UNIVERSITY of PENNSYLVANIA 
PHILADELPHIA 19104 
The College 
Department of Biology 
Joseph Leidy Laboratory 
of Biology 
7 Sept. , 1964 
Dear Martin: 
Glad to get your recent letter, although sc.Jewhat dis- 
turbed that you mentioned, but did net catalogue, some recent un- 
pleasantness. Sometimes I wish you weren’t such a genius at saying 
nothing personal in a litter - 1 do hope that whatever this was has 
meant no personal hardship for you or for the Rubinof f s . How are they 
making out , incidentally? Glad to hear you’ve got Stan Rand, 1 know 
you will be extremely pleased with him. When does he arrive? 
Sue and I had a delightful Mexican holiday, blessed by the 
most incredibly perfect weather I’ve ever had on a trip. We took 
3 days from the border to wander slowly down the eastern side to 
Mexico City through the spectacular eastern slopes of the Sierra, 
ent only 3 days in the City then went up and camped on i*it. Popo- 
catapetl; climbed up to about the lower limit of snow (somewhat over 
14,000’ at that time, I think). Went on down to the east coast again 
at Veracruz, then made a long loop up past M.City to the Central 
Plateau and came north through the deserts, collecting cacti to 
breed bac?< here, Finally came out at Laredo and dropped down to McAllen 
Texas to finish some observations on Tyrannus couchii , cur new king- 
bird. (We’d designed parts kef the trip to look at its habitats in 
Mexico and had found it still somewhat vocil even tho* in the post- 
breeding season. Surprisingly , or perhaps not so, vie got what may 
be evidence of introgressive hybridization with T. n elancholicus . al- 
though our data are too scanty to prove this. We got good T. couchii 
vocalizations as far south as we got- near the end of its range - 
and these are very different in form from T. mel, as well as being 
slower and at about \ the pitch of the latter, tie also got, although 
not certainly from the same individuals, use of the simplified T. 
mel patterns, but at the pitch of T. couchii, and slowdd to its 
speed (ie. they sounded like T. mel tapes played at f speed). These 
vocalizations would be redundant in that population as we heard the 
T. couchii equivalents. Must someday return in breeding season.) 
In Texas, however, we both came down with dysentery, Sue quite severely 
She is still net fully recovered after about 15 days, but is very 
greatly improved. I'm at present sweating out the preparaticn of some 
lectures. AA ave been talking with Martin Cody and shall confer with 
MacArthur when he returns (in a week or so) about the towers they 
want - shall se^-if we can straighten out the issue; Cody at least 
knows exactly where he wants a tower. He’ll be down after Christmas. 
Before I continue, here are some notes I made for you in a 
mixed flock on Mt. Pcpo in the pines around our campsite (about 13,000’) 
Forest mature, probably Pinus hartwegi , rich bunch grass understory, 
grazed by cattle (net severelyX Floe ’ ; in both pines (of which thhre 
were rather few young ones) and grass (ie., on ground). The most 
