Q Do the nutritional needs of birds vary with the season?

A Yes. Spring is a good example. Energy needs increase. Some male birds are expending energy by molting into courtship plumage. They also burn calories with extended singing and other courtship behaviors, and with territorial defense. If you feed the birds, the change from cold winter weather to warmer spring weather is no reason to stop. The food you provide can be put to good use by your guests.

Breathing easy Q Do bird embryos need to breathe? If so, how can they do it from inside the egg?

A The egg, a self-contained womb, so to speak, is porous. It allows exchange of air and water vapor with the outside world. Without this capability, the chick within the egg would suffocate.

Egg timing Q If a bird lays more than one egg, how often is an egg laid?

A It takes about 20 hours for an egg to be created by the female. She lays one egg per day until her clutch is complete. Most often, the egg is laid in the morning. This means the bird does not have to carry the weight of the egg during the day when it is feeding and flying.

Anatomically correct? Q Do male birds have testicles?

A Of course, but not that you would notice. A male bird's testes are small, and really small during its nonbreeding periods. The testes shrink to help reduce body mass. This means less weight to carry when flying. Come spring, however, the testes will enlarge in size as much as several hundredfold to provide the needed sperm.

Droppings Q Do birds urinate?

A Not exactly. That white paste that birds deposit on your car, the stuff that's so difficult to remove, is a combination of urine and solid waste. Birds, with the exception of the ostrich and the rhea, do not have bladders, which lightens the flight load.

Hatching help? Q How does a chick get out of the egg? Do parent birds help?

A No help is given or needed. The chick develops what is called an egg tooth before hatching. This sharp pointed "tooth" is at the tip of its upper beak. It uses this tool to rasp and weaken the shell. The chick also has an extra-strong muscle in its neck to help it push against the shell when hatching time comes.

Jim Williams can be reached at two-jays@att.net. Join his conversation about birds at www.startribune.com/blogs/wingnut.