WhenToBird

Molothrus aeneus · Icteridae

When Do Bronzed Cowbirds Arrive in Arizona?

Adult Bronzed Cowbird
Photo: Jo Roberts, CC BY 4.0 via iNaturalist

Bronzed Cowbirds reach Arizona in mid April, are common by early May, peak in late June (6.4% of checklists), and most are gone by late July.

When to look

First arrivalsApr 15-21mid April
Common byMay 1-7early May
PeakJun 22-30late June
Most gone byJul 22-31late July

Best: late June. First arrivals mid April; most are gone by late July. Peak: on about 6.4% of Arizona checklists.

  1. Janrare
  2. Febrare
  3. Marrare
  4. Apruncommon
  5. Maypeak season
  6. Junpeak season
  7. Julpeak season
  8. Auguncommon
  9. Seprare
  10. Octrare
  11. Novrare
  12. Decrare

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

0%2%4%6%8%Jan 1-7: 0.3% of 34758 checklistsJan 8-14: 0.4% of 29835 checklistsJan 15-21: 0.4% of 29279 checklistsJan 22-31: 0.3% of 39716 checklistsFeb 1-7: 0.3% of 27299 checklistsFeb 8-14: 0.2% of 28703 checklistsFeb 15-21: 0.3% of 35357 checklistsFeb 22-28: 0.3% of 29889 checklistsMar 1-7: 0.3% of 29932 checklistsMar 8-14: 0.3% of 32982 checklistsMar 15-21: 0.3% of 34731 checklistsMar 22-31: 0.4% of 50213 checklistsApr 1-7: 0.6% of 35788 checklistsApr 8-14: 1.0% of 38087 checklistsApr 15-21: 1.1% of 41520 checklistsApr 22-30: 1.8% of 55218 checklistsMay 1-7: 3.4% of 39688 checklistsMay 8-14: 4.8% of 39398 checklistsMay 15-21: 6.0% of 29562 checklistsMay 22-31: 6.6% of 36774 checklistsJun 1-7: 6.0% of 21313 checklistsJun 8-14: 6.0% of 19129 checklistsJun 15-21: 6.5% of 17922 checklistsJun 22-30: 6.4% of 21188 checklistsJul 1-7: 6.2% of 17325 checklistsJul 8-14: 5.8% of 16463 checklistsJul 15-21: 5.0% of 18642 checklistsJul 22-31: 3.8% of 31215 checklistsAug 1-7: 1.9% of 28163 checklistsAug 8-14: 0.9% of 31329 checklistsAug 15-21: 0.9% of 23878 checklistsAug 22-31: 0.7% of 28508 checklistsSep 1-7: 0.5% of 20878 checklistsSep 8-14: 0.6% of 19671 checklistsSep 15-21: 0.4% of 19859 checklistsSep 22-30: 0.3% of 25179 checklistsOct 1-7: 0.4% of 19420 checklistsOct 8-14: 0.4% of 21925 checklistsOct 15-21: 0.3% of 20995 checklistsOct 22-31: 0.4% of 29258 checklistsNov 1-7: 0.4% of 21269 checklistsNov 8-14: 0.5% of 22753 checklistsNov 15-21: 0.4% of 21982 checklistsNov 22-30: 0.4% of 29475 checklistsDec 1-7: 0.3% of 20810 checklistsDec 8-14: 0.4% of 22229 checklistsDec 15-21: 0.3% of 25148 checklistsDec 22-31: 0.3% 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.

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Where in Arizona

Best counties

Share of checklists at the peak
  1. Santa Cruz CountyBest mid June · 1883 checklists that week, 162,726 in all20%
  2. Cochise CountyBest the second week of June · 3072 checklists that week, 190,093 in all11%
  3. Maricopa CountyBest early July · 2740 checklists that week, 269,896 in all6.6%
  4. Pinal CountyBest late June · 459 checklists that week, 40,036 in all5.9%
  5. Pima CountyBest late June · 6159 checklists that week, 437,722 in all4.8%
  6. Yavapai CountyBest the second week of May · 2442 checklists that week, 83,606 in all2.3%

Best spots

Share of checklists at the peak
  1. Portal (northwest)Cochise County, best late May · 135 checklists that week, 2,872 in all61%
  2. Himmel ParkPima County, best mid May · 29 checklists that week, 2,776 in all52%
  3. Arivaca Lake and LandPima County, best late June · 27 checklists that week, 1,459 in all51%
  4. Madera CanyonSanta Cruz County, best late June · 408 checklists that week, 24,451 in all51%
  5. Northsight ParkMaricopa County, best mid May · 25 checklists that week, 1,219 in all47%

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

Best time of day

In Arizona, the Bronzed Cowbird is most often listed on checklists started between 5 and 7 am (4.4% of those checklists).

0%2%4%6%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: 5.5% of 38350 checklists6 am: 4.0% of 118786 checklists7 am: 2.1% of 183415 checklists8 am: 1.3% of 187346 checklists9 am: 1.1% of 151342 checklists10 am: 1.0% of 124522 checklists11 am: 1.0% of 97088 checklists12 pm: 1.0% of 78110 checklists1 pm: 1.0% of 73059 checklists2 pm: 1.0% of 68912 checklists3 pm: 1.2% of 68060 checklists4 pm: 1.3% of 69387 checklists5 pm: 1.5% of 52951 checklists6 pm: 1.5% 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
January0.3%0.4%0.4%0.3%
February0.3%0.2%0.3%0.3%
March0.3%0.3%0.3%0.4%
April0.6%1.0%1.1%1.8%
May3.4%4.8%6.0%6.6%
June6.0%6.0%6.5%6.4%
July6.2%5.8%5.0%3.8%
August1.9%0.9%0.9%0.7%
September0.5%0.6%0.4%0.3%
October0.4%0.4%0.3%0.4%
November0.4%0.5%0.4%0.4%
December0.3%0.4%0.3%0.3%

Neighboring states

  • New Mexico: arrives late April, 1 week later than Arizona
  • Texas: arrives mid March, 4 weeks earlier than Arizona
  • Louisiana: arrives early April, 2 weeks earlier than Arizona

Common questions

When do Bronzed Cowbirds arrive in Arizona?
Bronzed Cowbirds reach Arizona in mid April, are common by early May, peak in late June (6.4% of checklists), and most are gone by late July.
When do Bronzed Cowbirds leave Arizona?
Most Bronzed Cowbirds have left Arizona by late July, when reports fall below half their usual rate. Stragglers are still reported until the second week of August.
When is the best time to see a Bronzed Cowbird in Arizona?
The Bronzed Cowbird is reported most often in late June, on about 6.4% of Arizona checklists.
Where in Arizona are Bronzed Cowbirds seen most often?
By county, Santa Cruz County, Cochise County, and Maricopa County have the highest peak reporting rates for the Bronzed Cowbird (counties with at least 200 checklists).