Friday, March 23, 2012

What does summer in winter mean for birds?

We are in the midst of an unprecedented March heat wave. Here in southeast Michigan, we have experienced a week of temperatures over 70F (and a few over 80F), but this warmth is not a local phenomena. Records are being shattered all over the eastern U.S. and Canada.

The growing season in Michigan is about five weeks ahead of schedule. Many insects are also making very early appearances. That, in a nutshell, is the problem with a stretch of warm weather that comes ahead of the arrival of many migratory birds.

In my previous post, I discussed the migration timing of Neotropical (long-distance) migrants -- those species that winter in the tropics.  As I mentioned there, the annual cycle of migratory birds has been choreographed by evolution to provide maximum resources at all the proper times of year. Birds wintering in the tropics take advantage of the resources available there, and fatten up towards the end of our winter. This enables them to make the journey north, back to their breeding areas in North America. As they move north, they take advantage of the insects that are emerging to feed on the new flush of leaves or opening blossoms on trees and other vegetation. A few short weeks later, they rely on soft-bodied insects such as caterpillars to feed their young. In autumn, the bounty of fruit, seeds, and nuts enables southbound migrants -- many species switch from a diet of insects to a diet dominated by fruit -- to gain and maintain the fat they need to make the long journey back to the tropics for the winter.

Favorable weather patterns can facilitate migratory flights, provided birds are on the move. Since the migratory movements of birds are primarily triggered by photo-period (day length), many long-distance migrants have not yet departed the tropics.

These birds are now already very out-of-sync with the insect resources that they need on their return trip to their nesting grounds. The longer it stays warm, the farther out of sync bugs and birds will be. This mismatch will extend into the nesting season, and could have significant impacts on successful reproduction.

However, it's nearly inevitable that we will see a return to cold weather. As reported by the National Weather Service, the average date of last freeze in southeast Michigan is not until late April.  And based on past years, most of southeast Michigan will have a hard freeze (28 degrees or lower) sometime during April.

Under this scenario, insects will become inactive, and many will simply die. They may perish before they have an opportunity to reproduce, or their eggs or early life stages will not be able to survive. If cold weather persists, it could also kill tender leaves, cause flowers to drop, or kill their pollinators. Migrants arriving during this period, or trying to reproduce afterwards, may experience a severe food shortage. Short-distance migrants such as robins, which have already started nest building, are likely to lose their first brood. These species typically have two or more broods in a season, and so may be able to raise some young later. But long-distance migrants are usually single-brooded, and have only one chance to nest successfully. If they are in poor condition they may not even attempt to nest.

A cold snap could also prevent plants from setting fruit (whether seeds, berries, or nuts). As noted above, these are essential crops for fall migrants, and a lack of resources on fall migration could cause outright mortality or late arrival on the wintering grounds, and consequently lower quality winter territories. In turn, reduced health in winter has carry-over effects that reach into subsequent seasons.

The birds most at risk are the long-distance migrants, particularly forest species. The Boreal Songbird Initiative has an excellent, referenced page dedicated to the effects of global warming on birds. For an example of research on how mismatches between food requirements and food availability impact long-distance migrants, see this paper: Avian population consequences of climate change are most severe for long-distance migrants in seasonal habitats. While this warm spell is a weather event, it is indicative of the problems associated with a changing climate.

Here in spring 2012, things are already seriously out of whack. At this point, the best we can hope for is a return to much cooler weather, but without hard freezes or measurable snowfall.

Update:  Only four days later, we have had a freeze in southeast Michigan. Meteorologist Jeff Masters notes that it probably caused tens of millions of dollars of damage to Michigan fruit crops. Fortunately, it was only a single night, but we have a couple of months yet to go. Masters also lists other significant freezes -- including the one in 2007 which occurred in April. This preceded one of our poorest fall banding seasons, and I also discussed it in my summary of the spring 2008 survey season.

Thursday, March 22, 2012

Early Neotropical migrants (?)

With the exceptionally warm weather this March, I have been seeing quite a few reports of early migrants. I'm not too surprised to see early reports of species that winter in the U.S. (short-distance migrants). This is probably due to both favorable weather and the fact many more people are outdoors this year looking for birds. But reports of Neotropical (long-distance migrants) deserve more scrutiny. What follows is a version of a message I sent to our local birding listserv.

What are we to make of reports of Neotropical migrants arriving many weeks ahead of schedule? Why would these birds, wintering in the tropics with no "knowledge" of an early spring here, be arriving so early? The migratory movements of these birds are typically triggered by photoperiod.

For a Wood Thrush, for example, to be present in Michigan right now means that it departed its Central American wintering grounds in mid-February. Recent studies have indicated Wood Thrushes take about a month get here. The average arrival date here in southeast Michigan (based on 16 years of data) is May 1, so the typical departure from Central America is early April. While favorable weather patterns can accelerate migratory flights, the birds have to be on the move to begin with.

There are many things we still don't know about the interactions of weather, climate, and birds. Yet it seems hard to conceive why so many individuals of various species (and for us to find even a handful having survived to arrive in Michigan, the starting number would have to be larger) would begin migrating so prematurely. The annual cycle of birds has been intricately choreographed through evolutionary time. Remember, these birds have to spend a period of time (also coincident with resources in the tropics) gaining weight in order to migrate north, just like they do to go south in fall.

While the data is not infallible, an excellent assessment of where migrants are currently being located can be found at eBird. Go to Explore Data, Range and Point Maps, choose a species, and specify March to March, current year (direct link here). There have been only five reports of Wood Thrushes in the U.S. so far this month. Most are still in Central America.

I suspect that some (most?) of the Neotropical migrants being reported at northern latitudes, if accurate, may actually be birds that did not migrate last fall and managed to survive the very mild winter. Black-throated Green Warbler and its close relatives, orioles, and tanagers, for instance, are occasionally reported in winter. I've also given some thought to the fact that every year there may be a few exceptionally early migrants which routinely do not survive jumping the gun that might be having more luck this year. Still, this is probably pretty rare and might be more applicable to short-distance migrants.

At any rate, just because it's warm outside doesn't mean we can expect birds too many weeks ahead of  schedule. When they do arrive, detection and viewing this year will be greatly diminished by leaves -- this is a good year to learn your bird songs!

Update: Marshall Iliff, one of the eBird coordinators at Cornell, has written a couple of long but excellent posts on the Massachusetts bird list regarding early arrivals, including hummingbirds. He's someone who has a vast experience in examining migration patterns through his work. I strongly encourage you to at least read through this one. An earlier post deals more with common early migrant ID problems.

Friday, February 24, 2012

Winter Bird Population Survey 2011-2012

The 20th year of RRBO's Winter Bird Population Survey has been completed. Over the 20 December to 20 February survey period, 39 species were tallied. The previous annual average number of species is 38. We added two species this year. The first was Gray Catbird. I had two on the first count day, 20 December 2011. I was standing and looking at one while I heard another calling. We have only one previous winter record of catbird in Dearborn, and none from campus, so this was quite notable. Single catbirds were reported by other observers several times over the winter. The final observation was by me on 27 January 2012 -- and the bird I saw that day was banded. The bird I was looking at on 20 December was not, and other observers didn't look for bands.

The other new species was a Pine Warbler was visiting the EIC suet feeders on 26 December. This was the second Dearborn and first campus winter record. This brings our cumulative total over the years to 72 species. It's amazing that after 20 years, new species can still be added to this count, but in fact we have added at least one new species every year except 2006-2007. Here is a quick-and-dirty graph of the accumulation of species.


I always check all the tangles along my route, and this year was rewarded twice with a Northern Saw-whet Owl. This may have been one or two birds, as the spots were different. I suspect it (they?) was just passing through, as I looked in the same spots every time, but it was only present in late January.

As for misses, Cedar Waxwing was not seen this year, only the fourth year it has been missed over 20 years. Although Pine Siskins and Common Redpolls were recorded several times over the period elsewhere in Dearborn, we did not have any sightings on campus.

American Crow in this immediate area continues to be nearly absent. You can look at last year's post for the story of the precipitous decline and lack of recovery since West Nile Virus (WNV) entered our region. This year I had a single crow fly over on three occasions, all in February when they begin to move around a bit. 

There have been 21 species that have been recorded all 20 years on the WBPS, listed below. Those in italics have also been recorded on over 95% of the 278 individual surveys completed over those years: 

Canada Goose, Mallard, Red-tailed Hawk, Mourning Dove, Red-bellied Woodpecker, Downy Woodpecker, Hairy Woodpecker, Northern Flicker, Blue Jay, American Crow, Black-capped Chickadee (missed on only a single survey in 20 years), White-breasted Nuthatch, Brown Creeper, American Robin, European Starling, American Tree Sparrow, Dark-eyed Junco, Northern Cardinal, House Finch, American Goldfinch, and House Sparrow.

Let's return to the American Crow again. Although Crows were recorded every year, prior to West Nile Virus, they were recorded on nearly every survey -- in the years 1993-2002, they were present on 97.4% of the surveys. In the years 2003-2012, they have been present on only 24.8% of the surveys. A couple of years, I only recorded them on one day.

This tidbit shows the value of this type of long-term data set for monitoring resident birds. It's critical to have programs like this in place, ready to provide "before" data when some unanticipated natural event occurs, including disease, or to see how bird populations respond to more gradual environmental changes.

So while the crow situation is very sad, it has provided me with motivation to get out there and count. One thing you need to know...I hate being out in cold weather. Of these 278 surveys, probably 270 were awfully routine. But the analyzed results will be worth even more than the sum of all the parts, and I'll be working on a complete summary of the Winter Bird Population Survey now that 20 years have been completed.

On the RRBO web site, you can find the full results of all 20 years of surveys, along with information on the protocol.

Tuesday, January 17, 2012

RRBO is 20 years old!

The Rouge River Bird Observatory banded its first bird -- a Black-capped Chickadee -- in 1992. Since then, we've banded over 33,000 more birds, conducted thousands of bird surveys, compiled hundreds of thousands of bird records, participated in numerous cooperative research projects, trained dozens of field volunteers...our list of accomplishments goes on.

For our 20th anniversary, we'll be starting an email newsletter to share a look back at some highlights of the past twenty years, and look forward to our future. If we don't have your email address, please sign up for our newsletter at this link. I'll be putting out our first issue later this month.

We thought it might be fun to spruce up the RRBO logo to reflect our anniversary. The original depiction of the bird with two leaves is from an architectural detail in Fair Lane, Henry Ford's estate; we chose it to reflect the historic nature of our study site. You may see this little bird carrying a banner acknowledging RRBO's 20 years of bird conservation. It will certainly be sitting on a branch that now has three leaves, representing our growth and the start of our third decade.

Given that RRBO is donor-supported, all our successes have been yours as well. We can all celebrate together!

Wednesday, January 4, 2012

Dearborn portion of the Detroit River CBC, 2012

The Detroit River Michigan-Ontario Christmas Bird Count was held, as it is each year, on January 1. This was the 35th year for the count, which is centered at I-94 and Warren Ave, and the 18th year that RRBO has coordinated the field work in the city of Dearborn.

The day began with mild temperatures which had been the hallmark of the autumn and winter season up to that point. All water was open, and there was (and had been for the most part) no snow cover. Waterfowl and seed-eating birds were dispersed far and wide. We'd seen an excellent fruit crop in late summer and fall, but most had been stripped by the time New Year's Day arrived.

We ended the day with 39 species, well below the average of 46 because the party covering the Ford Rouge Plant was denied access this year (not by Ford, but by the private security firm of another company). Thus, we missed a number of species of waterfowl and the two dozen or so Black-crowned Night-herons that typically roost in a small pond on the property.

Nonetheless, the day was not without highlights. Covering the UM-Dearborn campus, Greg Norwood found one of the Gray Catbirds first found on 20 December. This is a new species for the Dearborn portion of the count and brings the cumulative total to 87. A Sharp-shinned Hawk seen on 29 December couldn't be located, but is tallied as a "count week" species and is also new for the count. Greg also found the Yellow-bellied Sapsucker that has been hanging around for weeks. This is only the second time sapsucker has been found on the Dearborn portion of the count.

Darrin O'Brien and I covered the various plantings on Ford properties. Like last year, most of the seed-eating birds were found at the fields in front of Ford World Headquarters. Most numerous were House Finches (over 900) and House Sparrows (over 1800). The day's total of 1038 House Finches was a new high for the count. Many of the fields had a lot of standing water, making it harder for the little birds that like to forage on the ground. The total of 26 American Tree Sparrows was a new count low. Also present at Ford HQ was a Peregrine Falcon. It chased around a Red-tailed Hawk before landing on the Ford building.

Arrow points to grooming Peregrine.

Cathy Carroll turned up 18 Great Blue Herons along the concrete channel of the Rouge. Often this group of birds roosts along the river on campus, but forages all along the river. She also saw one of the seven American Kestrels in the city, which is a new high for the count.

Finally, only one American Crow was found all day. This is a new low, and represents a decade of counts with fewer than 20 crows (most years fewer than ten). The local population has simply not recovered from West Nile virus, and I am beginning to wonder if I will ever see new birds move in.