Wednesday, June 27, 2012

Spring 2012 survey results

(Cross-posted at RRBO web site) The spring 2012 survey season took place 3 April through 4 June. On campus, regular surveys were conducted on 58 of the 65 days; some coverage late in the season was truncated due to field work related to our catbird study. Because of the unusual weather (discussed below), surveys were also conducted on 21 days in March.

Excluding March, the campus surveys recorded 124 species (another 19 were recorded in Dearborn off-campus). This is lower than the previous ten-year average of 130 species. The peak day was 3 May with 79 species. This is a similar to our usual peak day total of 80 species, but usually the peak occurs much later in the month (around May 16-20). Both the low species totals and early peak are at least in part attributable to the extremely early leaf-out, which made visual detection of mid- and late-season migrants much more difficult.

This leaf-out -- in which leaf and flower phenology was some five weeks ahead of schedule by April -- was due to the unprecedented hot weather in March. The National Weather Service characterized March 2012 as the warmest on record and the most unusual month in Detroit's history. The average temperature for March was 50.7 F, an incredible 15.6 degrees above the 1874-2011 mean average of 35.1F! Fortunately, the weather did cool down, with April temps right at normal, but May was the 3rd warmest on record. Thus, spring 2012 finished the warmest in southeast Michigan history.

Generally, warm periods in spring that accelerate plant growth also prompt early emergence of insects. This can result in a mis-match between insect resources and the timing of bird migration, especially for birds that are coming from wintering grounds in the tropics. These birds are prompted to migrate by changes in day length, and do not "know" that spring is advanced in the north. The same weather systems that bring warmth to the north may push migrants which have already arrived in the United States northward a little faster. This year, long-distance migrants that had yet to arrive during the early part of the season arrived right about their usual time (see Arrival dates, below).

There were some real concerns that had the hot weather continued, things would have gotten seriously out-of-whack -- you can read my blog post What does summer in winter mean for birds? for a discussion of potential ramifications. Fortunately, cooler weather in April slowed phenology down a bit. While we did have freezing overnight temperatures after the March hot spell, they did not last for many hours in the Detroit area, so insect life was not seriously diminished and it appears that migrants were able to find adequate food resources.

Spring 2012 was also quite dry...especially when compared to last year! In 2011, the precipitation total for Detroit from March through May was over 14 inches. This spring, it was less than half of that, with both April and May having below-average moisture.

While migrants dodged a resource bullet, it seems this combination of advanced plant and insect phenology and dry conditions is likely to have had some impact on breeding birds. This probably depends on how reliant various birds are on particular stages or species of insects as well as the impact weather may have had on a very small landscape scale at locations where birds nested. Perhaps we will detect some changes in the ratio of young to adult birds during fall banding that may shed some light on this. Finally, because they flowered early and pollinators were out and about, many fruiting plants also set fruit early. Fruit is a critical part of the diet of many fall migrants; we'll see if there are any changes in what birds are eating this fall.

Many of the less-common migrants we have come to expect on a nearly annual basis were not recorded this year. This includes Golden-winged Warbler, Prothonotary Warbler, Kentucky Warbler, and Summer Tanager. Acadian and Olive-sided Flycatchers and Philadelphia Vireo were also missed. The most interesting highlight was the number of White-eyed Vireo sightings: five from mid-April to mid-May. Leaf-out was so advanced by mid-May, that many birds, especially non-singing females, may have gone undetected.

I'll add a lowlight on a species I follow and mention frequently: American Crow. Of the 61 days in April and May, crows were recorded in the entire city of Dearborn on only 15 days. Reports were always of one or two birds. Crows were seen more often in March, as observations include migrating birds. In March, crows were reported on 14 days, mostly in ones or twos, with a high number of 11 birds in a flock on 13 March.

Arrival dates
The March hot spell created a flood of reports of early migrants. Many of these are probably best viewed with caution (see my post Early Neotropical migrants for more discussion). Of the 43 migrant species for which we have adequate reliable arrival data, 31 did arrive earlier than the average date calculated through 2011. Both the median and the mode for the number of days early for these species was 2 days. Thirteen species arrived four or more days earlier than average. A few short-distance migrants had record-early dates for Dearborn:
  • Tree Swallow on 18 March, previous early date 22 March
  • Field Sparrow on 18 March, previous early 24 March
  • Chipping Sparrow on 26 March, previous early 30 March
Of the long-distance migrants, new records were:
  • Nashville Warbler on 16 April, previous early 20 April
  • Canada Warbler on 4 May, previous early 5 May
So, nothing particularly outstanding. Many thanks to Darrin O'Brien who assisted with surveys this spring.

Wednesday, June 20, 2012

Dickcissels in Dearborn

(Edited 25 Jun with new data)
There are at least a dozen Dickcissels (maybe more) in the wildflower fields at Ford Road and Mercury. This is the field marked "8" on our page of Ford fields. Note that the fields are marked "No trespassing," so if you visit, please scan from a roadside and be careful of traffic. I first heard these birds on 18 June. My husband Darrin O'Brien saw a bird carrying food later that day, indicating that they are probably nesting. Our survey on 24 June located at least 10 singing males and 2 females. There are also dozens of Savannah Sparrows in this field.

On 20 June, Jim Fowler and Dave Washington located two more Dickcissels in the fields on the south side of Lundy Parkway (field number "6"). Darrin had 9 there on 21 June, and we had eight on 24 June.

The two small wildflower fields ("1a" and "1b") have two birds. So, at least around two dozen Dickcissels in Dearborn!

The last Dickcissel record in Dearborn was from 1 July 1907! The only other confirmed record I could find when researching my book on Dearborn birds was a flock near the Rouge River from 30 July 1899. Three of these birds were collected, and I have examined the specimens in the University of Michigan Museum of Zoology in Ann Arbor. All of these records are attributed to "Springwells." Dearborn's present borders were established in 1929; prior to that portions were known as Fordson and/or Springwells. I believe the 1907 record was from somewhere near what is now Rotunda and Schaefer in Dearborn. The route of the Rouge River has also been altered since 1899, but I think that the 1899 specimens are also from Dearborn.

Long time, no see! The last Dickcissel record from Dearborn was in 1907.This male, 20 June 2012.
Photo by Cathy Carroll, used with permission, all rights reserved.

Female Dickcissel, Dearborn, 20 June 2012.
Photo by Cathy Carroll, used with permission, all rights reserved.

Dickcissels are specialist birds that depend on grasslands. They are known for their unpredictable, semi-nomadic movements, in particular outside of their core prairie habitat in the Great Plains. It's hard to know where they'll show up from year to year.  While they can be quite adaptable and will use non-prairie grassland habitats, the loss of native prairie has been a factor in dramatic population declines. These little birds winter far into South America, mostly in the grasslands of central Venezuela. They winter in huge flocks and can be considered pests on grain farms. They are hunted and poisoned regularly, which no doubt has contributed to declines in their numbers.

The wildflower fields the Dickcissels are using have a high diversity of herbaceous plants which are required by the birds for song perches and nesting substrate. In the great photos above, by Cathy Carroll, the birds are perched on Gray-headed Coneflowers  (Ratibida pinnata), a wonderful native wildflower. The wildflowers also provide for a wide diversity and abundance of insect prey, especially grasshoppers and butterfly and moth larvae, which are needed to raise their young.

Many of the fields planted by Ford Motor Company are sunflowers or hay fields. Those that have wildflowers are the least manipulated by mowing or disturbance and have the most interesting birds. Perhaps this will encourage Ford to convert more of the fields to wildflowers!