EGG-LAYING TIMINGS

The Bald Eagle nest cams from 2007-2016 are giving us priceless new information about breeding in the wild (as opposed to captivity). We now have some real numbers to crunch. Data about egg-laying collected from JudyB’s charts, the Hancock Wildlife Forum, the Channel Islands EagleCAM Forum, nest cam websites, and my own observations give reliable dates and times for 61 breeding seasons at 29 nests with 2-egg clutches, 38 seasons at 21 nests with 3-egg clutches, and 1 nest with a 4-egg clutch. Only nests with precise timings are included in this report.

Three charts below show the information collected. You can sort on a column by clicking its heading. Nest codes used here are listed in this chart. All times are local nest time and are given in 24-hour format without a colon (0000=midnight, 1200=noon).

Abbreviations:
h = hour
m = minute
d = day
< = before or by (not included in calculations)
~ = approximately (not included in calculations)

These data yield some general findings:

  • Most first eggs of a clutch are laid between about noon and midnight.
  • The eggs come at roughly 3-day or 4-day intervals. This is consistent with afternoon-evening layings: if another egg is not laid by the end of the third day, it is likely to come about a day later.
  • The shortest interval between one egg and the next was 68h40m or just under 3d (BC dl2 in 2016). The longest interval was 116h37m or nearly 5d (IA dec in 2010).
  • The interval from one egg to the next almost always increases with subsequent layings.
  • A particular female generally has a consistent pattern of timings. Some tend to lay eggs at 3-day intervals, others at 4-day intervals. A particular female also tends to lay at roughly the same time of day from year to year, although there are exceptions. If you sort on the Nest column in each chart you can observe the patterns and inconsistencies. See comments below the charts for further details.

2-egg clutches

  • About 82% (50 of 61 breedings) had a 3-day interval from the first to the second egg, with a mean average time of 73h21m.
  • About 18% (11 of 61 breedings) had a 4-day interval from the first egg to the second, with a mean average time of 94h34m.
  • Most females are consistent 3-day or 4-day layers from year to year (sort on the Nest column).
NESTEGG 1Time E1-E2EGG 2
BC dl23/10/16 155568h40m3/13/16 1335
CA cTH2/27/15 205769h12m3/2/15 1809
CA zPH2/25/10 173669h16m2/28/10 1452
PA han2/14/15 175470h51m2/17/15 1645
CA cTH2/15/13 2257
broke		71h3m2/18/13 2200
CA zSC2/24/13 2030
ravens pred		71h27m2/27/13 1957
ravens pred
BC dl23/28/14 160871h49m3/31/14 1557
VA riv2/12/15 1724
hatch fail		71h54m2/15/15 1718
CA trt2/12/11 164971h56m2/15/11 1645
CA zPH
new nest		3/6/12 1358
broke		72h3m3/9/12 1401
BC dl33/1/15 142372h4m3/4/15 1427
no hatch
WV shp2/6/13 180972h6m2/9/13 1815
FL nef11/14/13 134272h6m11/17/13 1348
TN har2/4/14 183572h21m2/7/14 1856
CA cWE2/28/09 173372h25m3/3/09 1758
WI e4k3/10/16 1557
juv BAEA pred		72h27m3/13/16 1724
juv BAEA pred
VA ccb2/8/12 174472h33m2/11/12 1817
FL nef11/16/14 125272h34m11/19/14 1326
BC dl23/10/15 1543
incub fail		72h38m3/13/15 1621
incub fail
MN bnd3/1/16 174072h46m3/4/16 1826
TN pgf
F & I		3/23/13 195572h51m3/26/13 2046
PA han2/18/16 151373h2m2/21/16 1615
no hatch
TN har1/27/16 175273h3m1/30/16 1855
TN har2/10/13 174573h11m2/13/13 1856
FL swf
new M		12/19/15 162573h15m12/22/15 1740
NJ duk2/18/16 161573h20m2/21/16 1735
BC sid3/4/10 183573h21m3/7/10 1956
raven pred
OR des3/24/10 2010
weather		73h21m3/27/10 2131
weather
TN har2/18/15 170473h22m2/21/15 1826
MD blk1/11/12 144473h25m1/14/12 1609
FL swf11/17/13 163773h41m11/20/13 1818
MN bnd2/28/15 155873h50m3/3/15 1748
GA ber1/7/16 172873h50m1/10/16 1918
CA cTH2/19/12 183173h56m2/22/12 2027
GA ber1/6/15 170074h6m1/9/15 1906
FL swf11/19/14 140774h9m11/22/14 1616
WI e4k3/2/12 163074h24m3/5/12 1854
MN bnd3/9/13 155274h30m3/12/13 1922
FL nef11/16/15 134974h53m11/19/15 1642
CA cWE
new F		2/23/15 1633
broke		75h2/26/15 1933
CA zPH2/25/09 142375h8m2/28/09 1731
ME br13/16/14 135575h10m3/19/14 1705
BC wht3/13/15 165775h22m3/16/15 2019
CA zPH2/24/08 132975h31m2/27/08 1700
IA dav2/7/13 143075h38m2/10/13 1808
GA ber1/14/14 1512
no hatch		75h49m1/17/14 1901
BC wht3/13/11 163175h56m3/16/11 2027
FL swf11/26/12 134476h54m11/29/12 1838
WV shp2/5/12 173477h37m2/8/12 2311
CA zSC3/2/12 184177h45m3/6/12 0026
BC hrn3/22/11 194491h39m3/26/11 1523
CA cWE2/11/16 224292h2/15/16 1842
BC har4/3/16 202192h46m4/7/16 1707
BC har3/24/15 204893h21m3/28/15 1809
MT lib3/16/09 182594h25m3/20/09 1650
CA cTH2/25/16 2206
no hatch		94h52m2/29/16 2058
no hatch
BC hrn3/30/14 2019
no hatch		94h53m4/3/14 1912
BC har4/4/13 201095h34m4/8/13 1944
NC jor2/28/14 185895h43m3/4/14 1841
CA cTH2/17/10 184696h14m2/21/10 1900
CA cTH2/17/11 203198h52m2/21/11 2323
broke
© elfruler 2017

3-egg clutches

  • About 92% (35 of 38 breedings) had a 3-day interval from the first to the second egg, with a mean average time of 72h16m.
  • About 8% (3 of 37 breedings) had a 4-day interval from the first egg to the second, with a mean average time of 93h57m. (Note the contrast with 2-egg clutches, where a larger percentage (18%) had a 4-day interval.)
  • The proportion between 3-day intervals and 4-day intervals from the second to the third egg is more balanced than with 2-egg clutches:
    • About 55% (16 of 29 nests with precise timings) had a 3-day interval, with a mean average time of 74h12m.
    • About 45% (13 of 29 nests) had a 4-day interval, with a mean average time of 96h46m.
  • As with 2-egg clutches, eagles at particular nests usually had a consistent pattern of laying from year to year (sort on the Nest column), either 3 days both between first and second eggs and between second and third eggs, or 3 days between first and second egg and 4 days between second and third eggs. Where the pattern is not consistent, possible reasons may be a change of mate (as at CA trt in 2014), inclement weather, intruders, etc.
  • The 2010 season at IA dec was unusual in that the interval between the second and third eggs, 116h37m, was  more than 20 hours longer than the next longest interval, at CA trt in 2013 (97h58m).  If the third egg-laying at IA dec in 2010 is excluded from the calculations, about 57% (16 of 28 breedings) had a 3-day interval, with a mean average time of 74h12m, and 43% (12 of 28 breedings) had a 4-day interval, with a mean average time of 94h55m.
NESTEGG 1Time E1-E2EGG 2Time E2-E3EGG 3
VA nbg1/31/10 141469h36m2/3/10 115072h39m2/6/10 1229
CA trt
new M		2/6/13 1714
disappeared		70h20m2/9/13 153497h58m2/13/13 1732
MN dnr1/25/16 151870h27m1/28/16 134574h47m1/31/16 1632
IA dav2/11/12 145370h40m2/14/12 133375h2m2/17/12 1635
IA dnn3/11/16 142970h59m3/14/16 142890h13m3/18/16 0841
CA trt2/6/09 180071h17m2/9/09 17172/13/09 pm
or 2/14/09 am
IA dec2/18/16 202871h18m2/21/16 194695h13m2/25/16 1859
infertile
BC laf3/15/14 163971h21m3/18/14 1600
hatch fail		~75h3/21/14~1900
PA pit2/19/14 164571h33m2/22/14 161874h21m2/25/14 1839
CO fsv2/17/13 180971h45m2/20/13 175472h52m2/23/13 1846
IL umr
1F & 2M		2/1/16 155771h48m2/4/16 154575h4m2/7/16 1849
VA riv2/16/16 152971h56m2/19/16 15252/23/16<2330
no hatch
CO fsv2/14/15 181772h2/17/15 181773h41m2/20/15 1958
MD blk1/13/14 1623
no hatch		72h5m1/16/14 1628<1/20/14 0847
TN pgf
I & J		2/18/16 0823
no hatch		72h7m2/21/16 0830
no hatch		96h50m2/25/16 0920
no hatch
CA trt2/6/15 153672h8m2/9/15 154473h12m2/12/15 1656
TN pgf
F & I		3/21/16 1911
no hatch		72h14m3/24/16 1925
no hatch		< 3/29/16 0730
no hatch
BC laf3/13/13 161072h15m3/16/13 162572h1m3/19/13 1626
CA trt2/15/10 161572h17m2/18/10 163274h13m2/21/10 1845
OK snr2/6/09 1547
no hatch		72h23m2/9/09 1610
no hatch		2/13/09 pm
WV shp2/17/14 175472h25m2/20/14 1819<2/24/14?0545
WV shp2/12/15 153972h27m2/15/15 160674h19m2/18/15 1825
IA dec2/23/14 165572h38m2/26/14 173397h10m3/2/14 1843
MN bnd3/7/14 164972h39m3/10/14 182875h32m3/13/14 2200
VA nbg2/10/09 162572h40m2/13/09 170591h3m2/17/09 1208
IA dec2/18/15 180772h54m2/21/15 190195h56m2/25/15 1857
CA cWE2/23/11 174172h59m2/26/11 184097h50m?3/2/11 2030?
BC sid3/7/11 154473h4m3/10/11 164896h16m3/14/11 1804
IA dec2/23/11 173373h9m2/26/11 184296h5m3/2/11 1847
NJ duk2/28/11 140073h9m3/3/11 15093/6/11 <1616
IA dec2/17/12 194773h19m2/20/12 210694h59m2/24/12 2005
VA nbg2/3/11 144973h36m2/6/11 162573h30m2/9/11 1755
BC wht3/16/14 163774h3m3/19/14 184073h23m3/22/14 2003
accid broke
CA cWE2/22/13 181074h47m2/25/13 205791h58m3/1/13 1655
IA dec2/25/10 192674h47m2/28/10 2213116h37m
4d20h37m		3/5/10 1850
TN pgf
F & I		3/27/15 2041
no hatch		93h47m3/31/15 1828
no hatch		71h7m4/3/15 1735
no hatch
OH avn2/26/16 204593h50m3/1/16 1835<3/5/16 am
CA cWE2/18/12 202494h13m2/22/12 183795h15m2/26/12 1752
WV shp<2/4/08 09172/6/08 200081h30m2/10/08 0530
© elfruler 2017

4-egg clutches

  • These are rare among Bald Eagles. From 2006-2016 only three nests with 4 eggs have been documented by direct observation (WV shp in 2010, MT cfr in 2011, and OK snr in 2013). Of those only WV shp has precise observed timings.
NESTEGG 1Time
E1-E2		EGG 2Time
E2-E3		EGG 3Time
E3-E4		EGG 4
WV shp2/2/10 2215
weather		87h57m2/6/10 1412
weather		75h34m2/9/10 1746
disappeared		92h56m2/13/10 1442
© elfruler 2017
  • The first three of the eggs were lost in snowstorms; the fourth ended in a successful fledge. Note that the timings between eggs alternate between 4-day and 3-day intervals.

© elfruler 2016, 2017. Revised 1/5/17

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