Bluebird and Small Cavity Nester Conservation
Sialis - Bluebirds and other small cavity nesters
 
bluebirds

eggs

When will the first egg be laid?

first egg.  Zimmerman photo.

Most of us get ants in our pants waiting for that first bluebird egg of the season. Sometimes it seems like it is a long time coming. Sometimes we worry that the birds are laying too soon because the weather is still cold. Early clutches may succumb to hypothermia. But usually the birds know best, and wait until temperatures and food supplies are right.

If you want to see when the first egg in your area is typically laid, see my summary chart, or follow instructions below from Tina Mitchell of Coaldale, CO to generate your own report. You can get the information with just a few clicks of your mouse.

Jump to: Table | Factors influencing dates | Run your own report | Disclaimers | Errors | NestWatch | About the Table | Footnotes

Factors influencing when the first egg is laid:

  • Temperatures, food supply, availability of nesting sites, and competition among species are big factors.
  • One study found that first eggs for Western Bluebirds were significantly earlier (by about 18 days) in nestboxes versus natural cavities (Purcell 1997.)
  • Note that some states are large, with varied topography and different microclimates, and first eggs in different locations can vary quite a bit within the state, and from year to year. For example, in Montana, first eggs for MOBL's were listed as 3/3 in 2004 and 5/1/ in 2009.
  • Even in the same area there can be considerable variation. Some areas have very little data - for example, only one MOBL nesting was reported for British Columbia (BC) from 1997-2009.
  • Resident or more experienced bluebirds may lay eggs earlier than migrants or first year birds. Before laying, the female has to find a mate. If singles are scarce, that could slow them down.

About the Table: The table below shows the earliest reported date from 1997 (when data started being collected) through part of 2009. If a state had two earliest dates in different years, I used the earliest year listed.ND means no data reported for any bluebird species (Eastern/Mountain/Western.) There is a wealth of other data in the system that needs to be mined, and more is added each year. See footnotes.

First reported egg in NestWatch 1997-2009
United States
Canada
AL
3/1-EABL
2006
MA
3/24-EABL
2009
RI
5/1-EABL
2001
AB
4/15-EABL
4/21-MOBL
2008
2008
AK
ND
MD
3/7-EABL
2006
SC
3/13-EABL 2007
BC
5/5-MOBL
3/1-WEBL
1997
1997
AZ
5/1-EABL
4/11-WEBL
2005
2005
ME
4/22-EABL
2006
SD
4/20-EABL
2003
MB
4/28-MOBL
2009
AR
3/12-EABL
2001
MI
3/17*-EABL
5/13-WEBL
2005
2007
TN
2/28-EABL
2007
NB
ND
CA
2/28-WEBL
6/1-MOBL
2003
1997
MN 3/31-EABL 2007
TX
1/24-EABL
5/2-WEBL
2008
1997
NL
ND
CO
4/14-EABL
3/18-MOBL
4/1-WEBL

2007
2006
2007

MO 3/10-EABL
4/4-MOBL?
4/16-WEBL
2005
2006
2003
UT
4/11-MOBL
5/1-WEBL
2002
2006
NT
ND
CT
4/1-EABL
2002
MS 3/16*-EABL 2009
VT
4/4-EABL
2007
NS
ND
DE
4/1-EABL
2006
MT 5/14-EABL
3/3-MOBL
5/7-WEBL
2008
2004
1997
VA
3/15-EABL
* - MOBL
2000
NU
ND
FL
1/21-EABL
2006
NC 3/12-EABL 2006
WA
4/20-MOBL
4/4-WEBL
2005
2008
ON
4/17-EABL
1997
GA
3/4*-EABL
2009
ND
4/22-EABL
4/17-MOBL
2001
1998
WV
3/15-EABL
* - MOBL
2006
PE
ND
HI
ND
NE
4/1-EABL 1997
WI
3/29-EABL
2000
QC
5/6-EABL
1997
IA 5/30-WEBL 2009
NH
4/9-EABL
2008
WY
4/19-MOBL
2004
SK
ND
ID
4/15-WEBL
3/30-MOBL
2004
2007
NJ
3/28-EABL
* - MOBL
2007
      YT ND  
IL
3/22-EABL
2000
NM
3/30-EABL
5/10-MOBL
4/4-WEBL
2006
2005
2002
           
IN
3/10-EABL
2009
NY
3/27-EABL
1997
           
IA
4/7-EABL
2007
OH
3/3-EABL
4/26-MOBL
6/11-WEBL
2000
2000
2003
           
KS
4/6-EABL
2003
OK
3/1-EABL
2002
           
KY
3/12-EABL*
2008
OR
4/11-MOBL
4/6-WEBL
2004
2005
           
LA
2/12-EABL
2009
PA
3/16-EABL
* - MOBL
2000
 
 

Run your own report from Nestwatch data

  1. Go to the NestWatch Website
  2. Click on "Explore Data"
  3. Click on "Project-wide Reports"
  4. Choose "Species Summaries"
  5. Then, from the drop-down menu, choose your species (e.g., Eastern Bluebird) during "all seasons" in {select your state}.
  6. Uncheck any default selections, and click on "Total # of eggs & average clutch size"
  7. Hit "Export" and then "Open" (or Save")
  8. NestWatch will then export your data to an Excel file (it will go into a temporary folder). Open the second tab to see your data.

You can get "earliest 1st egg date," average 1st egg date," and "latest 1st egg date" for each NestWatch trail or group of nests since 1997. You can chose other options and narrow the report in lots of different ways--e.g., only a few years, just one state, U.S. only, etc. You can also sort on the various columns in the Excel Spreadsheet to organize it by state or whatever. Unfortunately because the of the way the dates are set up (MM/DD/YY), they don't sort numerically.

Statistical disclaimers: Of course not everyone who monitors a nestbox enters data into NestWatch's database, so the sample is biased in unknown (and mostly unknowable) ways. Also, there is no verification.

Errors: If anybody wants to use or publish this information, definitely go back to the database to verify, as there could be typos or things I missed! Some entries appear to be errors - see *footnotes. For example, there was one report of a Mountain Bluebird nesting in NJ - I seriously doubted that one and left it out. Be careful when drawing conclusions about which species nests earlier in a specific location, as first egg dates could be in wildly different parts of the state and during different years.

Try NestWatch: If you haven't entered your data into NestWatch in the past, give it a try! It's free, it's interesting, and most importantly, the data can help citizen and professional scientists figure out important stuff like the impact of climate change or land-use changes on wild birds. The project is managed by the Cornell Laboratory of Ornithology. The North American Bluebird Society used to have a Transcontinental Bluebird Trail monitoring database, but it is no longer in use, and they hope people will use NestWatch instead now.

* ? FOOTNOTES to Table

  • DATE ACCURACY?
    • One data point for GA indicated the first egg was laid 1/12/2006, but this appears to be an data entry error since all other dates are in March. Not included on table.
    • Same for MI - 01/20/2009, not included on table.
    • For MS, one entry said 2/2/2008, not included on table.
  • SPECIES ACCURACY?
    • One report for a Mountain Bluebird nesting in NJ with a first egg on 7/9/2000 - I'm guessing the data entry person picked the wrong species (should have been Eastern) so I left that out.
    • Four reports of MOBL nestings in PA not included (earliest egg was 4/27/2000)
    • One report of a MOBL nesting in VA on 4/12/2005 not included
    • One report of MOBL in WV on 5/9/2000 not included.
    • One report of WEBL in NY 5/22/2007 not included
    • Report of MOBL nesting in KY on 4/28/2007 not included
  • MORE THAN ONE SPECIES REPORTED BREEDING (obvious errors removed)
    UNITED STATES:
    AZ: Eastern Bluebird (EABL), Western (WEBL)
    CA: WEBL, (Mountain) MOBL
    CO: EABL, MOBL, WEBL
    ID: WEBL, MOBL
    MI:  EABL, WEBL (no MOBLs?)
    MO: EABL, MOBL?, WEBL
    MT: EABL, MOBL, WEBL
    ND:  EABL, MOBL
    NM: EABL, MOBL, WEBL
    OR: MOBL, WEBL
    TX: EABL, WEBL
    UT: MOBL, WEBL
    WA: MOBL, WEBL
    CANADA:
    AB: EABL, MOBL
    BC: MOBL, WEBL
  • NO DATA returned on query
    • United States: AK
    • Canada:  NB, NL, NT, SN, NU, PE, SK, YT

Related Links and More Information:


Every nest that is built and has eggs laid in it is a gift. Sometimes nature is cruel, but this has to be accepted.
- 10 year monitoring veteran responding to a Bluebird Nut Survey, 2005


HOME | Basics | Resources | House Sparrows | House Wrens | Nest/Egg ID | Site Map and Search | Suet Recipes | Tree Swallows | Contact me Bluebird Conservation

May all your blues be birds!

If you experience problems with the website/find broken links/have suggestions/corrections, please contact me!
The purpose of this site is to share information with anyone interested in bluebird conservation.
Feel free to link to it (preferred as I update content regularly), or use text from it for personal or educational purposes, with a link back to http://www.sialis.org or a citation for the author.
No permission is granted for commercial use.
Appearance of automatically generated Google or other ads on this site does not constitute endorsement of any of those services or products!

Photo in header by Wendell Long.
© Original photographs are copyrighted, and may not be used without the express permission of the photographer. Please honor their copyright protection.
See disclaimer, necessitated by today's sadly litigious world.
Last updated March 24, 2016. Design by Chimalis.

Chimalis