Population Evaluation 



Population Estimates 



Our data (Chapter 2) indicated that reliable estimates of 

 mule deer populations could be made in riverbreaks habitat. 

 Similar findings were reported for other eastern Montana 

 populations (Wood et al . 1989, Watts unpubl . , Knapp unpubl . , 

 Jackson unpubl . ) . Use of complete-coverage aerial surveys and 

 Lincoln Indexes with at least 20-25 well-distributed radio- 

 collared deer was an appropriate method. Observability indexes 

 and other results were generally consistent when the same 

 pilot and observer were used. Once the spectrum of survey 

 conditions had been covered, reasonable estimates of the 

 observability of deer on any particular flight could probably 

 be made by an experienced observer even without marked deer. 

 Surveys with the Bell 47 helicopter were less sensitive to 

 variations in weather conditions and ground cover than those 

 with the Piper SuperCub. 



Helicopter surveys and multiple fixed-wing surveys may 

 often be too expensive and time consuming for widespread use 

 by management personnel. When that is the case, and where an 

 estimate of recruited population size is the most important 

 information desired, we recommend full-coverage, early spring 

 surveys with a Piper SuperCub. Under proper conditions, early 

 spring is the most efficient time for survey, and it also most 

 accurately measures net annual recruitment. We counted 

 similar proportions of the population during early spring 

 surveys with the SuperCub as we did with the helicopter in 

 either early winter or spring. 



For best results, correct timing of these spring surveys 

 is very important. The objective is to time flights such that 

 the majority of deer are feeding on open ridges and south 

 facing slopes where new green growth first appears. We 

 obtained best results in flying when new growth of grasses and 

 spring forbs had only recently started. The highest 

 proportion of the population was observed in the open, and 

 deer spent more time during the day in the open when flights 

 were made before new growth had started under the forest 

 canopy and before large amounts of new growth were available 

 in open areas. Under these conditions, effective surveys can 

 be flown during all hours of daylight except immediate mid- 

 day. 



Our data on deer distribution and dispersal patterns had 

 important implications to the proper establishment of study 

 areas and trend areas for measurement of population trend. 

 When establishing these areas, marginal deer habitat must be 

 included along with core habitat. On our study area, 



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