I love spectacles of migration, huge numbers of animals moving; no photos can do it justice. I have been lucky to have had the opportunity to see some of these amazing sights. Hundreds of thousands of Sooty Shearwaters off the California coast, thousands of warblers passing by Higbee Dike at Cape May, and tens of thousands of swallows along the Colorado River. Most of us know about the first two spectacles, but what about the third? The sight of thousands of swallows, a giant ball seeming to ebb and flow and then suddenly cascading from the sky into a marsh, must be one of the most amazing wonders of the world.

A lone Tree Swallow in Tillamook Oregon 17 May 2009, beautiful even when not in a huge flock. Copyright (c) 2013 David Vander Pluym

Though it has been known for a long time that large numbers of swallows move through the LCRV (the high count in Rosenberg, et al 1991 being 750,000!), recent years have brought a renewed attention to the spectacle from both birders and ornithologists.
Lauren wrote a bit about our viewing experiences with the swallows last year, where we were able to witness tens of thousands at Martinez Lake.  Even more amazing was the sight of an estimated 1.2 million swallows on 8 May 2011 over Mittry Lake reported in the AZFO seasonal report. I cannot even imagine what that must have been like!

It is likely that a large portion of the western populations of Tree Swallows use the LCRV during spring migration. Not surprisingly, biologists have also been looking into the use of the LCRV by Tree Swallows. In other regions, such as California’s Central Valley, researchers were able to use radar to find where large numbers of Tree Swallows were. This can help to identify areas that are important for staging swallows as well as getting population estimates. An interesting paper on this can be found here.  This link references a talk given that indicated that attempts in the mid 2000’s to find roosts using radar out of Yuma failed. Unfortunately the link to the reference was dead and as of this posting I was unable to find more information on these attempts. However in the past few years attempts were renewed to track Tree Swallow migration by radar out of Yuma by the Arizona Department of Game and Fish and a poster was presented on this at last year’s AZFO meeting. If you missed the meeting you can read the abstract to the poster here. This use of radar to track migrants is an interesting field and has the potential to greatly increase our understanding of migration. Radar can also be helpful to birders as you can check radar stations to see if large numbers of birds are on the move in your area. For those interested in using radar, check out this video tutorial for more information and if you want to try it yourself you can check out this page to view radar.

Barn Swallows (here 23 July 2009 at Malheur NWR Oregon) occur in the thousands in the LCRV in fall, but as yet we have not seen them form the spectacular roosting flocks that Tree Swallows form in the spring. Copyright (c) 2013 David Vander Pluym

Here in the LCRV, the Cliff Swallows are back and building nests, Violet-green Swallows are starting to move and today while trail clearing every time I looked up I would see a steady stream of Tree Swallows flying over. Clearly it is swallow season! Many people wonder when is the best time to see the swallows. There is no way to say for sure if your visit will produce hundreds of swallows or tens of thousands or even a million swallows, but you can maximize your chances by being there at the right time. Though fall can produce good numbers of swallows of multiple species (Barn and Tree can move in the hundreds or even thousands), the real spectacle is the Tree Swallows moving through in spring. The peak time for Tree Swallows is mid March to late April. However as hundreds winter on Lake Havasu and around Martinez Lake, good numbers can be seen in late February and by early March migration is under way. Formerly only a few stragglers would occur into May in the past, however in 2011 the highest known count for the LCRV occurred on 8 May when 1.2 million were estimated at Mittry Lake. At this time it is unknown if this is a regular occurrence or was just a rare occurrence  as it was a cold wet year and a lot of birds moved through later than average. In recent years it is not unusual to have groups of several hundred into early May. During the evenings the swallows swarm and flow and then fall into the marsh in a spiral. This is typically done in the evenings right around sunset, but the timing can vary so get there early and be prepared to wait until dark watching the swallows. It can be a good idea to bring lawn chairs, scope, and insect repellent as you are at a marsh! Be sure and scan with your binoculars over the marsh as the swallow flocks may be distant as well as high up.

Violet-green Swallows are primarily a migrant in the LCRV and most of those that occur are the widespread nominate subspecies thalassina (such as this bird here in Tillamook Oregon 1 Jun 2009). However there is a small breeding population in the Bill Williams River NWR and along the Parker Strip, though there are no specimens they are believed to be an intergrade population between the nominate subspecies and brachypetera which breeds in Mexico. Copyright (c) 2013 David Vander Pluym

Finally, where can you view these roosts? Below I have screenshots of google maps to areas that I have found to be good places to view along with more information on them. They are arranged from south to north. It should be noted that calm conditions are usually better for viewing.

Mittry Lake: I haven’t visited this site for the swallow migration, but 1.2 million! Tree Swallows were estimated from here 8 May 2011. I also don’t know if they were roosting or feeding over it. More details on birding this site can be found here.

Martinez Lake area: Perhaps the best spot in the LCRV is Fisher’s Landing and Martinez Lake. This location is also all around good birding so be sure and get there early so you can scan the lake or check out Imperial NWR. Rarities are always possible and both Brown and Blue-footed Boobies have been found here! To get to this spot from highway 95 north of Yuma turn left onto Martinez Lake Rd. Follow it toward Fisher’s Landing, but just before you get there turn right onto Red Cloud Mine Rd toward the Imperial NWR and Martinez Lake. Next turn left onto Joe Young Dr and park before the buildings where you can overlook the marsh and wait for the swallows. Be sure and listen for Black Rails as well!

An overview of both Ferguson and Martinez Lakes. Ferguson is rarely visited as it is down a long dusty road with lots of private property around it. Swallows may roost there but overall Martinez Lake offers better views and is easier to get to. The blue marker represents a good place to view from. See also the next map.

From the road to Fisher’s Landing, right before entering the landing proper turn right onto the Red Cloud Mine Rd/Wildlife Refuge Rd and then a left on Joe Young Rd. Park off the road at the edge of the marsh where the blue marker is. This has been our best viewpoint for watching the swallows and be sure and listen for Black Rails!

Ferguson Lake likely has swallow roosts, but I have not been there at dusk to find out. It is a long and dusty road coming out of Bard California and is rarely visited (though it has the potential for rarities; for example Lauren Harter and I found a Red-throated Loon there in Dec 2010 and others chasing the loon found a Gilded Flicker). There is also a lot of private property around the lake so if you go it is a good idea to scout out the best place to view it without trespassing. Coming from Laguna Dam you head north on Imperial/Laguna Dam Rd (the name changes depending on what stretch you are on), and turning left onto the first turn for Senator Wash Rd and then make a left onto Ferguson Rd following it to the lake. You can also sort of see if they are roosting there with a scope from Martinez Lake.

Cibola Lake, Cibola NWR:

Following the levee south toward Cibola Lake, at the south end there is a road up the hill for an overview of the lake. This is a great spot to watch the river of swallows at dawn moving north off their roost sites. Check out the Cibola NWR for more info on how to get here.

Blythe area and the Parker Valley: The next day after viewing the swallows coming into roost or that morning after viewing them leaving a roost you might want to take a spin through the Blythe area or the Parker Valley and watch the swallows foraging. Though you want see a single concentration of swallows they can be everywhere feeding and it is a good chance for something rare. I picked Mangrove Swallow as a next ten for Arizona and it would be on my top ten list for California if I did one. To watch the swallows feeding just following any road through the agriculture areas.

Bill Williams Delta: Viewing from the NWR HQ you can often see good numbers of swallows descending into the marshes. However most recent counts here have been in the neighborhood of 20000, still spectacular, but not the numbers seen elsewhere. Good place to view in windy conditions as it is somewhat protected.

North end of Lake Havasu: Viewing from Cape Havasu can produce amazing numbers (I have seen up to 100000 Tree Swallows dropping into the marsh). The problem with this spot is that the swallows are usually distant and a scope is very helpful. There are points that are closer both on the California and the Arizona side, however I have not actually been to these sites to see how the view is for the swallows. They are worth checking out and I hope to be there this spring to check it out. Castle Rock on the Arizona side and north of Havasu Landing on the California side take you much closer to the marshes and probably give you better views. To access Castle Rock go north of Cape Havasu along London Bridge Road and north of Desert Hills make a left on Crystal Beach Rd. Follow this to the end and at the end of the road head left to the end of this road, park and walk through the gate and out onto the bluffs. From here you have a good view of a wide area of marshes. For Havasu Landing you have to access from the California, heading north from Havasu Landing you have to find access between private property, be sure and scout it out well in advance. UPDATE: 16 Mar 2013 The swallows were landing in the southeast most reed island and were easily visible from Cape Havasu and would not have been visible from Castle Rock or the northern most part of Havasu Landing. The area off Sunset Trail north of Havasu Landing may however have given good views. Again be aware of private property. Castle Rock and the northern portion of Havasu landing would be good places for watching the dawn fly out.

Castle Rock is the blue pin on the east side of the river while one of the possible access points for Havasu Landing is on the west side. See text for details.

Havasu NWR and north: the previous high count of 750000 was during a traveling count over part of the Mohave Valley north to Bullhead City of foraging swallows, obviously foraging swallows can be anywhere!

Hopefully this will help people time their trip to the LCRV to see the swallows and help to direct you to the best site. It is a spectacular sight!

-DVP

Literature Cited:
Rosenberg, K.V., et al. 1991. Birds of the lower Colorado River Valley. The University of Arizona Press, Tuscon, Az.