The case of the missing eggs

[birdgardener]

On June 10 all eight gourds had eggs. One week later, June 17, one gourd had 0 eggs that had 4 eggs 1 week earlier. There was no nest disturbance and I looked for leaves covering them up to no avail. I have a predator guard, so I don't think any climbing animal could have gotten to them. On June 24 there were 4 eggs and on June 30 there were 5 eggs in this same gourd. They all ended up fledging except for one unhatched egg. I also had one gourd with 5 eggs, but only 1 hatched. In another gourd there were 5 eggs, but only 2 hatched. In another gourd 5 eggs were laid, but none hatched. In another gourd 6 eggs were laid, all hatched, and all fledged. Any thoughts on the discrepancies? In total 25 fledged. The last 4 fledged on August 7. This is my second year. They kept coming back for visits. Their last visit was on August 21. Looking forward to when the kids come back next year.

Dan in Buffalo, MN

[Eugene Feltmann]

We are in New Germany, Mn. Also second year landlords. We had some similar problems with missing eggs, not all eggs hatched, and also some nest where not all survived.
No insect, mite, or predator problems. I talked with a man from Waconia who has had purple martins for years and he stated that he has never seen a year like this. He had some of the same problems and thought it was just the weather. Martins still flew over this morning, August 26, so there are still some around. We learn something new every year.

[Eugene Feltmann]

Just an added note, we fledged 44 birds this year.

[randyM]

It is not uncommon for nests to have some, or all, eggs that don't hatch or go missing. Unhatched full (or partial) clutches of eggs can be due to infertility issues with either adult. Weather conditions during incubation also (too hot, too cold, too wet, too windy) can cause some eggs to not hatch. Ambient temps too hot or too cold may cause a large swing in temperature inside the developing eggs. Embryos, especially in the mid-later stages of development may be susceptible to death before hatching due to wide swings in temperature, especially when the female is away from the nest for an extended period of time while feeding or due to disturbance, etc. Wet nests can cause cooler egg temps due to evaporation, which can affect hatching rate. Windy conditions causing swinging gourds or swaying housing can allow eggs to bump together and cause hairline cracks that can allow bacteria to enter the egg and kill the embryo inside. Inexperianced SY females may not be as attentive to nests/eggs during incubation as ASY females, resulting in some embryos getting too cold and dying prior to hatching in some SY nests. House sparrows, starlings or sub adult male martins may remove some or all eggs from nests during incubation. A nesting adult may die or become ill, causing the nest to be abandoned, resulting in no eggs hatching. These are a few common reasons some eggs may not hatch in a given nest or collective colony during any given year. I've had a colony for about 10 years now and have had over 4300 eggs observed, with only 84% of those eggs documented as hatching. That boils down to roughly about 1 out of every 5 eggs laid not hatching. Each year may vary...I've had well over 90% of martin eggs hatch at my colony in a year and have had a hatch rate barely above 75% in another year. Hopefully, you have a higher hatching rate at your colony next year compared to 2025, but I would not expect much over 90% hatch rate in any given year.
Best of luck in 2026!

[Dave Reynolds]

.. randym ... Great advice... This was an odd year for us in the Southeastern Ohio. Most birds arrived earlier then before.. Then the Spring was extra wet and cool.. A lot of eggs did not hatch because of the weather. But all in all we had a good year.. Enjoy the ones you have..

Dave

[Bird Brain]

Randy said it perfectly. I would add that the female knows immediately if the egg is a dud and will never hatch. She will sometimes remove the dud egg herself to make room for the good eggs or to start a new nest attempt. Based on Randy's documented hatch rate, it also appears that Northern Martin nests have a lower hatch rate than Southern Martin nests. I'm in Texas and my hatch rate is way above 90%. Probably closer to 95%, even with crappy weather.

[birdgardener]

Thanks for all the feedback.

Dan