Sunday, October 24, 2010

Cooper's Hawk, Belle Isle

Another Sunday morning, another visit to Belle Isle.  Lately I've been pressed for time and my weekends go by in a blur.  I'd like to do some birding elsewhere, especially as Belle Isle has been hit or miss for me this fall, but with my weekend time crunch and the close reliability of Belle Isle, it's my default location just to get some birding and outdoor time in. 

The woods were generally quiet on Sunday, but then I came upon a photo jackpot perched low in bushes just along the creek on the south side of the nature trail.  I was surprised that this Coop (Accipiter cooperii) didn't fly off.  I had an opportunity to take a lot of photos, but my presence was finally too much for the bird and it flew, disappearing on the creek side of the bushes.  Moments later it came out of the bushes and flew directly at me down the center of the path before lifting and disappearing into the trees.

On the west side of the athletic fields there were six Field Sparrows (Spizella pusilla). 

The large numbers of White-throated Sparrows (Zonotrichia albicollis) of the prior weekend were greatly diminished.  I did not see White-crowned Sparrows (Zonotrichia leucophrys)  until I birded around the Anna Scripps Whitcomb Conservatory, an area of the park I rarely visit. 

Finally, on the grassy area west of the conservatory building, this tattered Common Buckeye (Junonia coenia) was flying around trying to nector on dandelions.  One of my favorite butterflies, I had opportunities this past August to photograph beautifully fresh buckeyes (second to last photo).  Seeing this worn butterfly stirred some sad feelings.  I checked with Roger Kuhlman.  Buckeyes are seen in Michigan into November and often at warmer places like Belle Isle.

There have been days of great diversity of birds at Belle Isle reported by others, especially earlier in September, all days that were missed by me. The Friends of Belle Isle group have been around the nature trail to clear large areas of invasive honeysuckle that has left these areas barren of plants and berries.  In areas where I usually find good birds there is no where for them to hide and forage.  I'm wondering how this may impact future fall migrations of thrushes and other berry eaters. Certainly, for me, the numbers of these species have been much fewer than prior fall visits.  Julie Craves has written about how non-native berry species may be critical to weight gain amongst birds in fall migration and she is currently studying this issue.


Recently Julie wrote more specifically about buckthorn and posted this to the Michigan birders listserve.  A little long for this blog, but well worth reading.

Many birds eat buckthorn, both Common Buckthorn (Rhamnus cathartica) and Glossy Buckthorn (Frangula alnus).  For the past several years, the fruit preferences of birds in the fall has been the focus of my research.

Neither of these species are native to North America, they are both invasive and both have various ecological liabilities.  However, they also perform an important ecological function as food for migratory birds, especially in urban areas where native fruits may be scarce.  My research has indicated that a number of bird species eat buckthorn even when native species are available.  Birds are able to gain mass when these species are part of their diet.

Our perceptions of non-native fruits as being "bad" are not entirely accurate.  We are learning that the nutritional needs of migratory birds are much more complex than previously believed, and the nutrient and chemical content of these fruits may be much more appropriate than we thought.  Also, the buckthorns have been in North America for over 200 years and the fruit characteristics may be evolving to suit our migrant birds; similar evolutionary adaptations to migrant birds have been documented elsewhere.

Whether or not the ecological benefits of these species outweigh their liabilities remains to be discovered.  Rouge River Bird Observatory (RRBO) has started an integrated approach to this question.  My research program is gathering data on what birds are eating, we are putting together a team of undergraduate students who will be helping with determining the physical and chemical composition of a wide array of fruits available to birds in the fall, and I'm supervising a student and a volunteer who are making field observations of bird foraging behavior.

The fact is that birds are more frequently encountering disturbed and urban areas during migration, and these non-native plant species are well-established.  Eradication is extremely labor intensive and usually not completely successful.  We need to understand how birds and other wildlife use these non-native species and how (or if) they should be managed.

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