Your questions, answered: Will the third egg hatch? Why did the first two eaglets hatch so close together?

It’s April 7 and a lot of you are wondering about the third egg. Will it hatch? It could! It has been almost 34 days since Mom laid her third egg, which is 33 days and 20 hours old as I write this. But her third egg almost always hatches 36 to 37 days after it was laid. If she goes 36 days, which is fairly common, hatch should happen on April 9th. We could see pip later today or tomorrow.

April 7, 2020: D34 and D35

April 7, 2020: D34 and D35

What was up with that same day hatch?

We’ve seen eaglets hatch within around a day of one another, but we’ve never seen them hatch within nine hours of one another. Is there anything in Mom’s reproductive record that might point to an answer? Let’s take a look!

Year1st egg 2nd egg 3rd egg hatch Lay datesHatch dates
202039 days36 daysN/A 2/26 | 2/29 | 3/4 4/5 | 4/5 | N/A
2019N/A37 days37 days 2/22 | 2/26 | 3/2N/H | 4/4 | 4/7
201840 days38 days36 days 2/21 | 2/24 | 2/28 4/1 | 4/2 | 4/4
201740 days38 days37 days 2/20 | 2/23 | 2/27 3/31 | 4/1 | 4/4
2016N/A38 days36 days 2/18 | 2/21 | 2/25N/H | 3/29 | 3/31
201537 days36 days36 days 2/18 | 2/21 | 2/25 3/27 | 3/29 | 4/02
201438 days36 days36 days 2/23 | 2/26 | 3/24/2 | 4/3 | 4/7
201239 days37 days36 days 2/17 | 2/20 | 2/243/27 | 3/28 | 3/31
201137 days36 days35 days2/23 | 2/26 | 3/24/1 | 4/3 | 4/6
201037 days37 days35 days2/25 | 2/28 | 3/54/3 | 4/6 | 4/9

There isn’t really anything that sticks out. In 2020, Mom’s first egg took just a tiny bit longer to hatch (39 days versus an average of 38 days) while her second egg hatched a little more quickly than normal (36 days versus an average of 37 days).  But her record shows other years where eggs developed a little slower or a little faster without hatching especially close together. 

Could temperature have something to do with it? Perhaps Mom was off the eggs a bit more in nice weather, or maybe it was cold enough that she dropped her body temperature a little to help stay warm over the first few days? I looked at the average daytime temperature between the first and second egg for the past five years. 

  • 2020 (2/26 – 2/29): Average temperature: 20.8 F
  • 2018 (2/21 – 2/24): Average temperature: 24.6 F
  • 2017 (2/20 – 2/23): Average temperature: 47.0 F
  • 2016 (2/18 – 2/21): Average temperature: 36.2 F
  • 2015 (2/18 – 2/21: Average temperature: 7.6 F

I didn’t bother to go any further – this year was just a tiny bit colder and drier than average over those three days, but we had colder/drier and warmer/wetter periods that didn’t produce unusual results. It doesn’t appear to be related to temperature or weather. 

So what happened? We often look at factors like daylight length, weather, and temperature to explain nest events. But this appears to be more about math and statistics. As the chart shows, neither egg is an outlier in and of itself, but each egg’s slight deviation – one a little faster than normal and one a little slower than normal – aligned to produce an unusual event: two hatches just nine hours apart! We’ll see how long the third egg takes and whether or not that turns into anything unusual. Tick tock hatch clock!