Birdseed can go bad if it is improperly stored or allowed to rot in poor conditions, and the bugs, mold and bacteria in spoiled seed can cause diseases among feeder birds. Always check to be sure seed is dry and fresh without strong or sharp odors, and change seed after feeders have gotten soaked to keep the seed from spoiling.
While a very small amount of bread may be acceptable to feed birds, large quantities are poor, unhealthy food with little nutritional value. If you want to augment your feeding station with bread, opt for healthy bread such as whole grain varieties, and make a “sandwich” that includes peanut butter, suet, seed and other appropriate foods instead of offering plain bread.
Nectar for hummingbirds and orioles is easy and quick to make, so there is no excuse for not using fresh nectar. Old nectar looks cloudy or discolored and may show floating particles. When spoiled, nectar can harbor mold and bacteria that is fatal to birds, so it is best to refresh nectar every few days, cleaning the feeders simultaneously to avoid contamination by old residue.
Do not offer birds any fruit or seed that has been treated with pesticides, herbicides or other potentially toxic chemicals. Even small quantities of these chemicals can be fatal to birds, and poisons may build up in birds' bodies to cause breeding problems or be passed along to young birds. If the fruit you want to offer birds is questionable, wash it before adding it to feeders, or opt for growing your own produce for birds.
Junk food such as chips, cheese puffs, corn chips and other foods are all bad for birds. They offer very little nutritional value and are filled with processed chemicals that have not been tested on birds, so their effects cannot be predicted. If you want to offer a unique treat instead, offer plain, air-popped popcorn with no salt or other toppings.
Many birds are carnivorous, but avoid offering raw meat in any form, including ground meats or meat scraps. These foods can spoil very quickly and will grow dangerous bacteria that can kill birds, and they may also attract other undesirable feeder pests such as rodents. Instead, offer fatty protein as suet to give birds a nutritious and safe option.
Scraps of cookies, donuts, cakes and other sweet baked goods may seem perfect for birds, but just like other junk food, they do not offer good nutrition and are packed with processed ingredients that are not suitable for birds. Instead, make bird “cookies” from suet, cornmeal, peanut butter and other healthy foods.
Honey is a natural sweetener, but it is not good for birds. Even the best quality honey can harbor bacteria and grow mold that can be fatal to backyard birds. Avoid using honey to make hummingbird nectar or oriole nectar and do not include it in any suet cake recipes.
Foods high in salt are not good for humans, and the same is true for birds. While birds can process small amounts of salt without difficulty, large quantities are dangerous. Avoid offering birds any foods high in salt, such as salty meats, chips or other animal foods that include salt for nutritional value.
Unlike mammals, birds are largely lactose intolerant and cannot ingest large quantities of milk. Like salt, they can tolerate small quantities, but foods high in milk are poor food choices. Avoid offering birds any soft cheeses or milk directly, and instead concentrate on healthier diet choices.