A non breeding plumage Black Tern refers to the alternate plumage that Black Terns acquire outside of the breeding season. The Black Tern (Chlidonias niger) is a small tern species found across North America, Europe, and Asia. During the breeding season, adult Black Terns have a black head, underparts, and wings contrasting with gray upperparts. However, in their non breeding plumage, Black Terns appear quite different.
What does a non breeding plumage Black Tern look like?
In non breeding plumage, adult Black Terns have a white forehead and much more white on the sides of the head. The rest of the head is black but the black does not extend as far down the nape and sides of the neck as it does in breeding plumage. The white forehead contrasts with the black crown. The underparts become predominantly white rather than black, with some variable gray shading especially on the flanks.
The upperparts also differ – instead of gray upperparts, non breeding Black Terns have pale gray upperparts with a fairly uniform appearance. The wings remain largely black but show some gray on the coverts. The tail becomes paler gray rather than blackish-gray. The bill remains black and the legs change from reddish-orange to brownish-gray.
First-year juvenile Black Terns in non breeding plumage resemble non breeding adults but have some differences. Juveniles have a more variable amount of white on the forehead and face, often still showing some black speckling. Their crown may appear dark gray rather than solid black. The white undertail coverts typical of adults may be less extensive in juveniles.
When do Black Terns acquire non breeding plumage?
Black Terns molt into non breeding plumage in late summer or early fall after the breeding season ends. The exact timing varies by individual and region. Some terns start molting as early as July whereas others may still be in breeding plumage in September.
Molt occurs slowly over several weeks. It often begins with the head, breast, and back feathers. Wing feathers are replaced more gradually. Terns migrating long distances tend to replace flight feathers later on wintering grounds. By October, most Black Terns are in full non breeding plumage.
Why do Black Terns have different plumages?
The different breeding and non breeding plumages are likely an evolutionary adaptation related to the Black Tern’s breeding biology and mating behaviors.
During the breeding season, the bold black and gray breeding plumage may help Black Terns identify potential mates and defend nesting territories. The sharp contrast makes their in-flight silhouette easily recognizable.
In non breeding plumage, the plumage differences become less distinct. This likely helps Black Terns blend in more during the non breeding season when they gather in large flocks, often far from nesting areas.
The seasonal plumage change may also be influenced by hormonal shifts related to breeding. Similar patterns are seen in many other bird species.
How long do Black Terns stay in non breeding plumage?
Black Terns remain in non breeding plumage through the fall and winter months. They start to regain breeding plumage in late winter and early spring in preparation for returning to breeding grounds.
The molt back into breeding plumage again starts with the head and underparts. It proceeds through spring as birds migrate back to nesting sites. Not all individuals attain full breeding plumage at the same time.
By May or June, most terns on breeding grounds are back in silky black breeding plumage. But some incoming migrants may still be transitioning. Juveniles acquiring breeding plumage for the first time often attain it a bit later as well.
Do both males and females get non breeding plumage?
Yes, both male and female Black Terns acquire non breeding plumage. The sexes look nearly identical in this alternate plumage outside of the breeding season.
During breeding, males and females can be distinguished by small differences. Males tend to have a slightly darker gray mantle while brooding females often show some faint gray feathering on the undertail coverts.
But in non breeding plumage, these subtle differences disappear. Both sexes take on the same white forehead, pale gray upperparts, and white underparts.
Can Black Terns in non breeding plumage still breed?
It is possible but unlikely for Black Terns to attempt breeding while still in non breeding plumage. Terns typically gain breeding plumage in time for the nesting season.
However, in some cases late spring cold snaps or food shortages may delay nesting efforts. This could potentially overlap with the tail end of molting into breeding attire.
Out-of-sync breeding attempts are not common. And terns in transitional plumage tend to be less successful mating and defending territories.
Do other tern species have non breeding plumages?
Many tern species have distinct breeding and non breeding plumages like the Black Tern. The differences are especially pronounced in the marsh terns of the genus Chlidonias.
For example, White-winged Black Terns and Whiskered Terns show marked seasonal changes. Most other marsh terns exhibit more modest variations in non breeding plumage as well.
Some tern species show essentially no changes between seasons. Common Terns, Arctic Terns, and Forster’s Terns look fundamentally the same year-round.
In these species, non breeding birds simply appear a bit faded or disheveled due to wear and molting. But there is no wholesale plumage change.
Do juveniles develop non breeding plumage?
Yes, juvenile Black Terns molt from their distinct first-year plumage into a non breeding-type plumage by late fall. This juvenile non breeding plumage is slightly different than adults but serves a similar purpose.
Young terns hatch in a downy plumage. After fledging, they acquire a juvenile plumage that has some black markings but is overall grayer than adults with lots of white speckling on the back.
Starting in late summer and fall, juveniles go through a partial molt. They replace many body feathers and some wing coverts with a plumage resembling adult non breeding colors.
This provides camouflage and reduces differences when young birds join non breeding flocks. Juveniles do still usually retain some juvenile wing feathers through the winter.
Conclusion
In summary, the non breeding plumage of Black Terns provides more cryptic, less conspicuous coloration suited to the post-nesting season when terns congregate in mixed flocks. The seasonal shift likely serves both camouflage and social signaling purposes.
Both sexes and all ages transition between breeding and non breeding appearance in this species. The patterns showcase the remarkable flexibility that allows birds to adapt their plumages to changing environmental and life history needs.