252 BULLETIN 195, UNITED STATES NATIONAL MUSEUM 



ner lining. This "door-step" or sill is always present In the female nest but is 

 lacking in the nests of the male. It is possible, therefore, to determine the sex 

 which built a given nest by checking for the presence of this sill. This projection 

 forms the floor of the opening and extends farther into the nest than any other 

 part of the lining. * * * 



One wonders what the function of this door-step might be. Perhaps it serves 

 as a protection to the eggs and young as the nest, owing to the uneven growth 

 of the supporting plants, often assumes a distorted position which would allow 

 the contents to roll out were it not for this structure. In like manner when the 

 nests are placed in sedges or grasses winds alter the nests to such an extent that 

 the young or eggs would be endangered if no sill were there to prevent tlie 

 catastrophe. 



Several observers have reported mud in the lining of the nests, but 

 Dr. Welter and others have failed to note it ; perhaps some mud may 

 be brought in accidentally with material secured from the muddy 

 floor of the marsh ; it seems doubtful if the wrens every carry in mud 

 intentionally. 



The long-billed marsh wrens are notorious for building extra or 

 dummy nests, which are almost never occupied as brood nests. These 

 are built by the males, mainly during the 10 days or so intervening 

 between the arrival of the males and the coming of the females. 

 Anywhere from 1 to 10, usually not more than half a dozen, are more 

 or less incompletely constructed by a single male within the limits of 

 his territory. We do not fully understand the reason for these extra 

 nests; several theories have been advanced to account for the habit, 

 which is not wholly confined to this species, but none of the theories 

 appears wholly satisfactory. The most plausible theory seems to be 

 that it gives the birds an outlet for surplus energy during the period 

 of sexual activity, for it almost always ends soon after the females 

 arrive and mating takes place. These male nests are never as fully 

 completed as are the brood nests ; they usually do not go beyond the 

 first stage mentioned above, and are often abandoned before they 

 reach even that stage of completion. There is little evidence that they 

 are ever used as brood nests, or as sleeping places for the males, or as 

 territorial land marks. 



A. D. DuBois mentions in his notes a nest that was of the "usual 

 construction except that the top of the nest was covered by green 

 leaves bent over and woven together over the top. All the previous 

 nests observed here, having the green leaves woven over (nearly a 

 dozen so noted) were empty nests." 



Milton B. Trautman (1940) noted that, out of 208 nests, observed 

 at Buckeye Lake, Ohio, 161 had their openings facing toward the 

 south or west. There was one colony, "which was an exception, for 

 11 of 19 nests opened toward the northeast." 



Eggs. — The marsh wren's set may consist of 3 to 10 eggs ; the larger 

 numbers are rare; 5 or 6 seem to be the commonest numbers. They 



