May, 1921 NESTING OF THE STEPHENS FOX SPARROW 85 
I wish here to thank Mr. K. L. Skinner for his kindness in sending me a 
deseription of the set of eggs in his collection, Mr. R. C. Harlow, who has kindly 
helped me in the same way, and Mr, A. O. Treganza for the loan of specimens. 
Claremont, California, February 7, 1921. 
WEIGHTS AND PLUMAGE OF DUCKS IN THE RIO GRANDE VALLEY 
By ALDO LEOPOLD 
cies killed during the open season in the Rio Grande Valley between Socorro 
and Albuquerque, New Mexico. These weights, all plotted as colored 
points (one color representing each species) on codrdinates of time in weeks and 
weight in pounds, respectively, give an interesting one-page graphic record of 
seasonal weight changes, maximum and minimum weights, comparative weights 
of species, seasonal abundance of species, and comparative abundance of spe- 
cies. It is impracticable to publish the colored graph, but the following data ob- 
tained from the graph, and questions and conclusions suggested by it, may be of 
interest.’ 
S INCE 1917 I have recorded the weights of about 300 ducks of fifteen spe- 
TABLE OF WEIGHTS IN POUNDS 
Maximum Minimum 
Species No. Extreme General Extreme? General 
NUON GG eee 101 Boa) 3.00 Let 2.00 
Black Mallard ............<...... Wy OES gies fer re Rebs Doce | e tMiay cere 
eg WimcHN lem ees es ee aia 2.37 2.10 1.30 1.50 
MCOMW 2... ccsb.etc-ckiecese OO 2.63(?) 105 Veils 1.30 
CP CTE seek ee 9 2.00 1.90 i hea Dg eee 
Green-wing Teal ................ 42 RS eee are ak cs O31) <a De ee 
Blue-wing Teal .................. 13 sO)0) ah as ee ee ees Olnetsen’ ) | geeee 
S15 C1052) 0 0 0 eee nee 37 1.69 1.50 .95 1.00 
WAMVAS-DACK .....2:-22--25.c02.-2-5- iC AG See il oe ae MTs 1.90 os 
CECI A Ws. 5 os es eee 3 NUS a = =e ee a) en a eee 
Bluebill (both sp.)............ 4 ey eed 8) hee oe 1 ie Se eed 
Barmlenead! 2.2.2.2... 2620... 4 Off R pe cee 75 Weta. en 
Peay: DUCK. .....22..2-2-+--c0-<2-- 4 eS Sie! AE ek o0mery chs.’ 
The graph shows that Mallards attain their greatest weight in early Novem- 
ber and decline shghtly but steadily durimg December and January. Pintails 
stay about stationary, while Gadwalls and especially Widgeons inerease steadily 
throughout the season. I know of nothing in their respective food habits to ac- 
count for this. It suggests the possibility that weight may increase with maturity 
of plumage, more or less independently of food supply and food habits, it being 
a manifest fact, known to every hunter, that Mallards in this region attain nearly 
full maturity of plumage in November, while the other three do not show full 
feather until the middle of the winter. Spoonbills and Teals seem to decrease in 
1Some preliminary “Notes on the Weights and Plumage of Ducks in New Mexico” 
were published in the Condor, XXI, May, 1919, pp. 128-129. 
"These extreme minimum weights should be accepted with reservations because of 
the possibility of the figures containing crippled birds. No cripples were knowingly in- 
cluded, but occasionally even an active and apparently healthy bird has sustained wounds 
which may have affected its weight. 
