12-13 



day; highest concentrations of birds occurred shortly after low tide on 

 mudflats and outer beach habitats and after high tide on inner beach 

 habitats. Thus, the disj^roportionate amount of June censusing at high 

 tide in New Haven probably cxxolains the low recordings of shorebird 

 number and species during this month. 



Gull species diversity remained constant throughout the year 

 (Figure 12-5) . Although gulls are considered migratory species, there 

 is considerable overlap in ranges of different populations. In addition, 

 some migrations may be very short, resulting in no noticeable influx or 

 outflow from an area in either species diversity or numerical abundance. 



Abundance 



The total number of birds observed ranged from just under 

 27,000 in 1974 to over 40,000 in 1975 (Appendix Table 12-2). Such year- 

 to-year fluctuation in numbers is expected due to factors related to 

 sampling, such as weather, tide level at time of sampling, coincidence 

 of observations with timing of population movements, and variations inherent 

 in visual population estimation, as well as short- and long-term fluctuations 

 in abundances of individual species populations. 



In each study year, bird counts began increasing in November, 

 and remained at high levels, peaking in February (Figure 12-6) . Numbers 

 then dropped off with lowest numbers of birds observed in the period of 

 May through July. Waterfowl numbers were highest in the winter months 

 while shorebird numbers peaked in the summer. Gulls were present in 

 large numbers all year and showed no pattern of fluctuation (Figure 12- 

 3, 12-4 and 12-5) . 



The overall seasonal abundance of birds is due to the same 

 factors that explain seasonal differences in species diversity, i.e. 

 timing of migrations by the various groups. This trend in both seasonal 

 species diversity and seasonal fluctuations in overall numbers was 

 present in all five years of study. 



