Studies of Birds Killed in Nocturnal Migration

Volume 10, No. 1, Pp. 1-44, 6 Figures in Text, 2 Tables

Published September 12, 1956

UNIVERSITY OF KANSAS Lawrence, Kansas

PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1956

26-3856

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Studies of Birds Killed in Nocturnal Migration

BY HARRISON B. TORDOFF AND ROBERT M. MENGEL

Contents

PAGE

Introduction 4

Accidents to Migrating Birds in early October, 1954 6 General 6 Accidents at Topeka, Kansas 6 Description of WIBW-TV tower 7 Weather conditions 7

Acknowledgments 7

Notes on the Species Killed at Topeka 8

Randomness of the Sample 17

Number of Migrants 18

Differential Migration of Sex- and Age-classes 20 History of the subject 20 Differential migration of sex- and age-classes as shown by the Topeka sample 23

Molt in Relation to Migration 29 General comment 29 Molt in the Topeka sample 30

Size Differences according to Sex and Age 31 Linear measurements 31 Weights 32

Computations of Longevity and Survival 38

Processing of Samples 38

Summary 39

Literature Cited 41

Introduction

This paper is primarily an analysis of a sample of migrant birds killed in the autumn of 1954 by striking a television tower one mile west of Topeka, Shawnee County, Kansas. Secondarily, some aspects of migration involved in studies of this kind are discussed and historical background is presented.

Considerable interest has been occasioned in recent years in the eastern United States by large-scale accidents to night-migrating birds. Most accidents have occurred in the autumn. The widespread adoption by airports of an instrument called the ceilometer, which measures the height of cloud ceilings by reflecting from them a high-powered beam of light, has proved under certain conditions to be catastrophic to night-flying birds. Among the recent reports of such accidents are those of Spofford (1949) and Laskey (1951) for Nashville, Tennessee, Howell and Tanner (1951) for Knoxville, Tennessee, and Lovell (1952) for Louisville, Kentucky. Recently Howell, Laskey, and Tanner (1954) reviewed ceilometer "tragedies" without being able to determine the exact reason for their lethal effectiveness. Less publicized so far have been mass collisions of birds with another class of obstacles, tall radio and television towers. These slender towers, usually 500 to 1000 feet tall, are increasing rapidly in numbers and there is reason to suppose that they will take a correspondingly larger toll of bird life.

Notice has long been given by ornithologists to mass destruction of birds by more conventional solid obstructions to passage, and newspapers occasionally mention birds killed at such well-known points as the Washington Monument and the Empire State Building.

Seventy-five years ago, J. A. Allen (1880) published the results of questionnaires circulated by William Brewster to lighthouse keepers. Brewster himself (1886) described destruction of birds at a lighthouse in the Bay of Fundy, paying keen attention to behavior of the birds and the exact conditions under which nocturnal flight and accidents occurred. The subject also received attention in several countries across the Atlantic. Destruction of birds at Irish lighthouses was carefully noted over a period of years and the results were published periodically, culminating in R. M. Barrington's massive report (1900) which remains in some ways the most thorough of its type.

While conservation-minded individuals have been concerned with the tremendous mortality involved in these various events, the ill wind blows some good in that, properly used, the data provided by such accidents can shed light on many obscure aspects of bird migration. Each accidental kill of birds affords a cross-section, approaching in variable degree a random sample, of the migrants passing a given point on a given date. The types of information provided by such kills are numerous, for example: (1) information on the presence of various species and the dates of their occurrence; (2) information on the relative abundance of species; (3) quantitative data on the relative sizes of males and females, and immatures and adults (of importance to taxonomic ornithology); (4) information on the relative times of migration of males, females, adults, and young; (5) information on molts and plumages; (6) quantitative information on composition by subspecies of migrants of the same species; (7) physiological data (fat condition, etc.) pertinent to the study of migration; and probably others.

In spite of the great potential of this kind of material, the majority of ornithologists with access to such data have contented themselves with listing the species and sometimes the numbers of birds killed. A few have gone further. James T. Tanner (unpublished) attempted to compute the longevity of the Ovenbird (Seiurus aurocapillus) by analysis of ceilometer-killed birds at Knoxville, Tennessee (see below). Mention should be made of the reports of Rintoul and Baxter (1914) supplemented by Ticehurst (1916) who used rather small numbers of birds killed at Scottish lighthouses in studies of molt. However, the only effort to utilize the results of accidental kills on a large scale over a period of years appears to have been that, already mentioned, of Barrington (1900) and his co-workers in Ireland. An idea of the potentialities of the large recent kills in the United States may be obtained when it is recalled that in the 18 years of Barrington's work, which embodied some 1000 reports from lighthouse keepers, Barrington obtained for study only about 2000 specimens, many of these consisting of wings and feet only (Barrington's paper not seen in original; see J. A. Allen, 1901:205). More recently Dobben and Bruyns (1939) have analyzed the age and sex classes of some birds killed at lighthouses in Holland.

As far as we have learned, there is no previous thorough analysis in the literature of large, accidentally-killed samples of birds. On the following pages we emphasize some of the uses which can be made of such material. We think that intensive analyses of such events, whenever they occur, should become a regular part of ornithological investigation and that integration of numerous studies of such incidents will provide an unprecedented mass of information on migration.

Accidents to Migrating Birds in early October, 1954

GENERAL.--The few days around the end of the first week of October, 1954, were notable for a series of accidents which occurred to migrating birds over much of eastern United States. So far as we know, these were all associated with an extensive belt of bad weather (cold fronts and stationary fronts) which covered much of the country during that period, and the accidents involved ceilometers and solid structures alike. Accidents known to us occurred as far south as Macon, Georgia (David W. Johnston, letter: Nov. 1, 1954), as far north as New York City, where many migrants were killed at the Empire State Building (New York Times, Thursday, October 7, 1954, p. 1) and elsewhere, and as far west as Smoky Hill Air Force Base at Salina, Kansas (ceilometer, October 7, some birds received at the University of Kansas). Some of the above, and incidents from a number of other localities, were mentioned in varying detail in Audubon Field Notes (vol. 9, no. 1, pp. 6, 10, 15, 17, 18, 32, February, 1955). Still other accidents occurred at Columbia, Missouri (Richard P. Grossenheider, verbal communication), and Topeka, Kansas (present paper). Some probably have escaped our notice; summaries of some of these will probably appear in ornithological journals for some time to come. At Robins Air Force Base near Macon, Georgia, at least 50,000 birds were killed, of which about 2500, representing 54 species, were picked up (Johnston, loc. cit.).

ACCIDENTS AT TOPEKA, KANSAS.--At Topeka, Shawnee County, Kansas, all birds were killed by collision with the newly-erected (1954) television transmitting tower of station WIBW-TV. This tower is one mile west of the city.

The first casualties (see Table 1 for all others) were a Sora (Porzana carolina) and a Yellow-bellied Flycatcher (Empidonax flaviventris) found on September 7. The major accidents, however, occurred on the nights of September 24-25, September 30-October 1, October 5-6, and October 6-7. Totals of birds picked up (probably over 95 per cent of birds killed) are given in Table 1, in which each date given is that of the day after the kill, i. e., the date on which the birds were collected.

All major kills occurred on cloudy and foggy nights associated with frontal weather. Throughout the period a few birds struck the tower even on fairly clear nights, and minor but appreciable "falls" occurred on the nights of October 4-5, 7-8, and 22-23. A few birds killed probably were overlooked for a time and found their way into later samples. This is especially probable in the case of some birds entered under date of October 23, as many of these were somewhat desiccated. Weights clearly altered by desiccation or mutilation were not recorded. Reports of these accidents have been published by Carson (1954 a, b, and c).

According to Carson (1954c:27), the majority of birds killed on nights of heavy flight fell "between three and four o'clock in the morning when skies were overcast and a cool front moved in from the north. Due to the cooperation of the watchmen it is thought that most of the birds that were killed were recovered. Of course some injured birds in hiding were not found and some were lost to predators."

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