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Thread subject: Sunday's Tutorial
Name Date Message
Marie 05/15/05 12:23 pm Precocial chick versus Altricial chicks.

There are two types of hatchlings. Precocial or Altricial. This means that precocial chicks hatch with their eyes open and have a thick coat of natal down. They can stand quickly and walk away to feed themselves. They often leave the nest within one to two days. Most shorebirds, gamebirds including the domestic chicken and ducks have precocial hatchlings.
On the other hand Altricial chicks hatch blind, and virtually naked. Thye require long periods of feeding and brooding before they are strong enough to leave the nest. Most tree and cavity nesting birds have altricial young. Apparently precocial egg laying birds lay much bigger eggs and they are loaded up inside with lots of nutrients. The hen's investment before egg laying of precocial chicks is a greater investment than those of birds that are relatively secure within a cavity or higher placed nest in a tree. Predation is apparently far less when nesting is off the ground. Those little chicks you see running around that represent an almost exact image of their parents are often only 24 hrs old. ie the Killdeer for one. So when we consider the alticial chick , it can afford to hatch from a smaller egg and take a much longer period for development. So the big question is.......
What kind of hatchling do OSPREYS have?
RonS 05/15/05 12:38 pm Does this fall into the trick question category? The Osprey chicks are wide eyed and covered with down, but they are certainly not able to feed themselves nor can they leave the nest anytime soon after hatching. Is there a "blend" category of 50/50 or something?
Marie 05/15/05 12:48 pm Well Ron...your observations are correct. As far as I know the Ospreys fall in the catagory of Altricial...there are always exceptions to the standard rule. These exceptions are called skews, a sort of distortion that throws everything off including ME.
So there you have it........I am afraid it is either one or the other at this time......P ' v ' A
Celeste 05/15/05 01:05 pm I would say Altricial also.....Carpenteri's-The Fish Hawk Osprey describes newborn osprey chicks arriving weak, wet and helpless, entering the world 1-2 days after they first begin pipping the shell. As Ron indicated, covered with down and their eyes open within hours of hatching, at which point they begin taking frood from the parents. Ten days after hatching, the chicks develop a 2nd coating of light down, and the crop soon bulges with food, which allows the osprey parents more free time between feedings than most other birds. For the next two weeks, osprey chicks enter what is referred to as "reptilian stage", in which they are black, scaly looking and aggressive toward each other. Changes in coloration starts, with a light tan streak which runs down the chicks' backs, and their feet become bluish gray with long, black claws. At 2 wks feathers appear on the necks and head of the chicks. Darker body feathers follow, with "primaries, secondaries, and wing and tail feathers devoloping at 3 weeks of age. Within 30 days of hatching, young ospreys have increased in size to about 75% of their adult body weight.
In reading about the chicks development I found the following interesting about the male osprey parent. Males usually spend less then 35% of their day foraging and this may have some impact on chick survival. According to Carpenteri, researchers have not discovered why male ospreys are "lazy", but it may be more a question of "ensuring the survival of the adult breeders than any lack of ambition on the male's part."
Marie 05/15/05 01:21 pm Wonderful Celeste...great to recap the stages of our osprey chick development. You and Cecelia have great reference books on the Osprey. I must try to get one too. If I recal correctly TIGER has a good one too.
Cecilia 05/15/05 06:10 pm Oh dear...what a good question! And of course I went to Poole (alright...I know you are all sick of me quoting Poole but he remains the gold standard for these discussions) and here's what he says: (Ron - you get the best in class star :-)

"Ospreys enter the world weak, wet, and relatively helpless. The strongest part of a newly hatched Osprey is it's neck, which helps drive it's egg tooth, the hardened tip of the upper mandible (beak), into the confining eggshell. If you handle a hatching egg, you are likely to hear the chick's faint peeps within and see the tapping of a persistant bill through a hole in the shell.

Most Ospreys hatch within one or two days of pipping their shells. Like other birds of prey, they emerge as 'semi-precocial" young. This means that down covers most of their body, that their eyes open hours after hatching, and that they can actively take food from their parent's bill."

So...they are straddling the fence betwween Altricial and Precocial...almost as Ron said...a"blend"catagory:
"semi-precocial".



Marie 05/15/05 06:19 pm Excellent detective work Cecelia......thanks for setting the record straight....so we have that skew called semi -precocial. Could it mean there maybe a catagory called semi-altricial too?
cathy 05/15/05 07:27 pm Thanks for the good information. I am learning alot!

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Tom Throwe
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