Arctic wanderers--Snowy Owl invasion 2013

Snowy Owls are staging an incredible invasion and reports continue to roll in to eBird. Most are coming from Atlantic Canada, the Northeast U.S., and Great Lakes, with several as far south as North Carolina and a pioneering one out to sea on Bermuda! These invasions are thought to occur because of variations in cyclical prey and predator populations in the Arctic, but the exact dynamics still leave many questions. eBird records observations from birdwatchers worldwide and is poised to track this invasion with unparalleled precision. This provides a great opportunity to really understand the dynamics of these poorly understood movements. If you have been lucky enough to see a Snowy Owl this year (or in the past), please submit your sightings to eBird. Suggest that your birding friends do the same! Be sure to treat these birds with respect, and don’t approach too close.

These movements are fascinating and engaging for birders and the general public alike. Biologists and ornithologists have recognized this pattern of periodic incursions of Snowy Owls for centuries. Below is a quick summary of what we know and don’t know about these invasions, and some of the key questions they raise:

• Snowy Owls and other predators have cyclical populations linked to prey abundance. Lemming population cycles likely drive much of the survivorship and breeding success of Snowy Owls. We know Snowy Owls will skip breeding seasons when prey is scarce and may produce large clutches (up to 9 eggs!) when prey is abundant.
• Although lemming scarcity is often implicated in Snowy Owl invasions, a bigger driving force may be highly productive breeding seasons (with multiple young fledged per pair). Periods of summer lemming abundance thus may drive these invasions more than lemming scarcity. The high proportion of first-winter (immature) owls during most invasions provides evidence that high breeding productivity is a major factor in these invasions.
• Snowy Owls are highly mobile. In addition to winter movements, they may move over 1000 km across the Arctic in summer. This is presumably a strategy for the birds to locate areas with abundant rodent prey for their young. In areas where prey is abundant, Snowy Owls may nest in fairly high density, but could be nearly absent when prey is scarce.
• In addition to rodents, Snowy Owls eat lots of birds, especially small waterbirds like ducks and even alcids (e.g., Ancient Murrelets, Dovekies). The role of seabird populations in these invasions is not well understood, but clearly many owls on the Great Lakes and Atlantic coast prey heavily on waterbirds, flying out over the water to hunt them, especially at dusk.
• This year’s invasion, focused on the eastern North America, suggests that breeding conditions may have been excellent in the eastern Arctic this past summer. The southward push we are seeing now might be driven both by Snowy Owls from far and wide that bred in the eastern Arctic, as well as higher than normal numbers of young being fledged. Unfortunately, identifying the age and sex of Snowy Owls is more difficult than is generally realized. Darkest birds are usually young females and the whitest birds usually adult males, it’s especially hard to determine the age and sex of intermediate birds. (Note to eBirders: When possible, take photos and embed them in your checklist (instructions here) to document the owls you see. With visual evidence, you later may be able to get help  determining the age and sex of your owl.

BIRDS AS BELLWETHERS

One of the main goals of eBird is to track bird populations to better understand the world around us. Movements and populations of birds represent a great way to monitor the pulse of ecosystem health. In the 1960s, declines in Peregrine Falcons and Bald Eagles helped to reveal the danger that DDT and other organochlorides were posing to humans and the ecosystem around us. Last year’s Razorbill invasion was an indication of drastic departures of sea surface temperature from historical norms. These owls are surely telling us something, but we still don’t understand exactly what. It could be that this is a large invasion that is part of periodic and natural fluctuations; or an unsettled Arctic environment could be part of the story. eBird is providing a great tool to assimilate the data and compare it to previous movements.

Climate in the Arctic is changing dramatically now, with major losses in sea ice, significant changes in snowfall from historical means, and a general increase in summer temperatures. Warm summers and more variable climate is certainly affecting the ecosystem in ways we are only starting to understand. Here are a couple possible effects on Snowy Owls to consider:

• Although these invasions have been happening for centuries, a warming Arctic is likely to be affecting the exact dynamics. How warmer summers and increased snowfall affect summer lemming cycles, Snowy Owl cycles, winter prey availability, and  complex interactions between these factors is still poorly known.
• The ability of Snowy Owls to hunt waterbirds in the Arctic may be related to extent of sea ice. Snowy Owls that specialize on hunting seabirds could see both benefits and costs to changes in sea ice extent (as waterfowl and seabirds may or may not concentrate near the ice edge and may or may not move south).

WHY DO SNOWY OWLS SHOW UP AT AIRPORTS?

After traveling such a great distance, why do these birds show up at airports? Snowy Owls are birds of open areas and prefer undisturbed beaches, rocky jetties, sand dunes, open marshes, and extensive grasslands. As native grasslands have given way to development, some of the only remaining open habitats are now found at airports. Airports provide the most similar habitat that these owls can find to where they want to be. And it’s not just owls–many grassland species in the Northeast are best found at airports, including Upland Sandpipers, Grasshopper Sparrows, Eastern Meadowlarks, and American Kestrels. All of these are in serious declines.

The controversial killing of Snowy Owls by the New York Port Authority, because of their perceived risk to airplanes, was widely covered in the media. Fortunately, a better model has long been in place at Boston’s Logan Airport, and the practice of trapping and relocating the owls was quickly adopted for New York airports (see article here). We applaud this rapid reconsideration, but it’s only a temporary solution. The underlying problem is the loss of grassland habitat, and along with it the loss of meadowlarks, Short-eared Owls, and pollinators like bees and butterflies.

THE 2013 INVASION

This year’s invasion is one of the most dramatic natural history spectacles in the Northeast and it is a story that continues to unfold. One of the more amazing accounts comes from an observer in northeastern Newfoundland, found 75+ from a single observation point and 206 snowies on a drive down a single road!

eBird is built to help you explore this year’s invasion and compare it to past years. The range maps provide a great place to get started and they can also lead you to some areas where Snowy Owls have been seen in your area. In addition to the below images, be sure to explore the range map links, zoom in for finer detail, and change the years using the toggle on top.

Fig. 1. Snowy Owl point map for Nov-Dec 2013 as of 11 December (view live map online here). Note the concentration on the immediate Atlantic Coast, the exceptional records south to North Carolina and Bermuda, and the relative scarcity in the Great Plains and Pacific Northwest. Note that unlike the images below, this includes just 41 days, rather than the full 61 days!

Fig. 2. Snowy Owl point map for Nov-Dec 2010 (view live map online here). This is probably a below average year, but shows the extreme variability of Snowy Owl occurrence in southern Canada and the Lower 48 states. Many birds probably remained in the north during this winter and it is probable that relatively few young were produced anywhere in the Canadian Arctic.

Fig. 3. Snowy Owl records in Nov-Dec 2011 (view live map online here). Compare this map to the one from 2013 to see just how different this year’s invasion is. While 2011 was the best ever in Kansas, Missouri, and many nearby Great Plains states, the 2013 invasion is producing more records in the Northeast, especially New Jersey, Delaware, Maryland, and Virginia, where the species occurs less than annually. Read more about the 2011 invasion

The eBird signal for the 2011 invasion was helped along by a couple individuals who helped compile records from people who saw Snowy Owls but did not use eBird. We would welcome similar efforts this year. Please encourage your friends and birding companions to enter their records. In 2011 a proxy eBird account was established to collect Snowy Owl records, taking care to submit as Incidental observations and incomplete checklists, while at the same time plotting the birds accurately and giving observer attribution in the species comments. This year, regional compilers could help to better document this year’s invasion by making sure reports from your state or area get entered in eBird. Please coordinate these efforts through your local listserv or birding club.

FINDING SNOWY OWLS

With so many Snowy Owls around, we encourage birders throughout southern Canada, the Northeast, and Great Lakes to get out looking for them. Please submit complete checklists, with or without owls, from your searches.

Check shorelines first and foremost. Snowy Owls are often found on beachfronts, and even piers and buildings along lake edges. They often focus on hunting ducks, coots, alcids and other waterbirds, so places these birds concentrate may help you locate one. Beachfront areas with sand dunes are among the best areas to find them. Extensive marshes, open fields (especially barren hilltop fields), and of course, airports, are other favored areas. Please be careful when checking airports and make sure you view from approved areas and are respectful to any airport security officials. Most Snowy Owls are relatively sedentary during the day, but perk up and hunt at dusk and evenings.

The map link for 2013 will help you find Snowy Owls reported near you. While we encourage you to try to find your own, in some southern areas your chances may be very poor unless you take advantage of the chance to view a bird found by others.

VICARIOUS ENJOYMENT OF SNOWY OWLS

We have created a special *Snowy Owl Alert* in eBird, which shows recent Snowy Owl reports in the Lower 48 U.S. states, including dozens of superb photos. If you haven’t yet connected with a Snowy Owl near you, you can live vicariously through the amazing experiences of others. If you are seeing Snowy Owls, make sure to share the experience with non-birding friends and people you encounter while viewing. Seeing these magical ghostly emissaries from the Arctic is engaging for almost everyone and a great way to get the public excited about birds and the natural world.

Be sure to check out these eBird checklists in particular:

• Video from Tom Johnson of a Snowy Owl defending itself against an aerial assault by Peregrine Falcons.
• A stunning photo shoot at Presqu’Isle in Pennsylvania by Geoff Malosh
• Another great photo shoot, including a bird wheeling out over the ocean, by Ryan Schain
• An amazing Snowy Owl far offshore, photographed by researchers deploying a buoy and entered through a proxy account. Be sure to click the “map” link from the checklist to see were this was!
• Not the best photos, but a distraction while compiling this article. This Snowy Owl wins the award for “closest to the Cornell Lab of Ornithology so far in 2013”. See the daylight photos and others after dark!

VIEW FROM A SAFE DISTANCE

This is a great opportunity to enjoy these Arctic visitors and share one of the world’s most impressive birds with the general public. But we must also stress that these birds should not be approached too closely. Snowy Owls are large and can be enjoyed and photographed from a safe distance. Please do not approach them too closely. Many of these birds are probably food-stressed and need to hunt to maintain their strength. Close approach by birders or photographers could make this much harder for them. Please view these owls from a safe distance and help others to understand how to act appropriately. Please also see our article on reporting sensitive species.

QUESTIONS FOR THE FUTURE

These movements present a great opportunity to analyze the patterns and learn something substantive about these movements. We encourage birders and scientists to think about these questions, download eBird data (all eBird data is free for download via the Explore Data page), and try to make sense of these Snowy Owl patterns. Here are some things we are thinking about:

• Where exactly are these birds coming from? While this question may be hard to answer directly, the patterns of their arrival may yield some insight.
• One key question is how often these birds are arriving directly off the ocean. Several birders have seen owls flying far out over the ocean, including one photographed on an offshore buoy far out to sea. The Bermuda bird clearly crossed a vast ocean. Could some of these birds be flying direct from Greenland, just as many migrant Peregrine Falcons do?
• Can specific dates of the influxes to certain regions be identified? Can we tie those to weather conditions to better understand the arrival of these owls?
• How does this year compare to past years? To compare this year’s invasion to similar movements in the 1960s and 1970s requires some careful consideration of the larger number of birders active today, but some general comparisons can certainly be made and can help to inform us about this year’s movement. This is one of the reasons it is also important to enter complete checklists, even when you don’t see a Snowy Owl.
• How well will the birds survive this year? East Coast museums and wildlife rehabilitators are sure to receive dead or dying Snowy Owls this year, and these data help to reveal how well these birds surviving. Are coastal birds better suited to stay strong than inland ones?

We invite everyone to enjoy this year’s invasion, share it with birders and non-birders alike, view the owls from a safe distance, and use eBird to report your sightings and better understand the movement and the questions above.

Snowy Owl at Stone Harbor Point, NJ, 2 December. Photo by Tom Johnson.

ADDITIONAL RESOURCES

Bruce Mactavish blogs about the Snowy Owl incursion and, with some data from Quebec, is able to opine on the area of high productivity last summer: Bruce’s blog post here.

Satellite tracking of Snowy Owls from Nunavut, Canada: PDF here

Satellite tracking of Snowy Owls from Norway: link here