1. Baby Pigeons Are Rarely Seen: What Is Special About Their Chicks?
You often see pigeons in parks or near stations, but few people have seen a fluffy baby pigeon. According to an article by the Audubon Society in the United States, rock doves stay in the nest relying on parents for food and protection. By the time they leave the nest, they are the same size as adults and have fully grown feathers [6]. Even though they are still children inside the nest, they look almost exactly like their parents when they go outside. So what do newly hatched chicks look like, and how do they spend their time? Bird chick development is generally divided into two main types.
2. Precocial Chicks: Why Mallard Chicks Can Walk Right After Hatching
The first type of development is called precocial. Chicks hatch fully feathered and can walk right away [1]. Examples of Japanese birds in this category include pheasants, mallards, and plovers. They find their own food, while their parents generally keep watch nearby [2]. For mallards, only the female incubates the eggs, and chicks hatch in 26 to 28 days. After hatching, once their feathers dry, the chicks immediately leave the nest and follow the female parent. A single clutch contains 10 to 14 eggs [3]. These chicks grow inside the egg until they are developed enough to walk and follow their parent. What does the second type look like?
3. Altricial Chicks: How Naked Sparrow Chicks Depend on Parents' 4,000 Feeding Trips
The second type is altricial. Chicks hatch without feathers and cannot move right after hatching [1]. Examples in Japan include sparrows, swallows, and pygmy woodpeckers. They receive food from parents and grow in the nest for two to three weeks [2]. Sparrows lay 4 to 8 eggs at a time. Incubation lasts about 12 to 14 days, and the time from hatching to leaving the nest is about 13 to 14 days. However, the number of days varies depending on the source, so a range is given here [4]. During these two weeks, parents are said to catch and deliver insects more than 4,000 times [5]. Dividing the 4,000-plus trips by 14 days gives more than 280 trips per day. However, it is not clear from the sources whether this count is for all parents combined or per parent. Chicks also stay near their parents for about 10 days after leaving the nest before becoming independent [5]. Precocial chicks grow fully inside the egg, while altricial chicks are raised by parents bringing food. Where does this difference come from?
4. How Much Egg Yolk a Bird Egg Has and How Mature the Chick Is at Hatching
Precocial chicks grow inside the egg until they can walk. Therefore, the egg needs more nutrients. In a study of bird eggs by Sotherland and Rahn in 1987, the abstract states that as the proportion of yolk increases, the degree of maturity at hatching progresses from altricial to precocial [7]. An explanation from Stanford University also notes that precocial eggs can have up to about twice as many calories for the same weight [10]. Please treat "up to" as a rough estimate. Beyond just egg nutrients, research suggests that brain development is also involved in the difference between these two types.
5. Brain Growth in Precocial and Altricial Chicks: Nutrition from Eggs or from Parents
A review of birds published around 2017 introduces an interesting comparison regarding brain size. At hatching, the brain of precocial chicks is larger, but as adults, altricial birds have larger brains relative to their body size [8]. It is explained that precocial brain development progresses inside the egg, while altricial brains grow after hatching, also in relation to food brought by parents. This relationship is not seen in mammals. This does not mean "altricial birds are smarter." It is strictly about brain size relative to body size. In an analysis of many species (a peer-reviewed paper), parental provisioning (whether the bird is altricial, relative egg weight, length of feeding period, etc.) was closely linked to relative brain size [9]. However, this is a correlation, and causation cannot be confirmed. So far, we have looked at two clear boxes. Are there birds in between?
6. Semi-Precocial and Semi-Altricial Birds: Types Between the Two Extremes
In reality, the two types cannot be cleanly separated. A list from the Abiko City Bird Museum shows that the oriental turtle dove and owl are semi-altricial, while the coot is semi-precocial [2]. Clutch sizes also vary: mallards lay 10 to 14 eggs, pheasants 6 to 12, and swallows 4 to 6 (sparrows are 4 to 8, as mentioned in Section 3). In research, precocial and altricial are treated as a continuous "spectrum." At the ends are super-precocial birds that are fully independent immediately after hatching, and super-altricial birds that are born naked with closed eyes [8]. Stanford University’s explanation notes that there are stages even within precocial birds; for example, grebes follow their parents but still receive food [10]. Knowing these differences, how do we see the birds around us?
7. How to Check a Bird's Chick Type Yourself
What you can do today: Choose one common bird and predict: "Do its chicks walk immediately after birth, or do they wait for parents in the nest?" Then check with an encyclopedia or official materials. Even if your prediction is wrong, looking at the number of chicks and how parents care for them can reveal why it is that way. What you can do when you go out: If you see waterfowl with chicks at a park pond, observe from a distance. You can see if the chicks are following the parent or finding their own food. Please do not approach or touch the chicks or nests. Official information: The Abiko City Bird Museum’s "Tegatan" has a list summarizing how Japanese bird chicks grow [2].