Altricial eaglets rely on parental care until they fledge. But goslings are precocial: capable of moving around, self-feeding, and leaving the nest shortly after hatch. What does that mean? Read on to learn more!
Canada Geese and Bald Eagles: Precocial versus Altricial
From Stanford University: A precocial bird is “capable of moving around on its own soon after hatching.” The word comes from the same Latin root as “precocious.” Altricial means “incapable of moving around on its own soon after hatchling.” It comes from a Latin root meaning “to nourish” a reference to the need for extensive parental care required before fledging in altricial species. So what’s the big difference? Precocial birds are more developed than altricial birds at hatch: able to move around, feed themselves, and often swim or dive for short periods of time. Altricial birds hatch helpless: unable to see, move around, or find their own food.
Why are precocial birds ‘older’ at hatch than altricial birds? Precocial birds like Canada geese lay energy-rich eggs that accelerate the in-egg development of their young. Their large, energy-rich eggs may contain almost twice the calories per unit weight than the eggs of altricial birds, which means that precocial females must obtain abundant food resources before laying eggs. Altricial birds like bald eagles and peregrine falcons do not have large nutritional demands before egg-laying, but they have to find sufficient food once their helpless young hatch.
Precocity and Brain Development
Precocity affects brain size and development inside the egg and later in life. Precocial species have relatively large brains at hatching, but their adult brains are smaller relative to body size (the brain/body-mass index) than those of altricial birds. While altricial young hatch with smaller brains, they have highly efficient digestive tracts and a rich, parent-provided diet. Their brains grow post-natally and adults have proportionally larger brains than precocial species. Is this because they have more energy available to grow larger brains, or is something else going on? We’re still trying to figure it out. This article discusses the relationship between a long childhood and intelligence in crows: https://www.smithsonianmag.com/smart-news/long-childhood-may-be-how-these-birds-got-so-smart-180975065/.
At any rate, our hatchlings face very different challenges. Precocial Canada geese are relatively mature and mobile from the moment of birth. Eagle and peregrine parents bring food into the nest for their young, often caching or storing prey for later consumption. Their young don’t need to leave the nest or procure food until they fledge. The young goslings leave the nest within 24 hours of hatching and do not return to it. While their parents continue to provide protection and care, the goslings feed themselves.
The precocial goslings are also able to thermoregulate right away, unlike the eaglets and owlets. Altricial birds require their parents (or a parent) to apply warmth until their down feathers are developed enough to insulate them. The eagle parents and mother owl will spend a great deal of time huddling over their young after they have hatched, but the geese in Decorah will take to the water quite quickly, with no huddling required. Follow this link to watch the geese and keep up with the latest from the Decorah Canada Geese: https://www.raptorresource.org/birdcams/decorah-eagles/.
Worried about the jump? Here’s a video of Canada geese jumping from the Charlo Osprey nest on explore.org back in 2020!
Stanford University, Altricial and Precocial: http://www.stanford.edu/group/stanfordbirds/text/essays/Precocial_and_Altricial.html
Patterns of Metabolism and Growth in Avian Embryos
Carol Masters Vleck, David Vleck and Donald F. Hoyt
American Zoologist , Vol. 20, No. 2 (1980) , pp. 405-416
Published by: Oxford University Press
Article Stable URL: http://www.jstor.org/stable/3882403
The Evolution of Parental Care in Birds
A. Ar and Y. Yom-Tov
Evolution , Vol. 32, No. 3 (Sep., 1978) , pp. 655-669
Published by: Society for the Study of Evolution
Article DOI: 10.2307/2407731
Article Stable URL: http://www.jstor.org/stable/2407731
Developmental Modes and Developmental Mechanisms can Channel Brain Evolution