On a sunny morning in late April, Lama Zopa Rinpoche was looking out through his dining room window and saw a red-tailed hawk gliding low over the hill. "It's looking for birds," he said. An attendant mentioned to Rinpoche that he often had the wish to chase the hawks away when he saw them hunting but was concerned that by doing so he would be depriving the hawks of their food. Rinpoche replied to his comment as follows:

If you protect one bird from the hawk you protect the hawk from hundreds of thousands of eons of creating negative karma and experiencing birth in the lower realms. Negative karma can result in suffering. One karma leads to many negative karmas and hundreds of thousands of eons of lower births, because karma is expandable. Even birth in the human realm is a cause to experience the three sufferings of aging, sickness, and death.
All actions have a result. When you harm, you receive harm back. With the experience being similar to the cause, you harm again, and so you receive again the four suffering results and birth in the lower realms. And so it goes on and on like this with no end.
By chasing the hawk away from a bird, the bird gets so much happiness for many lifetimes and freedom from the four suffering results and endless suffering. In addition, the bird gets saved. You cause it long life and protect it from death.
Rinpoche went on to explain how to offer food to birds and other animals in the best way.
When we give food to birds we should chant the Mitrugpa, Medicine Buddha, Chenrezig and Five Powerful Mantras and then blow over the food. Giving food to birds protects them from hunger and thirst. The most important benefit is that it purifies negative karma and defilements. It helps them to not be born in the lower realms, by purifying them. It blesses their minds. By giving food in this way, it becomes a practice of loving kindness, of giving material things, and of giving fearlessness and purifying negative karma. There is so much suffering and fear in the lower realms and this is a way to protect them from it.
There are different types of charity. There is charity of materials, charity of loving-kindness, charity of Dharma, and charity of fearlessness. Benefiting sentient beings is a samaya of Vairocana. When you take Highest Tantra Yoga initiation you take the vows of the Five Buddhas.
The attendant mentioned that at a nearby Dharma center there were many bird feeders. At one feeder was a small box which plays the mantra of Chenrezig for the birds to hear as they eat. When the food is gone and the batteries have run low, the birds sit on the fence near the feeder and wait patiently for someone to come and fill the feeder, and, presumably, to change the batteries in the mantra machine. Rinpoche continued:
Feeding the birds and the other animals doesn't have to be done for one's own pleasure but can instead be a sincere practice of giving. The paramita of charity is the Ratnasambhava samaya in Highest Yoga Tantra and is also part of the three times morality samaya of Vairocana - integrating virtue.
You are offering fearlessness by saying mantras and then blowing on the food or water. This is morality working for sentient beings - giving sentient beings what they need. Giving food and water is material generosity. When the mantras are said and blown upon the food and water it becomes the charity of fearlessness, and when you play the mantras so that the animals can hear them it becomes the charity of Dharma.