Friday, May 16, 2008

2008 Purple Martin Colony Update

On April 19th I lowered my gourd racks to find my first clutch of 5 eggs for the season, and then on May 1st I had 18 nests containing a total of 88 eggs. Also on this day I found an 8-egg clutch in one of my gourds which is very rare. Over the years I have had several 7-egg clutches, but the only other time I had 8 was in 1996 in a wooden house I built which turned out to be a renest attempt. Purple martins sometimes will attempt another clutch of eggs if the first fails to hatch or is lost due to predators.
Normally with clutches of 7 or 8 not all of them are destined to hatch. I had an exception back in 2002 when a clutch of 7 all hatched, but only 5 of those fledged. At my particular site in the beginning (1995-which consisted of houses only) the average clutch size ranged from 4-5 eggs with an occasional clutch of 6. Ever since I went to an all gourd colony in 2001 I’ve noted an increase in 6-egg clutches, which is one of the main reasons why I converted. Gourds, due to their roominess and other attributes, have shown to increase clutch size and produce greater reproductive success. Hopefully I will luck out this time and have all 8 hatch and fledge. I’ll keep everyone up to date on this particular clutch as the season progresses. As of May 13th I have 96 eggs and 12 nestlings, which tallies up to a total of 108 eggs laid thus far.
The nestlings in this photo are approximately 7 days old, determined by using a set of laminated life-size photos of a developing nestling that can be purchased from the PMCA. You take the nestling from the nest and lay it on top of the photo that most closely matches its size and voila you have its age. Note the large uneaten green darner dragonfly amongst the nestlings. Surprisingly it still has it head- usually the adults will remove it so the dragonfly doesn’t bite on the way down. Also this is a rather large dragonfly for these young nestlings. I found a dead one back in 2002 after it had choked on one this large.
In another nest I found what is known as a “capped” egg. If one or more eggshell hemispheres remain in the nest after a nestling hatches chances are a half could end up attached to the end of any remaining unhatched eggs as seen in the photo. If this happens the nestling inside the egg may have difficulty hatching. I gently picked up the egg, removed the cap and placed it back in the nest. Most times the adults will eat the remaining egg shell (for its calcium content) and other times fly away from the colony to drop them off just like they do with the nestling’s fecal sacs, because dropping either of these on the ground below the colony could possibly attract predators.
Just one more reason why it is so important for martin landlords to perform regular nest checks on their colony. Another update will appear at a later date.

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