Update: This paper has been published! It's open access so you can read online or download the PDF; click on title below - 
Craves, J.A., and N.M. Anich. 2023. Status and distribution of an introduced population of European Goldfinches (Carduelis carduelis) in the western Great Lakes region of North America. Neobiota 81:129-155. doi: 10.3897/neobiota.81.97736
 --- 
European
 Goldfinches have now been nesting in northern Illinois and southern 
Wisconsin for over 15 years. With the completion of the latest Wisconsin Breeding Bird Atlas, it's time to summarize the distribution and breeding information on this species.  
As of December 2021,
 I am working on a paper that will briefly cover the history of this 
species in North America with more detail of the status over the past 20
 years; where this species is currently found and where it has nested 
recently; a focus on the origins, spread, and distribution in the Great 
Lakes states; breeding phenology and ecology in this region; and as much
 as can be gleaned about the ecology and potential impacts of the 
establishment of European Goldfinches in North America. 
Nick
 Anich, coordinator of the Wisconsin Breeding Bird Atlas, and I are 
collaborating on this part of the project. We've met with several other 
researchers who are interested in looking at population genetics and 
morphology of European Goldfinches across the continent.
Around 2001-2004, a number of other European bird species were reported from the western Great Lakes area (scroll down on this page for details). Of those, Great Tit (Parus major)
 is still nesting in Wisconsin. I believe a couple of other species may 
still be present and reproducing, but they are much more difficult to 
quickly identify and a status update on them will have to be a future 
project, although I still collect records.
The
 initial task with the goldfinch project is just to attempt to compile a
 database of sightings for the past 20 years or so and cull important 
information from this. This data is coming from multiple sources, 
including hundreds of sightings provided directly to me from people 
responding to posts on these pages and the former Rouge River Bird 
Observatory web site. I'm indebted to these people, because they provide
 the backbone of early sightings that were never reported elsewhere. 
The majority of more recent records come from eBird, but because European Goldfinches are non-native and therefore not "countable"
 on birders' lists, they have not been adequately reported. This has 
been further compounded by differential treatment of non-native species 
in each state. We are working with all reports that have been 
submitted to eBird (including those not showing in the public maps and 
output), but believe there is a substantial amount of data that, 
unfortunately, is lost to history. The eBird data we do have is 
challenging to work with -- for example, of the 6300+ eBird records we 
have, many are duplicates of the same bird, sometimes the same day or 
multiple days at one location (which may be recorded in different ways 
by different observers).
I am no longer actively collecting data. However,
 if you have any sightings in North America from 1999-2021 that have not
 been entered into eBird, please do so. Even if they do not appear in 
the public output, we will see them when we access the eBird database, 
or they will be available to future researchers. If you have further 
questions or information, or information on other European bird species 
(list below) you can contact me via the form near the bottom of the right sidebar --> 
You can read a great deal of background on the European Birds in the Midwest page. I've included this post at the beginning of that page as many people land there first, so scroll down a bit for the earlier information.
Other posts on Net Results about European Goldfinches:
European Goldfinch: Established in the U.S.? -- Jan 2009 
European Goldfinch update -- nesting in Illinois, Jun 2009
More European Goldfinches -- nesting in Wisconsin, Jul 2009
Update on European Goldfinches -- Apr 2012