Cloacal Sperm in Spring Migrants: Occurrence and Interpretation

Abstract

Cloacal sperm were studied microscopically in cloacal lavages from 448 birds representing 70 migratory species, from Galveston, Texas, and Foley, Missouri. Representatives of 20 of these species sampled in the spring had cloacal sperm; at least 38 of the 39 individuals with sperm were males. A conservative interpretation of cloacal sperm in male migrants is that they represent spontaneous discharge from the ductus deferens or its glomus seminale, specifically in individuals that are ready for breeding. Although most of the migrants with cloacal sperm were not far from the known nesting range of the species, others were 30 to 900 km south of the southern limits of the known breeding range (Nashville Warbler [Vermivora ruficapilla], Rose-breasted Grosbeak [Pheucticus ludovicianus] and Painted Bunting [Passerina ciris]). There appear to be functionally significant differences among species of passerine birds in the timing of sperm emission and the physiological readiness for breeding; these processes apparently start in some species during spring migration. This study is based chiefly upon my systematic collection and analysis of cloacal lavages (washes) from feral birds. The initial purpose of the lavage technique and its application during banding and field studies was to ascertain the feasibility of developing rapid, noninvasive, and repeatable methods for identifying the sex and physiological state of individual birds in the course of field studies and under natural conditions. My first notable finding from the use of this technique was that spermatozoa (sperm) can be found in the cloaca of reproductively active individuals of either sex and particularly in a number of passerines (Quay 1984a, b). This led to the present study, which had the goals of: (1) determining the occurrence ofcloacal sperm in male spring migrants, (2) comparing species in these occurrences, (3) comparing results from two localities (Galveston, Texas, and Foley, Missouri) representing two latitudes in the central zone through the United States, and (4) making a start in determining the biological meaning of sperm in the cloacas of male migrants. A general review of some of this work has appeared in an abstract (Quay 1984b). STUDY AREAS AND METHODS I captured birds by mist nets, banded them and gave them cloacal lavages. During 1982, netting was done in the back and side yards of my residence at the NE end of the town of Galveston, Galveston County, Texas. Nets were in operation 6 and 14-31 March, 1-4, 14-21, and 25-30 April, and 1-13, 22, 26, 30 and 31 May, generally from before dawn to after sunset, and with breaks in the morning and afternoon. During 1983, the study area was a farm with mixed habitats on the bluffs on the W side of the Mississippi River, 5 km (airline) NNW of the town of Foley, Lincoln County, Missouri. Here, up to 16 nets were op ra ed continuously from early in the day 30 April through early in the day 7 May 1983 (total = 98 net-days). Nets were inspected at approximately hourly intervals during the day and less frequently at night. At both localities, I personally captured and processed all birds. After capture, birds were placed in individual light-weight, brown paper bags until processed about 5-20 min later. The procedural steps are noted here for two reasons: (1) they provide the basis for determinations of sex, age-class, and possible correlates of occurrences of cloacal sperm, and (2) they may possibly be related to presence or absence of cloacal sperm in some individuals or species through physical handling. Therefore, to facilitate the obtaining and interpreting of results of subsequent studies, all of the methods that I used are noted. These were: (1) weighing with a Mettler Type P-120 top-loading balance to the nearest 0.1 g; (2) measurement of wing chord and tail lengths; (3) determination of sex and age-class insofar as possible; (4) recording, where relevant, external characteristics such as the relative development of the cloacal protuberance of males, the size and degree of edema of the incubation/ br od patch, and skull pneumatization; (5) banding; and (6) the taking of cloacal lavages. Procedures (2) through (5) above followed those of the North American Bird Banding Manual vol. II (Bird Banding Techniques) (Bird Bandi g Offices of the United States and Canada 1977). Determination of sex and age-class