What’s up with this weather?

We have been in the grip of a prolonged vortex of cold air from our northern neighbors since February 4 with daytime highs in the negative digits (F) and nighttime lows dipping well below -10 F (e.g. last night was -21 F). Just for something to inspire me mentally (?), I added up the last 10 nights of low temperatures and came up with a grand total sum of -95 degrees. Now that’s arctic! Needless to say it’s difficult for my fingers to work camera buttons at these temperatures, let alone get outdoors for a walk in the backyard.

But, in the spirit of Valentine’s Day and to commemorate a time when I was braver about venturing out in -15F weather, here are a few photos of the Trumpeter Swans on the Mississippi River at Monticello, MN, engaging in courtship displays to cement their pair bond — love is in the air for these swans, most of which mate for life.

Even in the warmth of a beautiful sunrise, this landscape looks unforgivingly cold. And it was about -12F on February 9, 2014,
Trumpeter Swans pair up about the age of 3 or 4 years. Each year, there is a lot of “conversation” between members of the pair as they go about their ritual of preparing for the next breeding season.
Head bowing is an important part of the ritual — always done in synchrony.
The iconic heart-shape formed by the arches of their necks as they face each other during a part of the courtship ritual. This shot is always a popular Valentine’s Day image.
The swan pair stay together all year long. In the winter they spend the night on the water, then fly off together in the morning to forage in fields where there might be some left over grain. They will remain together, rearing a clutch of 2-5 or even 6 goslings each year, until one or both of them die — some as long as 25 years.
Some males that have lost their mates never find another female to form a new pair bond with and remain bachelors the rest of their lives. Hiking along a creek on a cold February day in 2016, I found one lone swan accompanied only by Mallards.

Thinking of warmer days ahead, I wish you a Happy Valentine’s Day, 2021.

why are cardinals so red? — continued

The proximate (immediate) answer to the question of why cardinals are red is that they have a diet rich in carotenoid pigments (e.g., the pigment that makes carrots orange), and will incorporate those pigments into their feathers as they develop each year during feather molt.  To read more about this process, click here to read an article from Bird Watching Daily that explains where feather colors come from.

northern cardinal

Resident Cardinal male posing on a garden stake in the backyard.  He’s bright and he’s loud, and he makes sure his mate and all the other would-be holders of his territory know it.

But I’m interested in the evolutionary basis for why cardinals stand out among other species residing year-round in northern climates in retaining their bright red coloration instead of molting to more muted shades during the non-breeding season, like, for example American Goldfinches do.   Cardinals undergo a post-breeding feather molt, just like other species, so why risk attracting predators with bright red, when you might escape notice with a dull brown plumage instead?

summer vs winter American Goldfinch plumage

Summer (top) vs winter (bottom) American Goldfinch plumage

Does sexual selection (that is, female choice for the most beautiful male, as Richard Prum argues) play a role?  Please see the yesterday’s Back Yard Biology post for more information about the importance of beauty in female choice.)

Some additional facts regarding male-female relationships in Cardinals and their close relatives, the Pyrrhuloxias of the southwestern U.S., might help to answer the question.

Cardinal vs Pyrrhuloxia--DFW Urban Wildlife

A comparison of two closely related Cardinal species, the Pyrrhuloxia, Cardinalis sinuatus (1 and 2) and the Northern Cardinal, Cardinalis cardinalis (3 and 4). Illustration in Chris Jackson’s DFW Urban Wildlife blog.

The first thing you notice from the illustration above is that the Pyrrhuloxia male and female look more alike than Northern Cardinal male and his mate do.  Why might that difference have arisen in such closely related species? And does it have anything to do with female choice for brightly colored, beautiful males?

The second and interesting difference between the two species is that Pyrrhuloxia share a pair bond only during the breeding season, breaking up in the non-breeding season into loose, often mixed-species flocks of seed-eating birds that move around to find food in their dry, desert habitat.  Each year, males vie for available females by staking out and advertising their territories, often very aggressively.  In contrast, Northern Cardinals may maintain their pair bond year-round, often for multiple years, unless one of the pair dies, and the pair stays in the same general area in which they nested, year-round.

cardinal courtship feeding-rudiger merz

A year-round pair bond exists in Northern Cardinal mates, which renews its strength in the spring with courtship feeding.  (Photo by Rudiger Merz)

Female Cardinals are making a choice of more than just a breeding partner; they may be choosing a life partner and his residence (territory).  Richard Prum might argue: what’s a male to do, but be the most beautiful thing she has ever seen?  And if he is better looking than his neighbors, she stays with him through that year and the next.  They raise multiple broods of young Cardinals together, and he passes on his good looks to the next generations.


This is an amazing high definition video of male and female Cardinals feeding their chicks (by FrontYardVideo).

In other words, it’s possible that their long-term pair bond and high fidelity to a territory year-round makes it possible for choosy female Cardinals to drive the accentuation of  beauty (in this case, “redness”) in their male partners, to the extreme that male Cardinals never lose their red color during the year.