WhenToBird

Sterna forsteri · Laridae

When Do Forster's Terns Arrive in California?

Adult Forster's Tern
Photo: Aitor, CC BY 4.0 via iNaturalist

Forster's Terns reach California in mid March, are common by late March, peak in late July (5.5% of checklists), and most are gone by early December.

When to look

First arrivalsMar 15-21mid March
Common byMar 22-31late March
PeakJul 22-31late July
Most gone byDec 1-7early December

Best: late July. First arrivals mid March; most are gone by early December. Peak: on about 5.5% of California checklists.

  1. Jancommon
  2. Febuncommon
  3. Marcommon
  4. Aprpeak season
  5. Maypeak season
  6. Junpeak season
  7. Julpeak season
  8. Augpeak season
  9. Sepcommon
  10. Octcommon
  11. Novcommon
  12. Deccommon

Darker months: more checklists report it. Outlined: peak month.

0%2%4%6%Jan 1-7: 2.3% of 112336 checklistsJan 8-14: 2.2% of 85518 checklistsJan 15-21: 2.2% of 86488 checklistsJan 22-31: 1.9% of 116174 checklistsFeb 1-7: 1.7% of 75171 checklistsFeb 8-14: 1.6% of 84467 checklistsFeb 15-21: 1.5% of 105683 checklistsFeb 22-28: 1.7% of 83396 checklistsMar 1-7: 1.7% of 77470 checklistsMar 8-14: 1.6% of 75180 checklistsMar 15-21: 1.8% of 80770 checklistsMar 22-31: 2.2% of 114116 checklistsApr 1-7: 3.3% of 84057 checklistsApr 8-14: 4.0% of 83692 checklistsApr 15-21: 4.6% of 89242 checklistsApr 22-30: 5.2% of 114289 checklistsMay 1-7: 5.2% of 85728 checklistsMay 8-14: 4.5% of 91984 checklistsMay 15-21: 4.3% of 75478 checklistsMay 22-31: 4.2% of 106250 checklistsJun 1-7: 4.2% of 70051 checklistsJun 8-14: 4.1% of 67485 checklistsJun 15-21: 4.2% of 66269 checklistsJun 22-30: 4.7% of 79172 checklistsJul 1-7: 5.2% of 62877 checklistsJul 8-14: 5.3% of 60328 checklistsJul 15-21: 5.5% of 59705 checklistsJul 22-31: 5.4% of 83796 checklistsAug 1-7: 5.6% of 60215 checklistsAug 8-14: 5.2% of 60172 checklistsAug 15-21: 4.6% of 59877 checklistsAug 22-31: 4.3% of 89107 checklistsSep 1-7: 4.2% of 72000 checklistsSep 8-14: 3.7% of 71228 checklistsSep 15-21: 3.1% of 76808 checklistsSep 22-30: 2.8% of 100204 checklistsOct 1-7: 2.6% of 76571 checklistsOct 8-14: 2.7% of 80874 checklistsOct 15-21: 2.5% of 74581 checklistsOct 22-31: 3.0% of 97498 checklistsNov 1-7: 3.1% of 70851 checklistsNov 8-14: 2.8% of 72431 checklistsNov 15-21: 2.8% of 66767 checklistsNov 22-30: 2.5% of 94737 checklistsDec 1-7: 2.2% of 65393 checklistsDec 8-14: 2.4% of 67449 checklistsDec 15-21: 1.9% of 83421 checklistsDec 22-31: 2.1% of 124993 checklistsJanFebMarAprMayJunJulAugSepOctNovDec
Share of complete checklists reporting it, by week (4 per month). Grey bars: fewer than 10 checklists, not counted.

Frequency is the share of complete checklists in California that listed the bird, 2016–2025. It is not a head count, and it follows where and when people go birding. How to read it.

JanFebMarAprMayJunJulAugSepOctNovDec
today
Second week of November

Each county is shaded by the share of complete checklists there that listed the bird, blended with the weeks either side. Darker is more often. It follows where people watch birds, not how many birds there are. How to read it.

Embed this map on your site

Where in California

Best counties

Share of checklists at the peak
  1. Imperial CountyBest the second week of August · 229 checklists that week, 24,551 in all30%
  2. Orange CountyBest late June · 4557 checklists that week, 244,559 in all22%
  3. Santa Clara CountyBest mid July · 3099 checklists that week, 201,483 in all20%
  4. Solano CountyBest mid July · 394 checklists that week, 25,325 in all19%
  5. Alameda CountyBest mid July · 2490 checklists that week, 161,052 in all19%
  6. Kings CountyBest late May · 99 checklists that week, 3,688 in all16%

Best spots

Share of checklists at the peak
  1. Mountain View Tidal MarshSanta Clara County, best late July · 20 checklists that week, 771 in all98%
  2. Shoreline at Mountain View Park (Shoreline Lake)Santa Clara County, best early August · 68 checklists that week, 4,342 in all97%
  3. Hayward Regional Shoreline (south)Alameda County, best late May · 20 checklists that week, 327 in all96%
  4. Santa Ana River TrailOrange County, best late June · 23 checklists that week, 1,289 in all96%
  5. Napa-Sonoma Marshes Wildlife AreaSolano County, best late August · 33 checklists that week, 671 in all96%
  6. Crittenden Marsh (Jogel Slough)Santa Clara County, best the second week of August · 20 checklists that week, 158 in all95%

Busy spots report more of everything; compare the checklist counts before you drive anywhere.

Best time of day

In California, the Forster's Tern is most often listed on checklists started between 8 and 10 am (3.4% of those checklists).

0%1%2%3%4%12 am: too few checklists (1688) to judge1 am: too few checklists (1451) to judge2 am: too few checklists (1402) to judge3 am: too few checklists (1743) to judge4 am: too few checklists (4647) to judge5 am: too few checklists (32158) to judge6 am: 3.4% of 186053 checklists7 am: 3.3% of 444086 checklists8 am: 3.5% of 535846 checklists9 am: 3.3% of 486061 checklists10 am: 3.3% of 411130 checklists11 am: 3.2% of 325798 checklists12 pm: 3.2% of 269132 checklists1 pm: 3.6% of 244762 checklists2 pm: 3.2% of 235420 checklists3 pm: 3.0% of 232365 checklists4 pm: 2.9% of 208688 checklists5 pm: 3.3% of 146104 checklists6 pm: 3.2% of 96867 checklists7 pm: too few checklists (50942) to judge8 pm: too few checklists (14803) to judge9 pm: too few checklists (5561) to judge10 pm: too few checklists (3546) to judge11 pm: too few checklists (2092) to judge12a3a6a9a12p3p6p9p
Share of checklists started in each local hour that reported it. It reflects when people go birding as well as when birds are active. Grey hours have too few checklists (under 2% of the state’s, or under 200) to judge.
Week-by-week table
MonthDays 1-78-1415-2122-end
January2.3%2.2%2.2%1.9%
February1.7%1.6%1.5%1.7%
March1.7%1.6%1.8%2.2%
April3.3%4.0%4.6%5.2%
May5.2%4.5%4.3%4.2%
June4.2%4.1%4.2%4.7%
July5.2%5.3%5.5%5.4%
August5.6%5.2%4.6%4.3%
September4.2%3.7%3.1%2.8%
October2.6%2.7%2.5%3.0%
November3.1%2.8%2.8%2.5%
December2.2%2.4%1.9%2.1%

Neighboring states

  • Nevada: arrives mid April, 4 weeks later than California
  • Utah: arrives mid April, 4 weeks later than California
  • Oregon: arrives late April, 5 weeks later than California
  • Idaho: arrives late April, 5 weeks later than California

Common questions

When do Forster's Terns arrive in California?
Forster's Terns reach California in mid March, are common by late March, peak in late July (5.5% of checklists), and most are gone by early December.
When do Forster's Terns leave California?
Most Forster's Terns have left California by early December, when reports fall below half their usual rate. Stragglers are still reported until early February.
When is the best time to see a Forster's Tern in California?
The Forster's Tern is reported most often in late July, on about 5.5% of California checklists.
Where in California are Forster's Terns seen most often?
By county, Imperial County, Orange County, and Santa Clara County have the highest peak reporting rates for the Forster's Tern (counties with at least 200 checklists).