Reproductive Cycle of the Mallard Duck

Considerable work has been done on the behavioral patterns associated with the reproductive cycle of waterfowl. The books by Sowls (1955) and Hochbaum (1959), and the papers by Ramsey (1956) and Johnsgard (1960) are notable in this regard.There has been, however, very little research on the gonadal changes associated with the cycle.With this in mind, a study was undertaken in southeastern Washington the main objective of which was to trace the cyclic changes of the reproductive organs of the Mallard (Anas platyrbynchos). METHODSWild Mallards (81 males and 57 females) were collected from March, 1958, through June, 1959.Five additional males were taken in May of 1960.An effort was made to record the undisturbed behavioral actions of each specimen immediately prior to collection.Such notes helped greatly in later categorization.The desired tissues were excised in the field and fixed in AFA solution (glacial acetic acid, 10 parts; 37 per cent formalin, 10 parts; 95 per cent alcohol, 30 parts; and distilled water, 50 parts).All collected materials were brought back to the laboratory for examination and the recording of various data.The laboratory procedures were as follows:Males.-Testicular length and width (measured in the dorso-ventral plane) in millimeters were obtained with a vernier caliper.The testes used for microscopic analyses were dehydrated in dioxane and embedded in paraffin.The preparations were stained with Heidenhain' s hematoxylin and counterstained lightly in eosin.The penis was removed by cutting along its lines of attachment flush with the cloaca1 wall.This procedure was simplified by pressure eversion of the penis through the cloaca1 opening at the time of collection.After removal the penis was weighed.It was found that penis weight was a much better relative measurement than length.' Females.-Thelargest follicle on each ovary was measured in millimeters using the vernier caliper.Measurements were made in the same plane as the stigma.Oviduct length (to the nearest five millimeters) was measured by cutting the supporting ligaments (which tend to keep the structure in a convoluted position), and then gently straightening the tube along a millimeter rule.Both sexes.-Bursaewere dissected away from the cloacae, and their maximum outside length measured with a millimeter rule.Diameter measurements were made with a vernier caliper near the middle of each bursa.All excised structures, after having been carefully dissected away from extraneous tissues, were weighed to .OOl gm. on a chain balance.Weighings were made in a sealed jar containing a piece of filter paper saturated with alcohol.This method minimized the degree of error from evaporation.The weight of the jar was standardized after every other weighing to maintain a high degree of accuracy.The feather development of each specimen was closely inspected.Plumage data were valuable in categorizing birds during later analyses. BURSA OF FABRICIUSIn juvenal Mallards, the bursa is a conspicuous, glandular organ with a well developed lumen.On the basis of bursae which were examined from flightless young, it appears that the size of the structure in Mallards is maximum at about the time flight is achieved.The mean bursal measurements for nine juveniles (males and females capable of flight) taken during July and August are as follows: length, 32.1 mm.; diameter, 8.0 mm.; and weight, 1.54 gm.