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Answer:
Jeff,
Since the average clutch size of a Canada goose is 4-6 eggs, you ask a very good question in, “Where do these other goslings come from and why?”
The quick and dirty (and cumbersome) answer to your question is what biologists refer to as “posthatch brood amalgamation.” Several additional terms that roll off the tongue a bit easier include adoption, creche or mixed brood, gang-brooding and kidnapping. Post brood amalgamation is not restricted solely to Canada geese, and has actually been documented in at least 41 waterfowl species.
In adoption, a single female or pair will accept additional young as their own. In mixed and gang broods, parents from separate broods will join and raise their young as a combined effort. Kidnapping refers to a female or mated pair that will aggressively kidnap young of another brood.
So far, we have answered where the extra goslings come from. Now we need to answer why this behavior occurs. Here are a few possible reasons:
- Larger broods may reduce the risk of predation…more goslings means more eyes!
- Host offspring might experience increased survival if adopted or kidnapped young are displaced to the perimeter of the brood.
- A female who leaves brood rearing to another individual or pair is able to spend her time feeding, and can therefore recoup her depleted energy reserves more quickly.
- When food resources are scarce, larger broods tend to displace smaller broods from feeding areas.
While it does occur, post brood amalgamation occurs infrequently in Canada geese. If you remember from a past answer, both male and female Canada geese participate in brood rearing. As a result, the increased parental care helps maintain family groups.
Thanks for the great question.
Sincerely,
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