What day is your bird on exactly?
It happens frequently, their are thoughts your bird needs a certain prerequisite stat before it'll be added to the list.
Some people don't get even the deliver packages til 60s, yet my bird had it halfway through adolescent. The people who had to wait til 60 days were intelligent bird,s whereas mine was a juiced up str bird, 3 vomp carrots a day, constant training, etc etc
It's hard to confirm since it seems to happen rarely, may be a glitch.
Either way, it doesn't matter if your training your bird for str/end. Stick to deliver packages until it's endurance is capped.
If your focusing on intelligence stats though, well I dunno what to say D: