When will the first egg be laid?

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.

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:

• How many eggs will a female lay?
• How many broods will a bluebird have?
• Why didn’t the egg(s) hatch?
• Hypothermia, preventing
• Nesting biology, by species
• Egg production
• Nest, egg and young ID guide
• Photo album showing nests, eggs, young and adults of various species side by side
• Should I remove unhatched eggs from the nest?
• Can I incubate an egg myself?
• Why we get goopy over bluebirds
• The downside of bluebirding
• Competition among species