WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Maryland?

Adult female Brown-headed Cowbird
Photo: Nicole, CC BY 4.0 via iNaturalist

Brown-headed Cowbirds are in Maryland all year, but most are here in spring: numbers build from late March, peak in late April (36% of checklists), and fall back by early July. In the quietest week (mid December) they are still on about 2.8% of checklists.

When to look

Numbers buildMar 22-31late March
PeakApr 22-30late April
Fall back byJul 1-7early July
FewestDec 15-21mid December

Best: late April. Here all year; numbers build from late March and fall back by early July. Peak: on about 36% of Maryland checklists.

  1. Janrare
  2. Febuncommon
  3. Marcommon
  4. Aprpeak season
  5. Maypeak season
  6. Junpeak season
  7. Julcommon
  8. Auguncommon
  9. Seprare
  10. Octuncommon
  11. Novrare
  12. Decrare

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

0%10%20%30%40%Jan 1-7: 3.2% of 28716 checklistsJan 8-14: 3.8% of 21449 checklistsJan 15-21: 4.3% of 21267 checklistsJan 22-31: 4.7% of 29144 checklistsFeb 1-7: 4.8% of 21347 checklistsFeb 8-14: 6.8% of 22166 checklistsFeb 15-21: 6.7% of 29986 checklistsFeb 22-28: 6.6% of 22427 checklistsMar 1-7: 8.7% of 21389 checklistsMar 8-14: 12% of 22192 checklistsMar 15-21: 16% of 22823 checklistsMar 22-31: 22% of 33720 checklistsApr 1-7: 28% of 25513 checklistsApr 8-14: 31% of 27718 checklistsApr 15-21: 36% of 29328 checklistsApr 22-30: 37% of 42595 checklistsMay 1-7: 35% of 38532 checklistsMay 8-14: 33% of 42722 checklistsMay 15-21: 33% of 31936 checklistsMay 22-31: 30% of 36903 checklistsJun 1-7: 28% of 23191 checklistsJun 8-14: 26% of 21853 checklistsJun 15-21: 25% of 21000 checklistsJun 22-30: 23% of 25133 checklistsJul 1-7: 21% of 18715 checklistsJul 8-14: 17% of 16376 checklistsJul 15-21: 13% of 15793 checklistsJul 22-31: 9.1% of 21969 checklistsAug 1-7: 7.6% of 16013 checklistsAug 8-14: 7.1% of 15249 checklistsAug 15-21: 6.5% of 15674 checklistsAug 22-31: 6.6% of 24925 checklistsSep 1-7: 4.9% of 19808 checklistsSep 8-14: 3.6% of 18513 checklistsSep 15-21: 3.9% of 21901 checklistsSep 22-30: 4.5% of 22901 checklistsOct 1-7: 5.6% of 19111 checklistsOct 8-14: 5.5% of 18482 checklistsOct 15-21: 5.9% of 17380 checklistsOct 22-31: 4.8% of 23992 checklistsNov 1-7: 3.9% of 17915 checklistsNov 8-14: 3.4% of 18905 checklistsNov 15-21: 3.5% of 16259 checklistsNov 22-30: 3.3% of 22852 checklistsDec 1-7: 2.7% of 16108 checklistsDec 8-14: 2.8% of 16512 checklistsDec 15-21: 3.1% of 18952 checklistsDec 22-31: 2.6% of 29728 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 Maryland 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 Maryland

Best counties

Share of checklists at the peak
  1. Queen Anne's CountyBest mid April · 566 checklists that week, 26,875 in all48%
  2. Prince George's CountyBest late April · 3254 checklists that week, 87,907 in all44%
  3. Carroll CountyBest late April · 1073 checklists that week, 26,728 in all43%
  4. Harford CountyBest the second week of May · 1584 checklists that week, 39,311 in all41%
  5. Charles CountyBest the second week of June · 267 checklists that week, 10,064 in all41%
  6. Washington CountyBest late April · 899 checklists that week, 24,020 in all40%

Best spots

Share of checklists at the peak
  1. Fort Washington ParkPrince George's County, best late April · 23 checklists that week, 628 in all88%
  2. Sedgewick CoveQueen Anne's County, best mid April · 64 checklists that week, 3,164 in all88%
  3. Layhill VillageMontgomery County, best the second week of May · 28 checklists that week, 1,211 in all86%

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

Best time of day

In Maryland, the Brown-headed Cowbird is most often listed on checklists started between 6 and 8 am (25% of those checklists).

0%10%20%30%12 am: too few checklists (486) to judge1 am: too few checklists (451) to judge2 am: too few checklists (447) to judge3 am: too few checklists (766) to judge4 am: too few checklists (2076) to judge5 am: too few checklists (11098) to judge6 am: 29% of 56604 checklists7 am: 23% of 139255 checklists8 am: 19% of 148626 checklists9 am: 16% of 126820 checklists10 am: 13% of 106973 checklists11 am: 11% of 87483 checklists12 pm: 9.9% of 74808 checklists1 pm: 9.2% of 69428 checklists2 pm: 8.7% of 67800 checklists3 pm: 8.8% of 67688 checklists4 pm: 9.6% of 60927 checklists5 pm: 12% of 43876 checklists6 pm: 13% of 32930 checklists7 pm: too few checklists (19051) to judge8 pm: too few checklists (5708) to judge9 pm: too few checklists (1977) to judge10 pm: too few checklists (1170) to judge11 pm: too few checklists (635) 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
January3.2%3.8%4.3%4.7%
February4.8%6.8%6.7%6.6%
March8.7%12%16%22%
April28%31%36%37%
May35%33%33%30%
June28%26%25%23%
July21%17%13%9.1%
August7.6%7.1%6.5%6.6%
September4.9%3.6%3.9%4.5%
October5.6%5.5%5.9%4.8%
November3.9%3.4%3.5%3.3%
December2.7%2.8%3.1%2.6%

Neighboring states

  • District of Columbia: arrives late February, 4 weeks earlier than Maryland
  • Delaware: arrives late March, in the same week than Maryland
  • Virginia: arrives late March, in the same week than Maryland
  • Pennsylvania: arrives the second week of February, 6 weeks earlier than Maryland

Common questions

When do Brown-headed Cowbirds arrive in Maryland?
Brown-headed Cowbirds are in Maryland all year, but most are here in spring: numbers build from late March, peak in late April (36% of checklists), and fall back by early July. In the quietest week (mid December) they are still on about 2.8% of checklists.
When do Brown-headed Cowbirds leave Maryland?
Brown-headed Cowbirds never fully leave Maryland: numbers fall back below half their usual rate by early July, but some are still reported in every week, about 2.8% of checklists at the low.
When is the best time to see a Brown-headed Cowbird in Maryland?
The Brown-headed Cowbird is reported most often in late April, on about 36% of Maryland checklists.
Where in Maryland are Brown-headed Cowbirds seen most often?
By county, Queen Anne's County, Prince George's County, and Carroll County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).