LINCOLN'S SPARROW 1445 



the fourth egg as between 13 days, 1 hour, 3 minutes and 13 days, 16 

 hours, 20 minutes, and most probably about 13 days and 6 hours, 

 from about 5 a.m. June 4 to about 11 a.m. June 17. 



The attentivity rhythm at this nest was determined with a therm- 

 istor bridge recorder (Speirs and Andoff, 1958) which showed that 

 on June 5 the female spent more time off than on the nest. Four 

 attentive periods averaged 34 minutes in length (13, 45, 46, and 33 

 minutes) while four inattentive periods averaged 62 minutes (83, 

 28, 12, and 127 minutes), this in spite of the fact that it was a cool 

 day with some light rain. This was the second day of incubation and 

 the attentivity rhythm apparently was not yet fully established. 

 On June 8, the fifth day of incubation, and a clear, mild day, the 10 

 attentive periods averaged 20.4 minutes ranging from 17 to 40 minutes, 

 while 11 inattentive periods averaged 6.9 minutes ranging from 2 to 15 

 minutes; from 9:32 a.m. to 2:12 p.m. the incubating bird spent 75 

 percent of its time on the nest and 25 percent off. On the morning of 

 June 11, the eighth day of incubation, attentive periods of 25, 54, and 

 19 minutes were broken by inattentive periods of 3 minutes and 1 

 minute. The increased attentivity on this day may have been in- 

 fluenced by the overcast weather though temperatures remained about 

 the same, or may have been an expression of the intensification of the 

 incubation habit. Nice (1937) found a similar shortening of the 

 inattentive periods in the song sparrow as incubation progressed. 



We have no evidence of the male Lincoln's sparrow calling its mate 

 off the nest at intervals during incubation as M. M. Nice (1943) writes 

 that song sparrow males do. The Lincoln's sparrow males apparently 

 sing very little during the incubation period; in this also they differ 

 from the song sparrow. In fact, we did not see nor hear our particular 

 Lincoln's sparrow male after the day the fourth egg was laid until the 

 young hatched. The male bird at our 1956 nest did some singing 

 during the incubation period, chiefly in the very early morning. 



When the female was flushed from the nest on June 7, 1957, instead 

 of flying, she ran out along the ditch. Again on June 9 she did not 

 flush until the last minute and then ran along the ditch "like a little 

 mouse" for a yard or two, then flew very low, just clearing the ground 

 cover, to the forest edge north of the nest. She did not scold or utter 

 any sound when flushed, and she did not leave the nest until the grass 

 over it was parted to show it to a visiting naturalist. On June 12 

 while changing the chart on the nest recorder the observer twice 

 jumped the ditch within a few feet of the nest, and the bird did not 

 leave the nest. 



Young. — Notes were made on the development of the 1956 Dorion 

 young five times during their nest life. On June 24, when, pre- 

 sumably, the nestlings were a day old, they had an egg tooth on the 



