my lovebirds

Question
QUESTION: i have three lovebirds, we know one is a male and one is a female but we are not sure of the sex of the other one, I tried to put my female with this other bird but she tried to attack it, so then I tried to stick my male bird with this other bird and they are fine together, but they are not trying to mate, this other bird that we are not sure about has never layed an egg and we have had it for a year, but when I put the nesting box in the cage with it it stays in there and is very protective of it, if this bird is a male why would my female lovebird try and attack it. If it is a female then why hasn't it layed any eggs, could something be wrong with the bird?, this lovebird also does a lot of knocking on the sides of the nesting box I heard that the males are the ones that do this.Do you think I should just go ahead and get a DNA kit for this bird?
ANSWER: Hello I reccomend in your case DNAing all three. THe one that attacked the other could be a hen...both could be hens and they offen dont get along. Also not all lovebirds adore each other even males/females I have 6 handfed peachfaced lovebirds two lutinos one normal green, one fallow/grey one pastel colored pied and one whtie faced tucriwise and the three brighter colored lovebirds HATE the pastel colored lovebirs with a passion like no other...I was indeed told it was because they are odder colors. Two females  will go to enst they of course cant have fertile eggs but you'll know you've two hens alying when you get 10+ eggs in the nesting box also two males wil assume the roles of male/female you'll know because there are no eggs.

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QUESTION: thank you for your response, well I don't really need to test all three, as I said we know for sure that one is female and one is male for they have had a baby together, but i think that the male is old for they have only ever produced 1 baby together out of about 4 batches of eggs.but the baby later hurt itself and died. It is this other bird that we have had for a year that we are not sure about, it is a white face lovebird the other two are male lutino and female peach face.They produced one baby lutino. Anyhow thank you again for your response, I think i will just do a dna test on this newer bird.

Answer
Hello...so sorry i must have missed that part...my bad I just had some many emails to anwser and I was in teh middle of building a flight cage for my 6 peach faced lovebirds one normal and 5 mutation...I too have a whitefaced he is so cute lol and two lutinos lol plus a pied and a fallow/slate type color I know to have one male because he mates with things the other are all too young at this time I have just finished the flight cage and now they will live together and pair off so I have no reason to DNA sex the little buggers ;). It may not be because he is old males are fertile until basicly death with everything animal I've ever had its the females that can go infertile but with birds I am really not too sure of what age thou I don't reccomend breeding females beyond 5 or 6 years of age for there health's sake. I can offer some advice on sexing the whitefaced lovie....take notice to how far it keeps its legs when perched most of the time take note to if it has a square or narrow tail.... I notice with my male bird he sits with his feet very close together and has a narrow straight pointing tail weathers the fallow/slate baby sits with its legs farther apart has a square tail also which appers shorter I belive to have three hens and three males because of there looks so far but really I know only for sure I have one male It will be a few more months until I can tell by behaviers. Also with every type of bird I've ever owned I've noted females bite Much harder then males do I've noted this with budgies and cockatiels anda few of my lovebirds are nippier then others and the are the ones I'm already assuming female. So have a look at these behaviers before DNAing it will save you money and spare the birds feathers lol. Also if given paper tissue(unscented and uncolored) or tolite paper/printing paper females will shred it and stick it under there wing feathers supposibly if they are sexually mature that is(6-10 months old). Best of luck with your breeding adventures and I am sorry to hear you lost your only baby that was produced...babies can be clumbsy with toys/cage accessories and have to be provided with things that are very safe...weathers a baby bird might get caught in a toy an older bird wont play with it the same way or for such a long time to cause it to become caught ect ect. If you need help with anything else feel free to ask.