In our latitudes, most animals reproduce in the season of greatest resource abundance. Thus ensures that the offspring when they are born with enough food to grow and develop. But within the same species, there may be differences between individuals in the onset of reproduction that can sometimes be several months within the same breeding season.
These phenological differences in birds usually due to two main causes, especially in long-lived species and mainly monogamous. First, older individuals are often the dominant and so are the first to refine the best places to play, while young and inexperienced have to wait for free places are usually those of poorer quality, before starting playback. Second, those partners who have already played in previous years will not have to spend time searching for another individual of the opposite sex and spend less time courting stage, so that lay eggs earlier.
In some species of seabirds such as shag, these differences can be as high as four or five months. In the western population of Asturias where we worked for years is not uncommon in the month of April has partners with large chicks fully feathered, with other couples that are still incubating.
In the previous video, taken two weeks ago can see a nest with two chicks fully feathered about to leave the nest, although they are still fed by parents. Meanwhile, a short distance from the nest were two other nests, one that still contained 3 eggs and other chickens medium.
These differences in laying date have important implications for chickens, as has been shown to shag chicks leave the nest before they are dominant when they arrive at the nursery where they are concentrated ( Ensuring, 2000). This implies that dominance status may choose the best sites will less risk of predation and being swept away by waves during storm surges.
NOTE: If you are interested in the issue of shags and the study we are doing for years, the next 12th May at 22:00 in the program The Sea of \u200b\u200bRTPA Asturias, a small issue story on our work. References
Ensuring , A. (2000). The Importance of hatching date for dominance in young shags Animal Behaviour, 60 (2), 181-185 DOI: 10.1006/anbe.2000.1445
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