With longer days comes different, sometimes aggressive, bird behavior

sunnews.comMarch 11, 2014 

Northern mockingbirds becoming highly territorial is a sure sign of spring.

BY GARY PHILLIPS — For The Sun News

With the onset of spring-like weather and the lengthening of daylight hours, seasonal changes are becoming evident all around us.

Native red maples (Acer rubrum) have been in bloom for a few weeks now, and native Carolina laurel-cherry (Prunus caroliniana) are also flowering. Many deciduous plants are sprouting new growth, and some insect species are emerging.

Spring is a time of change, and in addition to changes of plants and insects in evidence, many other animals are exhibiting their own seasonal awakenings, and those of the birds are perhaps the most easily observed.

Invariably, there are some bird behavioral changes, usually most notable in mockingbirds, bluebirds and cardinals that become a cause for distress in some folks.

Bird behavior is under hormonal control. When to migrate north or south; when to start the breeding season; when to fatten up for migratory treks or to survive winter are all influenced by the amount of light in a day, known as photoperiod.

Birds have special light receptors on their skulls known as photoreceptors that sense the length of light in a day. In spring, as photoperiod increases, these receptors send signals to the brain which in turn stimulates the production of hormones. Once the breeding season has finished for birds in late summer, the decreasing photoperiod causes a concurrent decrease in hormone production, which causes behavioral and physiological changes in our feathered friends.

In fact, the reproductive organs of birds actually shrink to a fraction of their breeding season size for the winter, as they will not be necessary until the next breeding cycle. In spring, the increased hormone production leads to an increase in size of those organs as they become functional once again in order for the birds to complete their annual life cycle.

Along with the increased testosterone production in males comes an increase in aggressive behavior as they seek to define and defend territories in order to attract mates and protect resources that will be necessary to successfully raise offspring.

Northern mockingbirds often provide what some may view as extreme examples of territorial behavior, sometimes seeking to chase any other birds from feeders in an area they seek to claim as their territory. Many times this extreme behavior is a result of either a particular food item (e.g. suet, fruits/berries, nut meats, etc.) or a coveted breeding spot (e.g. a particular shrub, small tree, etc.)

Mr. Mockingbird is not being “mean,” he literally can’t help himself. He’s merely being the best mockingbird he can be.

Reach GARY PHILLIPS at 248-4595 or carolinensis@yahoo.co

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