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For example, if a scientist were to move a chickadee or pigeon egg from one nest to another, would the new bird (second mother) in the new nest incubate or raise the youngling? Or would the new mother reject the egg since it lacks its imprints (like scent for example)?

In other words, can birds differentiate between their offspring and foreign offspring?

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You may not realize, but you actually have two questions here.

Question number 1 is this:

Can birds raise younglings that are not their own?

The answer is yes. We call this Brood parasitism, and it occurs in several species of birds.

There is both intraspecific (between members of the same species) and interspecific (between members of different species) brood parasitism. I believe you want to know about interspecific brood parasitism.

By far the most famous examples are the cuckoos (Family Cuculidae). Some species of cuckoos are obligate parasites, meaning that they only reproduce laying eggs in other birds' nests.

It's very funny (for us, probably not for the host) the fact that sometimes the young parasite is way bigger than the host mum:

enter image description here

A Eurasian reed warbler raising a common cuckoo. Source: Wikipedia

Then, we come to your question number 2, which is different:

If a scientist were to move a chickadee or pigeon egg from one nest to another, would the new bird (second mother) in the new nest incubate or raise the youngling?

The answer here depends on several factors, mainly the species involved.

For species that suffer broad parasitism, there is egg-rejection if the parasite egg is somehow different. If you look at the adaptations to parasitism in the Wikipedia link I shared, you're gonna see that "among specialist avian brood parasites, mimetic eggs are a nearly universal adaptation".

However, species that don't suffer broad parasitism are more prone to accept egg transfer (see @bshane comment here).

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    $\begingroup$ We cannot infer egg-selectivity in most species (as in the second part of this answer) from the observation of mimetic eggs in brood parasites: not all species suffer brood parasitism, and host species have an evolutionary incentive towards egg-rejection that does not exist for species not involved in a host/brood-parasite arms race. Many species will accept egg transfers, and such 'cross-fostering' is widely used in conservation (e.g., jstor.org/stable/3809290?seq=1#page_scan_tab_contents and onlinelibrary.wiley.com/doi/10.1046/j.1523-1739.1993.07010160.x/…). $\endgroup$ – bshane Jun 6 '17 at 1:41
  • $\begingroup$ @bshane Thanks for sharing this, mate. I just edited my answer. Cheers. $\endgroup$ – user24284 Jun 6 '17 at 1:52
  • $\begingroup$ So, in other words, for an inter-specific egg transfer between a non-brood parasitic bird (such as a pigeon) to another, the second mother would probably accept the egg since she lacks any evolutionarily-produced incentive to discern between her own eggs and foreign eggs. But what about if the scientist moved an already hatched youngling to her nest. Would she still accept the transfer? Or can she identify and reject which chicks are not hers? $\endgroup$ – orangebull Jun 7 '17 at 0:18
  • $\begingroup$ @orangebull That's a good question. As this is a different problem, I suggest you post another question: that way, you're gonna attract way more attention. $\endgroup$ – user24284 Jun 7 '17 at 0:26

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