THE ANIMAL FILES

Moor frog

Rana arvalis

A male’s blue breeding colour is a brief appearance, not its year-round coat.

Moor frogs are opportunistic predators of small terrestrial invertebrates. During peak breeding, males can turn conspicuously blue for only a few days, while females remain brown. Shallow spawning water connects this brief display to the next generation.[1]

Follow the evidence ↓
Moor frog
Image: Charles J. Sharp · Commons · CC BY-SA 4.0
Male colour
Briefly blue during breeding[1]
Food
Beetles and other invertebrates[1]
Spawn
Clusters in shallow water[1]

A few blue days

Blue colour occurs during peak male reproductive activity, not throughout the year. Reflectance changes also extend beyond what human eyes see. Studies discuss possible signalling functions, but brightness should not be treated as a fully proven universal measure of mate quality. A photograph captures one stage of a seasonal change.[1]

Waiting for moving food

Frogs often wait for prey rather than searching continuously. Beetles are frequent foods, with flies, other insects, slugs and spiders also taken. Larger frogs tend to take larger prey. Movement and body size therefore affect what enters the diet, without requiring conscious selection of the nutritionally best item.[1]

A concentrated breeding period

Males form calling choruses after winter dormancy. Spawn is placed in clusters in warm shallow water, and breeding can be completed over a short local period. That concentration makes a blue male especially noticeable in season but easy to miss at other times. Local conditions matter more than a universal calendar date.[1]

A COMMON MIX-UP

Are blue males blue all year?

No. The conspicuous colour lasts only briefly around peak breeding.[1]

TRY A LITTLE REASONING

Why would a survey outside breeding fail to record blue frogs even where the species lives?

Reveal the explanation

The colour is seasonal and short-lived, so absence of blue does not demonstrate absence of the species.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Rana arvalis (adapted and translated; exact revision)
  2. NCBI Taxonomy — Rana arvalis (identity and game lineage)

Last fact check:

One discovery leads to another

Common frogOne pond, two very different menus.Rana temporaria ↗American bullfrogA pond chorus is a moving social scene.Aquarana catesbeiana ↗Marsh frogThe tadpole’s menu is not the adult frog’s menu.Pelophylax ridibundus ↗