Bird Deaths in Carson

Left: Orange-crowned Warbler Leiothlypis celata by Dawn Beattie (CC BY-2.0). Right: Wilson’s Warbler Cardellina pusilla by Tom Benson (CC BY-NP-2.0). These are the two most commonly seen warblers during fall migration around Carson.

Posted by Paul Green, updated Wednesday September 23, 2020.

October 18, 2020. A recent update and overview can be found here: Dying birds and the fires: scientists work to unravel a great mystery

Many in Carson are commenting on large numbers of dead “small, yellow birds” following the cold front that moved over us overnight on Tuesday, 8 September, 2020, depositing snow around Carson.

In the days before the cold front arrived, the first week of September 2020, there was a build-up of warblers in our community, mainly Wilson’s Warbler, Orange-crowned Warbler, and MacGillivray’s Warbler.

These birds are currently on a medium and long-distance migration to their wintering grounds in central America. MacGillivray’s Warbler breeds as far north as Alaska, down to the southern Rockies in New Mexico. Wilson’s Warbler is much more northerly, breeding across the extreme north of the North American continent, with some breeding in the Rockies as far south as New Mexico. Orange-crowned Warbler breeds across Canada, and the north western United States and further south along the Rockies.

All species are migrating south this time of year to spend their winter in places that can support their insect-feeding habit. Orange-crowned Warblers spend their winter in the coastal south and western United States, and as far south as Belize and Guatemala.  Wilson’s and MacGillivray’s travel as far south as Mexico and Panama. Read more about fall bird migration here.

Left: Townsend’s Warbler Setophaga townsendi by Mike’s Birds (CC BY-SA-2.0). Right MacGillivray’s Warbler Geothlypis tolmiei by Alan Schmierer (CC0 1.0). These two species are frequently seen during fall migration in Carson.

Our local resident, non-migratory birds, such as the White-breated Nuthatch, Juniper Titmouse, and Mountain Chickadee, all seem to be unaffected by this die off.

Birds typically get behind cold fronts for their migration, flying with the wind of the high pressure that develops behind them. What may have happened in this case is that the birds waited for the cold front to pass, but as a result suffered the consequences of the falling temperatures. However, there appear to be additional processes at work, perhaps related to the west coast forest fires.

The birds that were here in the days before Tuesday September 8 were feeding frantically on insects on vegetation. If you have green, leafy vegetation in your garden you may have seen the birds searching the plants for any insects they could find. Good news for gardeners!

Carson on September 9th, 2020.

Back to those additional processes: over the last few weeks large numbers of dead migratory birds, of a wide range of species, were found in southern New Mexico, and that event is still under investigation. There is a suggestion that the fires on the west coast may have had some impact on the birds, perhaps by forcing them to leave for migration before they were ready. Birds need to build up significant reserves of fat and protein before they set off. They may also have suffered as a result of flying through the smoky air. Ornithologists are working on these questions, and you can help them find the answers (see below for information).

It’s possible that, for those birds which were suffering as a result of the fires in the west, and were very low on fuel reserves when they arrived, the snow and cold weather of the night of 8 September was the final straw. They may not have had the energy reserves to survive a night of snow and plummeting temperatures, followed by two more days and nights of low temperatures on September 10 and 11, 2020.

As of September 22, 2020, in the south of New Mexico, scientists have seen mortalities in both insectivores and seedeaters. About one third of the 400 specimens reported are sparrows, very different from the situation in Carson. While new mortalities in Carson appear to have stopped after September 11, 2020, a small number are still occurring in the south up to September 22.

Warblers and other migrants continue to pass through Carson throughout September. Some people have asked what they can do to help the birds. As insect eaters, you can’t help them with food (except by planting for them for next year: leafy herbaceous plants, such as sunflowers and native herbs, and deciduous trees like NM Locust, Aspen, Cottonwood are good). Essentially the birds that visit us are exhausted from long-distance flying and have used up their food stores. The best thing you can do for them is not to stress them and leave them alone to feed. Keep your dogs and cats away from them: in their weakened state the birds are easy prey. Left alone to feed for a few days they will gain the strength to fly on and make it safely to their wintering grounds.

And bigger picture you can help ornithologists who are trying to solve this mystery. First, you can report any dead birds you see through the iNaturalist website and app. The project is called the Southwest Avian Mortality Project. Take a photo and send it to them. Instructions are below. This would make a great project for home schoolers. Introducing them to the iNaturalist site will be a great eye-opener to the many forms of wildlife around them.

We can expect more migrants passing through. You can see when future nights of high migration can be expected in Carson at the BirdCast website. Typically, the morning following a night of high migration you’ll see a lot more migrant birds outside your house in the morning. So that’s a good time to go out and check for dead birds.

Another way you can help scientists understand more about the causes of this mass mortality is to save any birds you find for analysis. Instructions for how to handle the dead birds are below.

I’d welcome your observations, comments, or questions at [email protected] If you are interested but unable to navigate the iNaturalist site, send me your photo together with the date and location of where the bird was found and I will post it to the iNaturalist site on your behalf. Thank you!

Read more about the death of birds in the southwest this fall at these sites:

Cornell Lab of Ornithology

National Audubon

American Birding Association

Here’s a link to an interview on September 15th by Martha Desmond, Professor in the Department of Fish, Wildlife and Conservation Ecology, New Mexico State University

How to share your observations related to recent avian mortalities using the iNaturalist APP.

We are interested in observations and/or photos

  1. Download the free app from your app store (or visit the website @ ).
  2. Open the app.
  3. Touch the camera icon.
  4. Take a photo (or select a photo from your photo library, or decide to just make a text observation).
  5. Fill in whatever details you want to add. Your smart phone will know where and when you are and fill in those details automatically (unless you’re on a WiFi-only tablet like many iPads, in which case you’ll need to put a pin on the map).
  6. Touch the Save button.
  7. Touch Upload.
  8. Add your observations to the “Southwest Avian Mortality Project”. Keep in mind that you can add multiple photos to one observation. Just touch the camera icon again to add another photo. It’s quite handy to take an assortment of photos of the different features you see to help someone else ID it, or confirm your ID. If your critter is small or far away, note the trick of holding your smart phone camera up to a magnifying glass or a pair of binoculars.
  9. Here are some helpful links for new iNaturalist users to learn how to submit an observation.
    iNaturalist Getting Started Guide has some simple instructions for how to submit an observation:
    And some tutorial videos for mobile app and web uploader:

How to collect a specimen for analysis

  1. Please use exam gloves or cover your hand with a baggie to avoid contact with the carcass & wash hands thoroughly afterwards
  2. Collect specimens in plastic baggies & include a paper note inside the bag with the date, location, & species identification (if known).
  3. Tally the number of specimens collected per site – this will be used in our submission report to the National Wildlife Health Center.
  4. Double bag the specimen & store it in the freezer.
  5. Send reports of specimens collected to [email protected]
  6. Erin will later contact you to advise where to send your specimens, and when.


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