WhenToBird

Hydroprogne caspia · Laridae

When Do Caspian Terns Arrive in California?

Adult Caspian Tern
Photo: Daughter Dad, CC BY 4.0 via iNaturalist

Caspian Terns reach California in early March, are common by early April, peak in the second week of August (12% of checklists), and most are gone by mid September.

When to look

First arrivalsMar 1-7early March
Common byApr 1-7early April
PeakAug 8-14the second week of August
Most gone bySep 15-21mid September

Best: the second week of August. First arrivals early March; most are gone by mid September. Peak: on about 12% of California checklists.

  1. Janrare
  2. Febrare
  3. Maruncommon
  4. Aprcommon
  5. Maycommon
  6. Juncommon
  7. Julpeak season
  8. Augpeak season
  9. Sepcommon
  10. Octrare
  11. Novrare
  12. Decrare

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

0%5%10%15%Jan 1-7: 1.0% of 112336 checklistsJan 8-14: 1.2% of 85518 checklistsJan 15-21: 1.2% of 86488 checklistsJan 22-31: 0.9% of 116174 checklistsFeb 1-7: 0.8% of 75171 checklistsFeb 8-14: 0.8% of 84467 checklistsFeb 15-21: 0.7% of 105683 checklistsFeb 22-28: 0.9% of 83396 checklistsMar 1-7: 0.9% of 77470 checklistsMar 8-14: 1.2% of 75180 checklistsMar 15-21: 1.8% of 80770 checklistsMar 22-31: 2.9% of 114116 checklistsApr 1-7: 4.4% of 84057 checklistsApr 8-14: 5.4% of 83692 checklistsApr 15-21: 6.3% of 89242 checklistsApr 22-30: 6.6% of 114289 checklistsMay 1-7: 6.6% of 85728 checklistsMay 8-14: 6.2% of 91984 checklistsMay 15-21: 6.1% of 75478 checklistsMay 22-31: 5.9% of 106250 checklistsJun 1-7: 6.4% of 70051 checklistsJun 8-14: 6.8% of 67485 checklistsJun 15-21: 7.0% of 66269 checklistsJun 22-30: 7.5% of 79172 checklistsJul 1-7: 8.7% of 62877 checklistsJul 8-14: 10% of 60328 checklistsJul 15-21: 11% of 59705 checklistsJul 22-31: 12% of 83796 checklistsAug 1-7: 13% of 60215 checklistsAug 8-14: 13% of 60172 checklistsAug 15-21: 12% of 59877 checklistsAug 22-31: 10% of 89107 checklistsSep 1-7: 8.2% of 72000 checklistsSep 8-14: 5.6% of 71228 checklistsSep 15-21: 3.6% of 76808 checklistsSep 22-30: 2.3% of 100204 checklistsOct 1-7: 1.6% of 76571 checklistsOct 8-14: 1.4% of 80874 checklistsOct 15-21: 1.2% of 74581 checklistsOct 22-31: 1.1% of 97498 checklistsNov 1-7: 1.3% of 70851 checklistsNov 8-14: 1.2% of 72431 checklistsNov 15-21: 1.1% of 66767 checklistsNov 22-30: 1.1% of 94737 checklistsDec 1-7: 1.1% of 65393 checklistsDec 8-14: 1.1% of 67449 checklistsDec 15-21: 0.9% of 83421 checklistsDec 22-31: 1.1% 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.

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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 all32%
  2. Kings CountyBest early September · 76 checklists that week, 3,688 in all29%
  3. Orange CountyBest early August · 3735 checklists that week, 244,559 in all28%
  4. San Francisco CountyBest the second week of July · 2074 checklists that week, 130,018 in all27%
  5. Marin CountyBest early August · 1988 checklists that week, 135,728 in all25%
  6. Solano CountyBest early August · 357 checklists that week, 25,325 in all23%

Best spots

Share of checklists at the peak
  1. Middle Harbor Shoreline ParkAlameda County, best mid May · 23 checklists that week, 2,089 in all99%
  2. Talbert MarshOrange County, best early August · 22 checklists that week, 476 in all96%
  3. Don Edwards San Francisco Bay National Wildlife Refuge (Ravenswood)San Mateo County, best early June · 32 checklists that week, 686 in all95%
  4. Sunset State Beach (Watsonville Slough)Santa Cruz County, best mid July · 25 checklists that week, 809 in all95%
  5. Elk RiverHumboldt County, best early August · 22 checklists that week, 655 in all94%

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

Best time of day

In California, the Caspian Tern is most often listed on checklists started between 6 and 8 am (5.3% of those checklists).

0%2%4%6%8%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: 6.3% of 186053 checklists7 am: 4.8% of 444086 checklists8 am: 4.4% of 535846 checklists9 am: 4.1% of 486061 checklists10 am: 3.9% of 411130 checklists11 am: 3.8% of 325798 checklists12 pm: 3.4% of 269132 checklists1 pm: 3.5% of 244762 checklists2 pm: 3.5% of 235420 checklists3 pm: 3.4% of 232365 checklists4 pm: 3.6% of 208688 checklists5 pm: 4.6% of 146104 checklists6 pm: 5.4% 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
January1.0%1.2%1.2%0.9%
February0.8%0.8%0.7%0.9%
March0.9%1.2%1.8%2.9%
April4.4%5.4%6.3%6.6%
May6.6%6.2%6.1%5.9%
June6.4%6.8%7.0%7.5%
July8.7%10%11%12%
August13%13%12%10%
September8.2%5.6%3.6%2.3%
October1.6%1.4%1.2%1.1%
November1.3%1.2%1.1%1.1%
December1.1%1.1%0.9%1.1%

Neighboring states

  • Nevada: arrives the second week of April, 5 weeks later than California
  • Utah: arrives early April, 4 weeks later than California
  • Oregon: arrives the second week of April, 5 weeks later than California
  • Idaho: arrives mid April, 6 weeks later than California

Common questions

When do Caspian Terns arrive in California?
Caspian Terns reach California in early March, are common by early April, peak in the second week of August (12% of checklists), and most are gone by mid September.
When do Caspian Terns leave California?
Most Caspian Terns have left California by mid September, when reports fall below half their usual rate. Stragglers are still reported until mid January.
When is the best time to see a Caspian Tern in California?
The Caspian Tern is reported most often in the second week of August, on about 12% of California checklists.
Where in California are Caspian Terns seen most often?
By county, Imperial County, Kings County, and Orange County have the highest peak reporting rates for the Caspian Tern (counties with at least 200 checklists).