Biologists have found that birds with a short lifespan or a low survival rate lay larger clutches of eggs. The opposite is true as well, longer-lived species or those with a higher survival rate lay fewer eggs. However, the reason why one species of bird may lay one egg and another 10 is more complex. Clutch sizes vary widely, even between related species due to differences in their environment, nutrition and health.

 

"Our results demonstrate not only where bird species live, but how the way they live their lives, specifically their reproduction strategies, has evolved in close association with climate, particularly seasonality," said Jetz of UC San Diego. "Rapid changes to the global geography of climate are likely to impact both aspects and to potentially perturb the long-evolved link between the 'where' of life and the 'way' of life in many species."

 

"In this study," he added, "we answer one of the most basic questions asked about birds: Why do bird species lay different numbers of eggs? The integration of geographic and life history datasets enabled us to simultaneously address the importance of ecological, evolutionary, behavioral and environmental variables in shaping the clutch size of world's birds. We show that increased environmental variation causes birds to lay larger clutches. Most ornithological research has taken place in the highly seasonal environments [a four season climate] of North America and Europe, but most bird species live in less seasonal tropics. Therefore, the small clutch size seen in less-studied tropical birds is the norm, not the exception. Increased predation pressure experienced by open-nesting birds also causes them to lay smaller clutches than cavity-nesting birds, literally having fewer eggs in one basket to spread the risk."

 

Q.  I picked up a bag of seed at a home improvement store during the blizzards last month. But, when I put it in my feeder the birds didn't like it much.  Isn't all bird seed about the same?

 

A.  Yes and no. The seeds themselves are the same; that is white millet is white millet, a black oiler is a black oiler etc.  A seed is a seed regardless of whose mix it is in. 

 

However, mixes vary greatly in the ingredients and proportions.  Some mixes contain high percentages of filler seeds such as milo. Milo was actually developed as a cattle food and was designed to be unattractive to birds. Wheat, rice, buckwheat and grain products are a few more examples of filler seeds that birds generally do not like and do not eat.

 

Black oil sunflower is the most popular single seed that birds eat.  White millet is the second most popular seed, yet it is preferred by fewer than half the number of birds that like black oilers. So any mix that is in majority white millet is out of proportion to the number of birds that eat it. Cleanliness is the other variable in seed. "Field run" black oil sunflower can contain up to 25% debris. A fifty pound bag can have up to 12 1/2 pounds of sticks and stems, so while that is fine, there is just less than one might expect in the bag. Black oil sunflower at Wedel's is 99% clean.