Rabbits are probably the culprits that have bitten off the tulip plants. They prefer the succulent foliage of tulips, lilies, and others in spring. You could tell your neighbor to consider planting daffodils this fall; rabbits leave that foliage alone since it is poisonous.
The definitive test for rabbit damage is the 45-degree angle cut of the stem. Look carefully for that sharp-angled cut.
Online Resources:
Cottontail Rabbit Control