Why do they leave Brazil once a year??

[barry resvick]

Hi friends!
By this time most of you folks down south are well into your Martin seasons, but have you ever wondered why they ever leave their homes in Brazil to come up here to nest? I have been trying to get an answere to that question for years now. I read an article that said that Brazil has their winter when we have our summer but if you check their temperatures they are rarely below the 70s, so why would they come all that way when their home temperatures are very warm?? Could it be all the free accommodations?
Any input would be very welcome

Sincerely
Barry and Wendy resvick

[Evan337]

Hi friends!
By this time most of you folks down south are well into your Martin seasons, but have you ever wondered why they ever leave their homes in Brazil to come up here to nest? I have been trying to get an answere to that question for years now. I read an article that said that Brazil has their winter when we have our summer but if you check their temperatures they are rarely below the 70s, so why would they come all that way when their home temperatures are very warm?? Could it be all the free accommodations?
Any input would be very welcome

Sincerely
Barry and Wendy resvick

It is certainly related to the Earth's orientation to the sun. As you mentioned, the southern hemisphere is experiencing their summer season when we are experiencing our winter season. Martins feed on flying insects. Flying insects are most prevalent in warmer months. Even though parts of South America closer to the equator may have milder winter temperatures the time between sunrise and sunset will be shorter in the southern hemisphere right now than it is in the northern hemisphere because of the earth's orientation to the sun. Longer daylight hours for martins translates into longer feeding hours so I would think more hours of daylight plays a role as well. I have read where martins are very sensitive to the Summer and Winter Solstices. Once the Earth shifts its orientation to the sun migration begins.

I have often wondered if some of the older martins decide to just hangout in south Florida or south Texas/ Mexico to avoid the long trip back to south America but I imagine most get south of the equator for the northern hemisphere's winter months.

[Emil Pampell-Tx]

Martins go to many different countries during the winter. The coldest days in Argentina are in July, with avg temps of 54 deg. Even though it may not be as cold as we are, I am guessing that there may be a lot less food for the martins to feed on during the cooler months in South America

[Forum Admin]

If all the estimated 4 million-8 million Purple Martins stayed in Brazil, there would not be enough cavities for nesting, or food for young.

[barry resvick]

Thanks so much for all your input on this subject because it's always intrigued me as to why they would leave the beautiful rain forests of south america

[Emil Pampell-Tx]

Barry, the martins and most other birds time their hatch of babies when there are maximum bugs, and they go to areas where there are maximum bugs. Rain forests in Brazil may be beautiful but it may be difficult for the martins to catch those bugs, since martins like to feed over open fields and streams. Even here in the United States, martins do not like housing in the middle of a forest or on the very edge of a huge forest..Since many of the forests are being cleared for cattle ranching, I wonder if some martins may not stay there thru the winter

[Ed Svetich-WI]

The opposite question is also relevant. Why do martins and many other bird species leave North America once a year? It has been hypothesized that avian migration originated in the nearctic regions of the globe to the neotropics. 50% of resident bird species in neotropic areas have ancestors in the nearctic regions. Many species migrated, liked what they found, evolved and stayed in South America. Most migration moves from a location of want to a location of abundance. Abundance can be defined as food or breeding sites.

Migration to neotropic areas in the fall involves a much greater number of birds of a given species than those that migrated north a few short months earlier. In my case, 48 (24 pair) returning purple martins produced 130 fledglings in 2015, roughly 2.5 times the number arriving in the spring. Coincidentally as summer wanes, sunlight is diminishing and the pineal gland receptors take note with the resultant decrease in hormones, temperatures are cooling, the previously abundant food sources are less so. With many more mouths to feed, as well as other factors, the movement is to the south where abundance still predominates.

Fast forward to early spring here in North America and the birds feel that urge. Although the avian population that began the southward migration has now been diminished by the deaths of many birds due to various factors, there are far too few nesting sites to accomodate both the resident neotropic population and the transient nearctic birds.

The move is now toward the abundance in the north. There is an abundance of vacant nesting sites. The insect population is growing and will soon boom as the weather warms, hopefully peaking as young are growing. Site fidelity now comes in to play.

Nature is fascinating.

Ed