Cowbird Brood Parasitism
The nesting season 2015 on the Jonesboro Bluebird Trail has known several cases of Brown-headed Cowbird (BHCO) brood parasitism. I have recorded 2 Carolina Wrens (CARW) and 3 Bluebird parasitized nests as follows:
- Box 310: CARW nest with 5 eggs of her own and 1 BHCO egg, but the CARW abandoned the nest almost immediately.
- Box 5: Bluebird nest with 4 eggs and 2 BHCO eggs. Both BHCO eggs hatched (but one died within 2 days), whereas only 2 of the 4 bluebird eggs hatched. On day 8 (day 10 for the BHCO), the BHCO chick tried to fly out of the nest box but only succeeded in hopping in the grass. I put it back in the box. Unfortunately, a snake got into the nest box between by day 10.
- Box 9: CARW nest with 5 eggs of her own and 2 BHCO eggs. Again, the nest was abandoned.
- Box 121: Bluebird nest with 4 eggs plus 1 BHCO egg. The BHCO egg hatched as well as 3 of the 4 bluebird eggs although only one bluebird chick survived. The BHCO was gone by day 11. The remaining bluebird chick likely fledged.
- Box 122: Bluebird nest with 4 eggs and 1 BHCO egg. The BHCO and 2 bluebird eggs hatched and successfully fledged.
Conclusion: No luck for BHCO with CARW, but not complete failure with bluebirds. Maybe CARW recognize foreign eggs better than bluebirds.
