Warmer weather is causing some bird eggs in Australia to begin embryo development without incubation by the hen. A recent article in the magazine “Australian Geograhic” reported that “climate change is causing bird eggs to hatch early.” This is not good.
The problem was seen in nests of Zebra Finches. Eggs of this and most bird species usually are laid one per day, in sequence. Incubation is begun when the final egg is laid. This assures hatching of all eggs very close to one another. That means all chicks are the same size, with the same strength, and thus compete equally for the food delivered by the parent birds.
However, researchers found that high air temperatures in one part of Australia were causing eggs laid early in the sequence began to develop before incubation by a parent bird began. These eggs hatched first, giving those chicks a head-start in growth. This put chicks hatching later at a disadvantage. Some of them starved because they could not compete on an equal basis for food.
The paper, published in “Royal Society Open Science” also discussed the finding that nest temperatures reached as high as 122F, significantly more than the known lethal limit of 104F.
This graph, from www.co2.earth, shows why eggs are beginning to develop sans incubation: