710 METHODS A^D TECHNIQUES 



preliminary experiments were run at the Research Center to find a method hy which the signs 

 left where birds were killed or nests broken up rould furnish a I)asis for recognizing the 

 predator responsible. 



Observations of penned wild animals checked by an occasional experience in the field when 

 predators were surprised in the act of breaking up a nest, formed the basis for the following 

 key. One must remember, however, a key of this kind must be confined largely to typical 

 examples while in prartire one frequently enrounters situations where the evidence is conflict- 

 ing. This is particularly true with respect to eggs destroyed toward the end of the incubation 

 period. In such cases, the different indications must be weighed against each other as well 

 as against circumstantial information such as the presence of tracks or hair. Also, the relative 

 probability of the various suspected species finding the nest location must be considered. 

 Beyond this, one may record the quality of the evidence by rating the diagnosis as excellent, 

 good or fair. 



Furthermore, the key deals only with the characteristics of wild predators, except that the 

 dog and house cat are included, and also applies only to species found in New York. It 

 assumes that nests destroyed as a result of such causes as fire, flood or the activities of man 

 will be recognized by the investigator from other sources. 



Key for Diagnosing Predators Responsible for Breaking up Grouse Nests 



A. All or most of clutch intact in nest 



1. All eggs in nest, cold Female probably killed* 



2. Three or four eggs missing; remainder 



usually still being incubated Foxes frequently filch a few eggs at a 



time from a nest. Crows and red squir- 

 rels may do the same thing. Further- 

 more, any species which carries the eggs 

 away from the nest may be interrupted 

 and thus leave this result^ 



B. Nest empty of eggs or shell remains but structure not disturbed^ 



1. Remains of individual eggs left at points from 1 to 1?> feet from nest in different 

 directions 



a. Shell usually retaining its general spherical form 



n) Shell irregularly opened at one side: frequently 

 found on stumps 



(a) Punctures usually conforming to shape of 

 crow's bill, frequently with smaller out- 

 ward punctures opposite Crow 



(b) Opening not having punctured ajipear- 

 ance; two portions of shell sometimes 

 separated : yolk or other egg contents 

 occasionally found smeared or tree trunk: 



all eggs seldom taken Red Squirrel 



* If the rrnminii ran lir (oiiikI iIii'v may give Boine indication of thr |>rr<]alnr respnnftiblc. 



A Soc B for rharnrlrriKtir melltndii of tlip«c ipteivf. 



t In flfldition to Ihr Rprrieii limn! nndrr llti* rstrsory the blnrk snnkr, wliirli occniiionally Iihb lircn fount! guilty. vrouM Iravi, the 



nml In Ihia condition, Hrrauiir it awallowa the CRpt whotr. ratrliinp tllP individual Willi ila loot it the only way of apprrlipnd- 



in|[ it. 



