Please use below spec to train.
It runs with resnet18 backbone, bs4 and totally 120 epochs.Train_bird.txt (3.1 KB)
It can fix your issue.
When it runs at 30th epoch, the mAP is already 85%.
In the end, the training result is 92.9396%.
Epoch 120/120
Validation cost: 0.000202
Mean average_precision (in %): 92.9396class name average precision (in %)
bird 92.9396