Answer: Yes and... No
A discussion of whether birds mate for life has to begin by having an understanding of what we mean by the term "mating for life".Specifically, as it refers to birds.
Some people feel having a mate for life means, marriage for 50 - 60 years, the partner passes, and surviving mate lives with fond memories until their passing.
If mating for life means one partner in a lifetime to you, then few birds fit into this category.
However, one that sometimes falls into this category is the Canada Goose. They form lifelong pairs and may never mate again after one dies.
Then again, some songbirds will find new mates in the same nesting season.
Others will forage for food through the breeding season joining flocks in the fall.
Then others will help feed and raise the young of other pairs, but all will attempt to find a new mate at some time.
Most of our North American birds do not mate for life. Rather, most pair bonds are formed for a single season.
Those birds that pair for a season can be monogamous for the season or polygamous breeding with multiple mates.
Monogamy is one male bird with one female bird through a single nesting cycle.
The pair may stay together raising a single brood and then change partners for a second brood in the same season. Still, they are considered monogamous.
Other pair bonds may be formed and last over several seasons choosing to re-nest with the previous mate. Doves, Robins, and others are on this list.
Oftentimes, these birds are considered as meeting the definition of "birds mate for life".
Technically not accurate since they don't stay together throughout the year. And may or may not re-pair.
We do not refer to faithfulness when we speak of birds and monogamy.
First-year mortality rates are very high for our small songbirds and reproduction is a primary goal.
The truth is, DNA evidence points to a high percentage of promiscuity.
Many females lay clutches that have been determined to be from different males.
This in turn suggests males may breed with more than one female even though a pair bond may have already been established.
Some of our common birds breed with different mates but only tend to their first mate's nestlings.
Several larger birds closer fit the definition of, "mating for life". Among them are swans, geese, eagles, and some owls.
Why birds mate for life is not as romantic as one may think.
When you factor in the time needed to migrate, establish territories, incubate, and raise young, you'll realize that the time and energy needed to attract a mate would minimize reproductive time.
The Bald Eagle as an example spends just over a month incubating the eggs and 2 1/2 to 3 months raising their young in the nest.
Establishing lifelong pair bonds works to their advantage.
I suppose the question of whether a bird mates for life comes from wondering what will happen should one of the two die.
Many people fear that birds mourn the loss of their mate, and will never mate again.
I can't say whether birds actually experience loss or whether what we interpret as mourning is just confusion.
I do know most of our small wild birds will always attempt to find new mates. That is nature.
Whether a bird mates for a single brood, 40 years, or for life, we should provide the best environment for them to be successful at what they're attempting to do, raise more birds.
Where Birds Sleep