For the experts: Are juveniles actually smaller than adults?

For the experts: Are juveniles actually smaller than adults?

Joined: May 22nd, 2008, 11:02 am

August 10th, 2017, 12:43 pm #1

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
Wilmington, Delaware (USDA Zone 7a)
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Joined: August 21st, 2012, 2:43 pm

August 10th, 2017, 1:36 pm #2

Ron, I'm no expert and my eyes aren't what they used to be but I don't think size necessarily means much. Generally light colors make objects appear larger, dark smaller. To my eyes all immature birds look to be the same size. Adult females I believe are, in fact slightly larger and I believe its noticeable when alongside immature birds. The difference between adult males and immature birds is pretty hard to explain except for the darker overall coloration of the male makes him appear smaller than the lighter coloration of the immature birds.
Just my thoughts on the subject maybe Nan might have a comment?
Joe M.
Lakeland, FL
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Joined: May 21st, 2013, 12:09 am

August 10th, 2017, 2:34 pm #3

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
They can look smaller especially when their tails haven't grown to their full length and it appears that often their bills have a ways to go after fledging. I am pretty certain about the tails which often look forked until the central tail feathers catch up and a bit less so about the bills. Generally I agree with your impression. Sometimes I have to get out my binoculars to prove to myself I am not seeing a Calliope.
Southern New Jersey
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Joined: June 21st, 2006, 1:24 pm

August 10th, 2017, 4:57 pm #4

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
I'm not an expert, but I always thought the juveniles (when they are at the point of fledging from the nest and afterwards) could actually be larger than the adults, especially the mother, since they have been in the nest resting and eating and the mother has been working so hard to provide for their needs. Again, though, as someone mentioned, size is difficult to gauge because of lighting, temperature (a bird that is cold is fluffing out its feathers and could look larger without actually being larger), etc. I think the only way to really determine this is when a bander might weigh and measure a bird.
Madison, WI
Zone 5a
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Joined: August 21st, 2012, 2:43 pm

August 10th, 2017, 7:27 pm #5

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
I doubt anyone can judge a birds weight by observing it visually. From all the evidence most fledglings leave the nest at a weight at or above their normal adult weight, thanks to the mother sacrificing her needs for the fledglings.

The vast majority of hummingbirds observed in mid to late summer are fledglings, the ratio is probably as high or greater than 10-1. For me, trying to identify the age of a bird by size is somewhat deceiving so I don't even mention it as an identifying feature.
Joe M.
Lakeland, FL
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Joined: May 29th, 2015, 2:19 am

August 10th, 2017, 8:46 pm #6

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
Well, I sure hope for lots of info on this subject. My thoughts are based on what I have seen at my feeders but I could just be imagining.

I use two kinds of feeders (first nature and the old PP) I have noticed the tail on some birds seem to way over hang the "perch area ring" on the first nature. I also have noticed some birds almost fit within the PP plastic flower....you do not see their bodies or any tail when feeding, really appear to have a much smaller body and shorter tail than other hummingbirds who visit it. When looking at the profile, the beaks do seem shorter on the smaller birds.

Also, smaller birds seem to spend much, much longer sitting, looking around and observing who knows what?? But, just seem to be looking above, side to side, fly a bit up and down on the perch as if testing it a few times jump and flapping their wings. Again, the beaks appear smaller on those that have this behavior.

Last year, two a juvenile male (?) (very heavy dark strips on neck) and a juvenile female (?) used the feeder together and would sit often together in a bare tree branch I had wired by another feeder in the yard. This I observed more than once. This year, again a pair use flowers within very close range and have seen them sitting near each other up in a tree

Perhaps, they are not juvenile hummingbirds. I am happy to have them pay a visit just the same. Sure hope for lots of comments!

Marilyn
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Joined: May 13th, 2014, 7:35 pm

August 11th, 2017, 12:23 am #7

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
Pics from Marilyn:




Alex
Northlake, IL
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Joined: May 29th, 2015, 2:19 am

August 11th, 2017, 5:02 pm #8

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
Above this message on this posting are two photos. I tried to find two photos of hummingbirds I have seen at the same feeder (sitting near the same position) at the feeder. I think Ward, this is what you are referring to when you say the tail feathers are shorter and beak appears to be shorter too. I do have a much better photo showing the traits Ward mentioned (the bird is looking front and shorter beak shows) but I have not been able to get it loaded onto the forum, I am trying to learn how but not real computer knowledgeable. Another forum member helped me with the others (thank you Alex).

I really hope for others to share their thoughts and I thank all of you for the information shared thus far. So many of you out there have a wealth of knowledge and years of observations watching these amazing birds. Many (like I) hope to learn from all of you as we share the same love of these wonders of nature.

Marilyn
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Joined: August 21st, 2012, 2:43 pm

August 11th, 2017, 6:56 pm #9

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
My last comment on this topic (I think)!
From my readings of hummingbird identifying features I do not recall any guide that mentions "size" as an identifying feature when identifying immature birds.
Maybe the experts have missed something but it seems none are willing to use it as a defining, determinate feature.
Joe M.
Lakeland, FL
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Joined: May 21st, 2013, 12:09 am

August 11th, 2017, 7:20 pm #10

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
I agree, but it also depends what you mean by size. My point was that a young bird without fully grown tail feathers will look smaller but by any other measure isn't.
Southern New Jersey
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Joined: May 19th, 2013, 3:18 am

August 11th, 2017, 8:40 pm #11

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
Ron, when they leave the nest immature Ruby-throateds are about the same size as the adults - sex for sex. Female Ruby-throateds are slightly larger than males. Some young birds will have bills that are slightly shorter than that of the adult of the same sex, but that condition does not last long after fledging. Immature males are actually larger than adult males because the wing and tail feathers of adults are smaller than those of immatures.

I do not use the term 'juvenile' because it is incorrect for hummingbirds, which do not have a juvenal plumage like the spotted breasts of American Robins and Eastern Bluebirds.
Nancy L Newfield
Casa Colibrí
Metairie, LA
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Joined: May 18th, 2013, 9:33 pm

August 12th, 2017, 8:02 pm #12

I was watching what I thought was a juvenile Rubythroat this a.m., right out my window. I could swear it seemed smaller than the adult male I saw a few minute later... So, are there really size differences like that or is it just my imagination?
This hummer on guard using my audubon window hanger, cute.



Steve W.
Martinsville IN.
Zone 6
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