By Sam Vaughn, DVM, Dip., ABVP—Avian Practice
We in the Midwest have noticed an increase in the number of eggs since the drought has passed. Do you know why the drought severely affected egg production, even though our birds are kept in artificial environments?
Your question and comment have been very common this year. The drought has certainly affected production, and I am not sure of all of the intricacies involved. However, we suspect that an effect from humidity and barometric pressure are to blame. The lack of humidity, I believe, certainly reduces breeding behavior. However, as you mentioned, most of our birds are in artificial environments and humidity is controlled by bathing or more elaborate environmental manipulations.
Barometric pressure has long been known to affect animal behavior and activity. I recall an old saying by my grandfather that game and fish were always on the move when the barometer was falling. This seems to still hold true today, although I cannot explain exactly why it is so.
I have several breeders who were complaining of the lack of babies this summer. Throughout a series of environmental light manipulations, we were able to induce these reluctant pairs into production. So successfully, in fact, that one breeder came in complaining last week of having too many babies to feed. We must be careful what we pray for, because we just might get it!
Here are further details of environmental light manipulation:
1) Increasing day length stimulates gonadogenesis (the growth and activity of the gonad [ovary or testicle], which results in the organ's productive activity.)
2) Decreasing day length stimulates gonadogenesis.
3) Constancy of day length tends to favor gonadal regression.
During the productive cycle of the breeding season, most of my bird breeders work their lights up to a day length of 16 to 18 hours maximum. During normal weather cycles, and if all of the other idiosyncrasies are in order, we expect egg laying within one week of reaching the maximum day length. This summer one particular aviary had only two eggs at this time. Their maximum day length was 16 hours; we extended this with no improvement in production. Therefore, we took advantage of the paradoxical fact that decreasing day length will also stimulate gonadogenesis. We abruptly dropped the artificial lighting to six (6) hours per day and left it there for four weeks. At the end of four weeks, we started increasing the day length two hours a day until we were back to 16 hours. This bird breeder is now the one complaining that we have too many babies to feed. It is nice to be able to provide bird breeders with results just by environmental manipulation and not having to resort to drugs or hormones, which might harm a bird's reproductive capabilities.
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Sam Vaughn, DVM, Dip., ABVP-Avian Practice is an avian specialist based in Louisville, Kentucky. Certified in Avian Practice by the American Board of Veterinary Practitioners, Dr. Vaughn owns Avian Medical Services Inc. (an avicultural service and consultation practice) and is a partner in Veterinary Associates Stonefield, a full-service avian/exotic and small animal practice. Dr. Vaughn holds degrees in biology, chemistry and a Doctorate of Veterinary Medicine from Auburn University. Feel free to visit his web site at http://www.vetcity.com. Telephone consultations by appointment are available by calling (502) 245-7863.