The damaging effect of Great Blue Heron (Ardea herodias) excrement on nest trees was determined by observation and Hellige-Truog soil analysis methods. In large heronries high chemical concentrations kill nest trees and result in movement of heronry boundaries to o live tree area

Howe, John F.

Kerns, James M.

English

University of Minnesota, Morris (UMM): Digital Well

Journal of the Minnesota Academy of Science Volume 34 Number 2 Article 7 1967 Factors Determining Great Blue Heron Rookery Movement James M. Kerns St. Olaf College John F. Howe St. Olaf College Follow this and additional works at: https://digitalcommons.morris.umn.edu/jmas  Part of the Ornithology Commons Recommended Citation Kerns, J. M., & Howe, J. F. (1967). Factors Determining Great Blue Heron Rookery Movement. Journal of the Minnesota Academy of Science, Vol. 34 No.2, 80-83. Retrieved from https://digitalcommons.morris.umn.edu/jmas/vol34/iss2/7 This Article is brought to you for free and open access by the Journals at University of Minnesota Morris Digital Well. It has been accepted for inclusion in Journal of the Minnesota Academy of Science by an authorized editor of University of Minnesota Morris Digital Well. For more information, please contact skulann@morris.umn.edu. A Practical Approach to Evaluation of the Germicidal Efficiency of a General Purpose Military Disinfectant. Applied Microbiology, 9:497-501. VESLEY, D. and MICHAELSEN, G. S. 1964. Application of a Surface Sampling Technic to the Evaluation of Bacteriological Effectiveness of Certain Hospital Housekeeping Procedures. Health Laboratory Science, 1: 107-113. VESLEY, D., KEENAN, K. M. and HALBERT, M. M. 1966. Some Aspects of Time and Temperature Selection for the Incubation of Rodac Surface Samples. Applied Microbiology, 14: 203-205. WALTER, C. W. and KuNDSIN, R. B. 1960. The Floor as a Reservoir of Hospital Infections. Surgery, Gynecolo-gy & Obstetrics, 111: 412-422. WEBER, G. R. and BLACK, L.A. 1948. Relative Efficien-cy of Quaternary Inhibitors. Soap and Sanitary Chemi-cals, 24(10): 134-137, 151-155. Factors Determining Great Blue Heron Rookery Movement* JAMES M. KERNS 1 and JoHN F. HowE 2 St. Olaf College, Northfield ABSTRACT - The damaging effect of Great Blue Heron (Ardeo herodias) excrement on nest trees was determined by observation and Hellige-Truog soil analysis methods. In large heronries high chemical concentrations kill nest trees and result in movement of heronry boundaries to o live tree area. The literature indicates that the effect of excrement on soil composition leads to consequent death of nesting trees in mature colonies of Great Blue Herons (A. hero-dias). Roberts (1932 and 1938) reported a heronry in Minnesota of several hundred nests in elm and basswood trees which had died as a result of their being occupied by the birds. He concludes that this condition is only ex-istent in large heronries. Bent ( 1963) cites a similar ex-ample in a Maine heronry where many of the nests were in dead trees. Young ( 1936) found that the roosting ac-tivities of a large flock of starlings (Sturnus vulgaris) re-sulted in damaged White Pine (Pinus strobus); high soil concentrations of N03 , P, and K resulted from accumu-lated bird droppings. Young herons deposit the viscid effluent in the coarse nest where they stand so that the droppings fall through on to the branches below giving a whitewashed appear-ance to the trees. It is uncertain whether the death of the trees is caused by direct contact of the excrement on the branches or by the action of leached chemical compo-nents on the roots; both explanations seem likely. The present authors investigated the effect of excrement on nest trees by analysis of soil composition. These results combined with environmental factors were related to ,:, Studies were supported by the National Science Foundation through the Associated Colleges of the Midwest Field Station, Basswood Lake. Acknowledgment is due Evan Hazzard, Biology Department, Bemidji State College and Howard Orr, Biology Department, St. Olaf College for valuable criticisms on the manuscript and David Lyon, Biology Department, Cornell College, Mount Ver-non, Iowa for his encouragement and advice in this project. 'B.A. 1966, Biology, St. Olaf College; currently working for a graduate degree in Veterinary Anatomy at Purdue University, West Lafayette, Ind. and employed as a Graduate Instructor. "B.A. 1967, Lawrence University. 80 present tree conditions and the corresponding movement of nest sites to the live tree or future location (Fig. 1). The study area was the Basswood Lake heronry near Ely, in existence since 1920 ( correspondence with R. Halliday). The first causes of movement were probably not directly related to the effects of excrement, but to unnatural conditions. Because the nesting trees in the early location were cut down, the herony supposedly moved westward in about 1947. A fire, reported in 1961, burned many of the trees in the same area. In its present location the rookery area nests are located only in the tops of live and dead Red Pine ( Pin us resinosa). The dead pines are beyond the range of the fire and the live pines extend SW on a high ridge, an area to which the gradual movement of active nesting sites is taking place. Pictures taken by C. Ahlgren, of the Quetico-Superior Wilderness Research Center, over a 10-year time span give evidence of westward movement. Our research in-volved collecting quantitative data rel'ating to causes of this movement. Methods The studies were conducted on an island 4.5 miles NE of the ACM Field Station in Meriam Bay, Basswood Lake, Ontario during June and July, 1965. The proposed 5-year study began in 1964 and included rookery map-ping into 50-foot square grids, a young bird population count, and general observations (R. Grooters and D. Werner). In the present study standardized soil collection pro-cedures were used to sample the old, present, and future rookery areas. Five random locations in each area were permanently marked, then surface litter was cleared away. Separate samples were taken from one, two, and The Minnesota Academy of Science N r MERIAM BAY FUTURE PRESENT BASSWOOD LAKE SCALE: I inch: 130 feet of 1961 fire [J herbaceous growth htl dead red pine C live red pine FIGURE 1. Map of heron rookery areas. eight inch levels (humus, trans1t10n, and mineral layers respectively); they were dried and run through a stand-ard sieve series. Chemical analysis was by the Hellige-Truog methods for acidity, P, K, NO:i, Ca, NH:i, and Mg with the available concentration expressed in lbs per acre for each soil level. These quantitative elemental units were converted to relative values for ease in graphic representation. To evaluate the effect of the differences in soil compo-sition it was necessary to record 1965 nest tree condi-tions, fallen nests, and new nests since 1964. The bound-ary of nest trees active in 1964 was compared to that in 1965 to determine the westward movement. Results Concentration values of the separate soil levels were reduced to an average value. The concentration of P and K increased from the surface level to the mineral level while NO:i, Ca, and acidity were highest at the surface. The values of Mg and NH:1 showed no variance in the three rookery areas, so they were disregarded. The present rookery area in its most active locations was more acidic and more concentrated in P, K, and NO:, than the vacant future rookery area, a comparison standard. The values in the old rookery were interme-diate, which probably resulted from the effects of weath-ering after it had been abandoned. Our data indicate a deficiency of Ca in the old and present rookery areas (Fig. 2). Journal of, Volume Thirty-four, No. 2, 1967 Observation of nest trees in the live-dead tree border indicated many nest trees reported to be alive in 1964 were dying in 1965. 95 % of the nests were in 45 dead and 41 live pines. From fallen nest remains and previ-ous nest data, it was determined that 26 nests had fallen in one year; there was evidence of 18 newly built nests during this period, or a net loss of 8 nests. These com-bined data of active nest site boundaries suggest a move-ment rate of about 25 feet per year westward (Fig. 3). Discussion Our data support the general hypotheses that heron excrement has a damaging effect on nest trees in large heronries and that when possible directional movement of nest sites results. Until improved techniques are developed and more quantitative data is accumulated, it is impossible to state with certainty the relative importance of leaching in each soil level and the specific element causing the damage. In-terpretation of the results is hypothetical because of com-plexities in diagnosis. McMurrtrey (1949) suggests that unbalanced nutritional requirements may result from a deficiency or an excess of an element in relation to the others. The symptoms produced may be due to the high con-centration of P, K, or NO:1 interfering with the solubility, absorption, or utilization of another element. It is sug-gested that the high acidity has a toxic effect and that di-rect contact of the excrement on the branches reduces 81 CONC. PHOSPHORUS POTASSIUM NITRATE CALCIUM ACIDITY pH 2 x HI I 4.0 HI MED s.o 6.0 TRACE A B C A B C A B C A B C A B C A- OLD ROOKERY B- PRESENT C- FUTURE FIGURE 2. Soil analysis of rookery. the photosynthetic area of the trees. Partial defoliation was caused mechanically by the adult herons landing at the nest. When weakened, the trees no longer seem able to sup-port the bulk of the nests which are soon blown down by strong winds. This explains the net loss of nests since 1964 and the accompanying movement. It is unlikely that these factors affect the total heron population, but Wallace ( 1963) suggests that the proximity of colony neighbors stimulates breeding and peripheral nesters are often unsuccessful. More information is needed to relate these reports. Correlating the previous history of the Basswood her-onry with evidence from this study seems to show an ov-erall movement of 20-30 feet per year, but no single fac-tor can explain the reason since many environmental in-terrelationships seem to be involved. References AHLGREN, C. (in Groote rs). BENT, A. 1963. Life Histories of North American Marsh 82 Birds. New York, Dover Publications, Inc., pp. 101-114. GROOTERS, R. and WERNER, D. 1964. Great Blue Her-on Studies. unpublished. HALLIDAY, R. (in Grooters). McMURRTREY, J.E. JR. 1949. Plant-Nutrient Deficiency in Tobacco. In Baer, Firman E., et. al. Hunger Signs in Crops. Washington, The American Society of Agronomy, p. 20. ROBERTS, T. 1932. The Birds of Minnesota. University of Minnesota Press, pp. 175-179. ROBERTS, T. 1938. Log Book of Minnesota Bird Life 1917-1937. University of Minnesota Press, p. 49, 127. WALLACE, G. 1963. An Introduction to Ornithology. New York, The MacMillan Co., p. 130. YouNG, V. 1936. Edaphic and Vegetational Changes Associated With Injury of a White Pine Plantation by Roosting Birds. J. For., 34: 512-523. The Minnesota Academy of Science ________ .., 1964 ROOKERY BOUNDARY ------1965 ROOKERY BOUNDARY active center ! SCALE: I inch: 40 feet ---------FIGURE 3. Grid map of rookery boundary movement. Journal of, Volume Thirty-four, No. 2, 1967 N t 83 

Factors Determining Great Blue Heron Rookery Movement

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Factors Determining Great Blue Heron Rookery Movement

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