WhenToBird

Vireo cassinii · Vireonidae

When Do Cassin's Vireos Arrive in Arizona?

Adult Cassin's Vireo
Photo: David Anderson, CC BY 4.0 via iNaturalist

Cassin's Vireos arrive in Arizona in early March, peak in the second week of April (3.3% of checklists), and most are gone by mid May.

When to look

First arrivalsMar 1-7early March
Common byMar 1-7early March
PeakApr 8-14the second week of April
Most gone byMay 15-21mid May

Best: the second week of April. First arrivals early March; most are gone by mid May. Peak: on about 3.3% of Arizona checklists.

  1. Januncommon
  2. Febuncommon
  3. Marcommon
  4. Aprpeak season
  5. Maycommon
  6. Junrare
  7. Julnot usually seen
  8. Augcommon
  9. Sepcommon
  10. Octcommon
  11. Novcommon
  12. Decuncommon

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

0%1%2%3%4%Jan 1-7: 0.6% of 34758 checklistsJan 8-14: 0.7% of 29835 checklistsJan 15-21: 0.5% of 29279 checklistsJan 22-31: 0.6% of 39716 checklistsFeb 1-7: 0.5% of 27299 checklistsFeb 8-14: 0.5% of 28703 checklistsFeb 15-21: 0.6% of 35357 checklistsFeb 22-28: 0.6% of 29889 checklistsMar 1-7: 0.7% of 29932 checklistsMar 8-14: 0.9% of 32982 checklistsMar 15-21: 1.4% of 34731 checklistsMar 22-31: 2.4% of 50213 checklistsApr 1-7: 3.3% of 35788 checklistsApr 8-14: 3.2% of 38087 checklistsApr 15-21: 3.4% of 41520 checklistsApr 22-30: 3.1% of 55218 checklistsMay 1-7: 2.3% of 39688 checklistsMay 8-14: 1.8% of 39398 checklistsMay 15-21: 1.2% of 29562 checklistsMay 22-31: 0.5% of 36774 checklistsJun 1-7: 0.2% of 21313 checklistsJun 8-14: 0.1% of 19129 checklistsJun 15-21: 0% of 17922 checklistsJun 22-30: 0% of 21188 checklistsJul 1-7: 0% of 17325 checklistsJul 8-14: 0.1% of 16463 checklistsJul 15-21: 0.1% of 18642 checklistsJul 22-31: 0.1% of 31215 checklistsAug 1-7: 0.1% of 28163 checklistsAug 8-14: 0.3% of 31329 checklistsAug 15-21: 0.9% of 23878 checklistsAug 22-31: 1.2% of 28508 checklistsSep 1-7: 2.2% of 20878 checklistsSep 8-14: 2.4% of 19671 checklistsSep 15-21: 2.4% of 19859 checklistsSep 22-30: 2.1% of 25179 checklistsOct 1-7: 2.0% of 19420 checklistsOct 8-14: 1.9% of 21925 checklistsOct 15-21: 1.7% of 20995 checklistsOct 22-31: 1.7% of 29258 checklistsNov 1-7: 1.6% of 21269 checklistsNov 8-14: 1.4% of 22753 checklistsNov 15-21: 1.1% of 21982 checklistsNov 22-30: 1.1% of 29475 checklistsDec 1-7: 1.0% of 20810 checklistsDec 8-14: 1.1% of 22229 checklistsDec 15-21: 1.2% of 25148 checklistsDec 22-31: 0.7% of 39567 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 Arizona 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 Arizona

Best counties

Share of checklists at the peak
  1. Santa Cruz CountyBest early October · 1562 checklists that week, 162,726 in all6.6%
  2. Cochise CountyBest the second week of September · 2470 checklists that week, 190,093 in all4.6%
  3. Apache CountyBest the second week of September · 442 checklists that week, 12,931 in all4.4%
  4. Navajo CountyBest the second week of September · 473 checklists that week, 18,838 in all4.1%
  5. Coconino CountyBest the second week of September · 2051 checklists that week, 90,870 in all4.0%
  6. Yavapai CountyBest late April · 4118 checklists that week, 83,606 in all3.9%

Best spots

Share of checklists at the peak
  1. Leslie Canyon National Wildlife RefugeCochise County, best the second week of September · 20 checklists that week, 253 in all48%
  2. Desert Foothills Land TrustMaricopa County, best the second week of April · 21 checklists that week, 687 in all39%
  3. Posta Quemada CanyonPima County, best early April · 25 checklists that week, 764 in all33%
  4. Butterfly SpringYavapai County, best early September · 23 checklists that week, 550 in all33%
  5. Tanque Verde CreekPima County, best the second week of April · 67 checklists that week, 2,051 in all31%

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

Best time of day

In Arizona, the Cassin's Vireo is most often listed on checklists started between 6 and 8 am (2.1% of those checklists).

0%1%2%3%12 am: too few checklists (488) to judge1 am: too few checklists (503) to judge2 am: too few checklists (489) to judge3 am: too few checklists (735) to judge4 am: too few checklists (4115) to judge5 am: 1.0% of 38350 checklists6 am: 2.0% of 118786 checklists7 am: 2.2% of 183415 checklists8 am: 2.0% of 187346 checklists9 am: 1.6% of 151342 checklists10 am: 1.1% of 124522 checklists11 am: 1.0% of 97088 checklists12 pm: 1.0% of 78110 checklists1 pm: 0.9% of 73059 checklists2 pm: 0.7% of 68912 checklists3 pm: 0.6% of 68060 checklists4 pm: 0.4% of 69387 checklists5 pm: 0.3% of 52951 checklists6 pm: 0.1% of 31061 checklists7 pm: too few checklists (16076) to judge8 pm: too few checklists (5352) to judge9 pm: too few checklists (2369) to judge10 pm: too few checklists (1100) to judge11 pm: too few checklists (604) 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
January0.6%0.7%0.5%0.6%
February0.5%0.5%0.6%0.6%
March0.7%0.9%1.4%2.4%
April3.3%3.2%3.4%3.1%
May2.3%1.8%1.2%0.5%
June0.2%0.1%0%0%
July0%0.1%0.1%0.1%
August0.1%0.3%0.9%1.2%
September2.2%2.4%2.4%2.1%
October2.0%1.9%1.7%1.7%
November1.6%1.4%1.1%1.1%
December1.0%1.1%1.2%0.7%

Neighboring states

  • New Mexico: arrives mid August, 22 weeks later than Arizona
  • Nevada: arrives the second week of April, 5 weeks later than Arizona
  • Utah: arrives late August, 23 weeks later than Arizona
  • California: arrives the second week of April, 5 weeks later than Arizona

Common questions

When do Cassin's Vireos arrive in Arizona?
Cassin's Vireos arrive in Arizona in early March, peak in the second week of April (3.3% of checklists), and most are gone by mid May.
When do Cassin's Vireos leave Arizona?
Most Cassin's Vireos have left Arizona by mid May, when reports fall below half their usual rate.
When is the best time to see a Cassin's Vireo in Arizona?
The Cassin's Vireo is reported most often in the second week of April, on about 3.3% of Arizona checklists.
Where in Arizona are Cassin's Vireos seen most often?
By county, Santa Cruz County, Cochise County, and Apache County have the highest peak reporting rates for the Cassin's Vireo (counties with at least 200 checklists).