There’s a headline grabbing title if ever one was needed!
The eagle eyed among you have been in touch to ask a fantastic question about a point made on Winterwatch… That only chequer pigeons breed in winter.
Many have asked if pigeons prefer mating partners that look different from themselves, how does any winter breeding happen at all?
In winter, won’t the non-chequered partner be in non-breeding condition?
The truth of the matter is down to something called ‘gonadal regression’. Most temporal breeding birds breed seasonally in order that there is lots of food available for their nestlings. In order to be ready to breed at the right time, such birds use day length (known as photoperiod) as an indicator to make sure their bodies are ready for reproduction at the correct time. This is why it is common to hear of some seasonally breeding animals breeding too soon, when spring comes ‘late’. Day length tells them it is time to breed, despite a ‘late’ spring occurring.
But what about pigeons? I hear you ask.
Pigeons have an extra problem to overcome – the production of ‘pigeon milk’. Pigeon milk is produced by BOTH male and female pigeons and is regulated by a hormone called prolactin. In order that both male and female pigeon produce pigeon milk at the correct time (when the young hatch), each pigeon’s own hormone production has to be influenced by the other bird. In that way, they can synchronise their hormones.
Female pigeons are heavily influenced by the behaviour of their mate – if the male pigeon of the pair is ready to reproduce, his courtship behaviour helps to stimulate the female to be in the same mood.
Here we see a male pigeon cooing to his mate
So what about the gonads?
In winter, as the days get shorter, BLUE BAR male pigeons recognise this and their testes begin to shrink – this is known as gonadal regression. This shrinking reduces their circulating testosterone levels and stops the pair reproducing. As an upside, these males are then free to develop fat reserves to help them survive the cold months of winter.
CHEQUER birds on the other hand are not as influenced by changing day length; their testes remain large and continue to produce lots of testosterone in the depths of winter. As such, these virile males are able to continue to stimulate their female partners into reproducing. This comes at a cost though; these males are unable to lay down fat reserves – however, in our busy cities there is usually so much food to eat that this does not cause them any problem.
Therefore, despite a pair only having one male chequer individual, the pair can still breed in winter, when those with a blue bar male will generally not.
My current results show chequer males are the most common plumage type – a true sign that pigeons have evolved to take advantage of our wasteful lifestyle.