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Illinois Birds, Wood Warblers

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Illinois Birds, Wood Warblers ILLINOIS BIRDS'. Wood Warblers Jean W. Graber, Richard R. Graber, Ethelyn L. Kirk HRT.v** Biological Notes No. 1 m «>* -x^r m*4, S* He,;v /- & b*r € 2tB Illinois Natural History Survey State of Illinois Department of Energy and Natural Resources (Campaign, Illinois-April - 1983 Natural History Survey Division . ILLINOIS BIRDS: Wood Warblers Jean W. Grabe-, iMchard R. Craber, and Ethelyn L. Kirk Illinois ornithology reached an important bench mark forest habitat. Twomey (1945) and Calef (1953a, 19536) with the publication of Bohlen's (1978) distributional studied populations in east-central Illinois forests, but their checklist. This reference provided for the first time a com- data on migrant populations were not separated by species. plete, or virtually complete, list of Illinois birds. It is a 3ecause of our interest in the problems faced by migrant valuable foundation for the work that still needs to be done. populations during their sojourn in Illinois, in 1979 we in- This paper, the ninth in a series on Illinois bird popu- flated concurrent studies on ( 1 ) the numbers of transients in lations, deals with the wood warblers (Emberizidae, four arboreal habitats and (2) the availability of food Parulinae). The order of the species in this account follows resources in these habitats. To gain understanding of the the 1957 American Ornithologists' Union Check-list, 5th ed., problems of migrants in different situations, we chose to and not the 34th supplement, which was published while this study two very different areas: (1) the heavily forested paper was in press. Of the 43 species of warblers that have southern tip of Illinois, where habitat availability for ar- been reported (4 questionably) in Illinois or its border areas, boreal species appears to be reasonably ample and (2) the 23 have been known to breed (19 regularly) in the state. Most very lightly forested prairie peninsula of east-central Illinois, of those that breed— along with 16 species that occur only as where arboreal species might be pressed to find sufficient migrants — are also represented by sizeable transient popula- resources. The data on food resources are being published tions in spring and/or fall (Table 1). elsewhere. The bird population data are included in this In a previous paper (Graber et al. 1979) we introduced paper. the subject of "dilution" — the possible influence of habitat To census the bird population, we used the method used availability on migrant population density. While breeding by Gross — counting all birds within a transect 27.4 m (30 populations distribute themselves more or less uniformly in yards) wide on a route 6-8 km long through the habitat the available habitat, migrant populations arrive in large (Graber & Graber 1963). Routes through each habitat were numbers at a given area and must survive (or not) on the marked in advance of the censuses and were followed resources they find there. The problem is undoubtedly of throughout the seasons. The specific study areas in east- great significance to the warblers. They are mainly night central Illinois were (1) mature upland oak-hickory forest. migrants and are virtually all arboreal species (Table 1). The (2) upland forest edge and shrub, and (3) mature bot- habitats which a flight of warblers reach after a night migra- tomland elm-maple-hackberry forest, all at Allerton Park, tion may be unknown to the birds except in the perspective Piatt County. Study areas in the south were (1) mature that evolutionary history provides, and evolution cannot upland oak-hickory forest, (2) upland forest edge and shrub. prepare a wild population for the elimination of habitats at (3) pine forest, all in the Warbluff area north of Golconda in the rates perpetrated by modern man. Because of this Pope County, and (4) mature bottomland oak-maple-gum change it is increasingly important to know at least (1) what forest at Heron Pond Nature Preserve, Johnson Countv. the populations are both qualitatively and quantitatively, (2) Because central Illinois bottomlands were flooded during which habitats the populations are using, (3) what resources much of the 1981 migration seasons, densities for that in the habitats are being used, and (4) the availability of habitat include only the 1979-1980 data. those resources. The general policies followed in this paper are the same Although some breeding and winter populations of birds as in previous papers in the series. Certain matters discussed have been measured in some Illinois habitats (Kendeigh in many of the species accounts can be explained here for all 1944, Graber & Graber 1963, and others), the only attempts With the exception of data from the Christmas bird counts, known to us to measure migrant populations in specific the counts of birds referred to are counts by single observers, habitats were the studies of Forbes (1907), Forbes & Gross or in the case of the transect censuses, two observers together. (1923), Twomey (1945), and Calef (1953a, 19536). Most of Counts by multiple observers are not comparable. the data on migrant populations collected by A.O. Gross and In referring to museum specimens, we have used ab- S. A. Forbes at the Illinois Natural History Survey were never breviations: FMNH for the Field Museum of Natural History published, but Gross' field notes are still in existence, and we at Chicago, EIUC for Eastern Illinois University Collections. have incorporated his warbler data for 1906-1909 in this INHS for the Illinois Natural History Survey, ISM for the Il- paper. Gross worked mainly on cultivated habitats, and the linois State Museum at Springfield, ISUC for the Illinois data are very valuable, but he gathered little information on State University Collections at Normal, NIUC for the North- ern Illinois University Collections at De Kalb. SIUC for the Southern Illinois University Collections at Carbondale. UIM 1 iv I 1 pa pel is published bv aulhurilY of the Slate of Illinois and is a contribution from the Set for the University of Illinois Museum at Urbana, I'MMZ for nun of Wildlife Research of the Illinois Natural History Suiscs l)i Jean W. Crabei and f>i Richatd R. Grabei .ire Wildlife Specialists, and the late Miss Ethelyn I. kirk served is .1 the University of Michigan Museum of Zoology at Ann Ar- Technical Assistant in the Section of Wildlife Research. bor, and USNM for the U.S. National Museum in hi ,1, I nun, outside referees recommend each manuscript submitted lor publication in the Biological Notes series before it is .u<cpted Washington. D.C. V April 1983 Graber. Graber. & Kirk: Illinois Birds: Wood Warblers We have also often used abbreviations for the regions referred to in the tables, i.e.. N for North, C for central, and S for south. The regions are shown in Fig. 50. For noteworthy records (dates, numbers of birds, dc.) we have provided the source reference — the name of the observer, if unpublished. Where no reference is cited, the record is our own. Though we have used metric measurements or conver- sions for our own data, we have not converted measurements from the literature or from other observers to metric, nor have we attempted to assign technical names to vernacular names given in the literature though we have used technical names for our own records. In the species accounts we have often referred to William Dreuth's data on the migration at Chicago, published by Clark & Nice (1950). To save space, we have often omitted the complete citation by simplv referring to Dreuth. We have also frequentlv compared our counts of birds in east-central Illinois with those of Professor Frank Smith and his students, Fig. 1. — Numbers of warblers killed al television towers in central who made counts in the vicinity of Urbana between 1903 and Illinois during the fall migration season. 1957-1979. The solid line represents the largest number of warblers found at single tower at 1925. The years shown on some of the migration graphs were anv any date. The dash line shows numbers found at several towers on one the years of their highest counts. Smith published (1930) date. some of those data, but we have extracted counts of in- dividual observers from the original field notes now in our few birds were found at towers in spring. Tower areas were possession. The principal observers were Frank C. Gates not routinely searched, and coverage was very uneven from (1908-1910). Alfred O. Gross (1904-1906). Thomas E. year to year and month to month. Musselman (1908-1910), and Smith himself (1903-1925). In the tabulations of population densities (e.g., Table 1) These data are often cited in the accounts as "Smith et al. at the season for each individual species extended from the date Urbana." we first encountered that species to the date (inclusive) we In discussing ratios between numbers of birds seen in last encountered that species, whether it was within or out- spring and fall, we have often presented both the ratio from side the census transect. Because migrants tend to come in our regional field counts (1967- 1970) and the ratio observed "waves" (many on 1 day and on another, none at all), we in our census transects (1979- 1981 ). Ratios from the two sets have omitted the minimum counts, which are often zero. of data usually show the same trend, but sometimes differ in The mean density is the mean for all (including negative) actual numbers by a sizeable margin. Annual variation is censuses in the season as defined for each species. The data one possible explanation of the differences. The censuses are on range of densities refer to census areas of at least 16 ha.
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