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Most lovebirds can't be sexed based on a visual examination. In fact, the most common type kept as a pet, the peach-faced lovebird, has to be DNA tested to truly determine the sex. Some people argue that female lovebirds are generally smaller than male lovebirds. This is only visible in certain breeds of lovebirds. Some people also assert that a female lovebird's feet are perched wider apart than a male's feet. This has to do with the assumption that a female's pelvis is wider than a male's.This depends on the species. Unlike many other types of birds, most types of lovebird coloring does not differ based on sex. There are some exceptions, however, such as the Madagascar lovebird. The male Madagascar lovebird has grey on its head, while the females are solidly colored green. In general, when lovebirds are interested in mating they tend to shred paper, whether they are male or female. This seems to be true across species, with Fischer's and peach-faced lovebirds, for example, exhibiting the same behavior regardless of sex. While some argue that females are better at paper shredding, and so can be spotted by their skill and precision, this seems to be a difficult way of determining sex. Some suggest that birds that tuck the paper into their tail feathers are likely to be females. If lovebirds are kept in a pair, they tend to form an intense bond. It does not matter what the sex of the birds are. Birds kept together will become a unit. Bonded pairs of the same sex are even known to work on nesting together.
Determine if you have a breed of lovebird that has unique sex characteristics. Do not rely on paper shredding and nest-building behavior to sex your bird. Don't assume that a bonded pair of lovebirds are male and female.