheesh, I feel like I’m chiseling stone rather than posting electrons, it’s slow on my end of the board. I thought I was posting right after yabob.)

Brachyrhynchos: Well, yes - I guess I was being a bit overly optimistic :wink: . I’ll grant that it may take a year to reach sexual maturity ( I actually can’t find the answer to that one right now ). And my 8-year projection was an optimum and doesn’t take into account average lifespans due to morbidity from causes other than old age.

But I still think the people that wrote that trivia contest were flat-out wrong and just confusing eggs per brood with eggs per life. Not only do many/most hummingbird’s raise multiple broods in a single season, but some have been known to raise two different broods in two different nest simultaneously ( though generally staggered a bit ).

It may be true that certain sources of morbidity, like predation, are probably not quite as intense for hummers as they are for other types of birds. But I simply can’t swallow the idea that they would survive as a group if every individual averaged just two eggs ( some of which will be infertile ) over their lifespan.

  • Tamerlane

Yeah, 2 does seem pretty low, but I was under the impression (clearly wrong) that they had low nest succession. I’m probably seeing them through passerine eyes. And now I am really impressed if they are able to carry off two nests simultaneously. Is this a particular species? Does the male help at all? I know, for Black-billed Magpies (or, I guess they’re now called American Magpies) that even simple mate abandonment can be enough to lose the nest. For a female hummer to bring off two nests simultaneously…WOW!

(Which for some reason brings to mind that old joke about seeing the red-tailed chased by a crow, chased by a mockingbird, chased by a chickadee - and if your glasses were powerful enough, you’d see them all chased by the hummer.) :slight_smile:

Brachyrhynchos: Slow as hell on my end, as well :smiley: . But it was good that your post reigned in my implausible scenario. And you can’t go wrong with Corvids. By the way - Great user name. I know someone that goes by Corvus :wink: . Did you know there is an Anser brachyrhynchus( with the u)? It’s a Pink-Footed Goose. Confused the hell out of me years ago when I was trying to look up an article in Zoological Abstracts for somebody.

Yeah, I think hummers are pretty prolific critters all in all. I certainly have no shortage of them locally ( the fact that everybody and their maiden aunt has a feeder hung out probably helps :wink: ).

  • Tamerlane

Thank you, O Great Khan! Tamerlane got it pretty much exactly right. I would only hope I might do half as well on a question on the Golden Horde! :smiley:

I saw exactly the same nonsense recently in that great reference work Uncle John’s Bathroom Reader, and I bet that’s where your trivia contest got it from. It’s completely false.

Virtually all hummingbirds, tropical and temperate, lay only two eggs per clutch. Actually most tropical birds only lay two eggs per clutch, while many temperate zone ones lay more. Why exactly this is so is controversial. It is also unknown why temperate hummers lay only two eggs, although it is likely because they are descended from tropical forms.

Hummers, like most birds, will lay two or more clutches per year if time and food resources permit. This is of course more feasible in the tropics where the breeding season is longer.

Hummers are very long-lived for such tiny creatures, and have frequently been documented to live more than 10 years. A female of course will try to breed at least once per year, and more often if possible. So the potential lifetime reproduction could easily be in the range the Tamerlane suggests, although of course the long-term average will be only two surviving offspring per female (as it is in any species where the population is near carrying capacity.)

In almost all hummingbirds, the male takes no part in raising the young. (There are a couple of species in which male care has been documented, but they are definitely an exception.) I would call the mating system “promiscuous” rather than polygynous. Males often perform elaborate flight displays to court females. Some have modified wing feathers that make a special buzz during courtship display. And some tropical forms sing interminably from perches to attract females (though it is very hard to recognize it as “song” since it is so high pitched.) In most species the females probably do come to the males rather than vice versa.

I assume the sex ration at fledging is 50:50, but what the ratio is among adults is very difficult to determine, since males are usually much more conspicuous, and males and females may have somewhat different ecologies (males being territorial at flowers, while females forage more widely). Males are often much more common in collections, but that is probably due to collecting bias.

Well as far as simultaneous brooders, it’s apparently been observed in Black-chinned, Ruby-throated, and White-eared hummingbirds. The three anecdotes I have cited in the book I have here include: 1.)A Ruby-throated that had two nests about 4 feet apart. One contained eggs which she incubated, the other held a brood which she fed and defended. And 2.) A Black-chinned female that began building a nest 40 feet from her first, that already held hatched chicks. After they fledged, she incubated the second family. And 3.) Another Black-chinned which is just cited as raising three broods in a season, two simultaneously.

In addition Blue-throated and Allen’s hummingbirds may nest nest more than once a year and the Anna’s apparently often nests three times. I’ve personally seen an Anna’s nest twice in one season and raise two broods, one right after the other in different nests in the same tree. The source I’m using ( which is more of a general reference ) speculates that it is quite possible that virtually all species may have multiple broodings under the right circumstances and it just hasn’t been documented yet.

As far as the males go - Apparently they virtually never help out. And the virtually is just in there because there are a handful of reports of males helping out. But those are likely bogus. Some females develop male-like plumage and the sex can only be determined by dissection.

  • Tamerlane

Colibri: Thanks for the confirmation :slight_smile: . I had/have no idea just what the mortality rate for hummers would be. But even though lots of things are listed anecdotally as having been seen to eat them, I just can’t imagine they’re very heavily predated. Seems an awful lot of work for a mighty small meal :smiley: . You would think many hummingbirds would lead nice, long, productive lives :stuck_out_tongue: .

And aha! So there is actually a standard trivia reference that lists this bit of misinformation.

Ignorance disspelled, once again :slight_smile: .

  • Tamerlane

I’ll have to look up the mortality rate, but as I recall survival was quite good for banded migrant Broad-tailed Hummingbirds in Colorado. The problem in monitoring longevity is that HBs are very difficult to band - the bands have to be custom made, and their legs are so short they are difficult to put on (I know!). So there is very little data, especially on tropical ones.

There is a whole subgenre of bird literature I like to call “A Bug Ate My Hummingbird!” - usually short notes about them falling victim to praying mantids or sometimes large tropical spiders. (And sometimes bullfrogs or trout, or getting stuck on thistles.) But these are just anecdotes, and may not reflect any serious source of mortality. Being both tiny and fast, HBs are mostly just not worth it for most predators.

However, there is a tropical hawk called - I kid you not - the Tiny Hawk (Accipiter superciliosus) that supposedly sometimes specializes on territorial male HBs, making the rounds of various flower patches until it nails one.

Thanks for the info, guys! I’ve been involved with mostly corvids and some larids and multiple clutching just doesn’t play as part of their reproductive strategy (well, maybe with southern Corvus but not here in NJ). They may do a replacement clutch should the first one disappear, but no late season clutches. The kids seem to be kids for a long period of time and despite helpers, they’re less likely to make it to their first year than not. After that, of course, their mortality rates drop (especially outside of hunting season and West Nile zones).

Now this I would like to see. Love that binomial.