Recording long-term field observations of organisms can be helpful in determining the abundance and diversity

Kirsten Wasson

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• Publié par: Nisig
• Nombre de lectures: 77
• Langue: English

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BIRD MONITORING TRENDS FROM DATA COLLECTED BY SUE SHAW

Analysis and Report by Susie Fork, January 2002

The information gathered by counting the numbers and kinds of animals found in a particular

ecosystem can tell us much about the value of these areas to animals, and changes in abundance and

diversity of particular groups of animals may also reflect underlying changes in the habitat. Birds

are ideal for studies of wetlands, because they are often present in great numbers here, and many are

easily identified from a distance. Important measures include overall bird diversity and abundance

of the entire study area, as well as comparisons of different sites within the area.

While faithfully carrying out water monitoring, volunteer Sue Shaw decided also to take on the

challenge of keeping detailed notes of the abundance and diversity of birds she saw at each of the of

26 sites during 1989-2000. Stations were located the along entire length of the slough from the

mouth at Moss Landing and adjacent areas all way up to the head of the slough. Additionally, Sue

also monitored stations further south at Salinas River, Moro Cojo, and nearby locations. In all, 29

different types of birds were recorded at Elkhorn Slough and environs. More commonly seen birds

included loons, cormorants, pelicans, gulls, terns, shorebirds, herons, egrets, ducks, geese, coots,

grebes, and kingfishers.

The total abundance of birds counted at Elkhorn Slough and adjacent areas did not change over

the 8-year period (for statistical reasons, only data from 1992-1999 were analyzed), which is good

news. Abundance of individual bird groups (e.g. gulls, terns, cormorants, Great Blue Herons,

egrets, and geese) also remained unchanged. Two exceptions were coot and loon numbers, which

increased significantly over the 1990s. Others whose abundance increased slightly included

American Avocets, Black-necked Stilts, ducks, geese, and pelicans.

Annual totals of overall bird abundances varied between sites. Salinas River Lagoon took top

honors with a total of nearly 9000 birds, most of which were gulls (7000) and pelicans (800)! The

remaining included terns and cormorants, and lesser numbers of shorebirds, grebes and coots. Sites

with the lowest abundances were the Porter marsh side of Hudson Landing, Upper and Lower Pond

at Azevedo Ranch, and Moss Landing Rd. (less than 50 birds each). Abundance of specific bird

groups also varied significantly between sites for pelicans, loons, ducks, coots, gulls, terns, egrets,

American Avocets, Black-necked Stilts, shorebirds, and Belted Kingfishers. For example, the

highest numbers of ducks (> 200 birds) were observed at Skippers, while coots were most abundant

at North Marsh at Strawberry Rd. and Moro Cojo (> 100 at each site). Shorebirds numbers were

highest at Strawberry (>400), Jetty Rd. (200), Kirby Park and the railroad side of Hudson’s Landing

(>100 at each site). Waders (herons, egrets, avocets and stilts) were most abundant at Strawberry

(North Marsh) and North Potrero (>50 birds at each site). Of the waders, the egrets were found

mostly at Jetty Rd. and Reserve Bridge (15-20 birds at each site). Over the years several Belted

Kingfishers were consistently observed at South Marsh and East Bennett Slough.

Bird diversity, like bird abundance, also varied significantly between the sites. The sites with the

highest diversity were Jetty Rd. and North Potrero, each supporting more than 12 types of birds

(including loons, cormorants, pelicans, gulls, terns, shorebirds, herons, egrets, ducks, geese, coots,

grebes, and kingfishers). At the other extreme, Carneros Creek Rd. and Monterey Dunes Way each

had fewer than four bird types. Total bird diversity also varied significantly over the years. The

highest diversity of birds was counted from 1996 to 1998, while the lowest diversity was observed

in 1992.

So the good news is that it appears that bird numbers have been stable over the last decade and

diversity may even be increasing. The time and dedication of the volunteers at Elkhorn Slough

towards monitoring projects such as bird censusing are a valuable contribution to our understanding

of this rich and diverse habitat.

FIGURE 1. SAMPLING STATIONS FOR VOLUNTEER WATER QUALITY MONITORING.

0

200

400

600

800

1000

1992

1993

1994

1995

1996

1997

1998

1999

Fig. 2. Total Abundance of Birds vs. Year.

Abundance was steady over time (ANOVA, P=0.93).

0

10

20

30

40

50

60

1992

1993

1994

1995

1996

1997

1998

1999

Fig. 3. Coot Abundance vs Year.

Abundance increased from 1992 – 1999 (ANOVA P=0.03).

0

200

400

600

800

1000

1200

1400

1600

1800

BackBennett

Cameros

EastBennett

HudLdgLP

HudLdgRC

Jetty

Kirby

LowerPond

MidPond

MLRdS

MLRdN

MontDuneWy

MoroCojo

NPotrero

NMarsh

NPotrero

ResBr

SPotrero

SMarsh

SalRvrBr

SalRvrLgn

Skippers

Strawberry

StruvePond

Tembladero

UpperPond

Fig. 4. Total Annual (Mean) Bird Abundance vs. Site.

Mean abundance differed by site (ANOVA P<0.0001) with the highest numbers at Salinas River

Lagoon (nearly 9000 birds).

0

50

100

150

200

250

BackBennett

Cameros

EastBennett

HudLdgLP

HudLdgRC

Jetty

Kirby

LowerPond

MidPond

MLRdS

MLRdN

MontDuneWy

MoroCojo

NPotrero

NMarsh

NPotrero

ResBr

SPotrero

SMarsh

SalRvrBr

SalRvrLgn

Skippers

Strawberry

StruvePond

Tembladero

UpperPond

Fig. 5. Total Annual (Mean) Scolopacidae (willets, godwits, Sanderlings, sandpipers) Abundance

vs. Site.

Number of shorebirds varied between sites (ANOVA P=.04). Strawberry had the highest count with

over 400 birds.

0

50

100

150

200

250

300

BackBennett

Cameros

EastBennett

HudLdgLP

HudLdgRC

Jetty

Kirby

LowerPond

MidPond

MLRdS

MLRdN

MontDuneWy

MoroCojo

NPotrero

NMarsh

NPotrero

ResBr

SPotrero

SMarsh

SalRvrBr

SalRvrLgn

Skippers

Strawberry

StruvePond

Tembladero

UpperPond

Fig. 6. Total Annual (Mean) Waterfowl (Ducks and Geese) Abundance vs. Site.

Number of birds varied between sites (ANOVA P=.04) with the highest numbers at Skippers

(nearly 250 birds).

0

2

4

6

8

10

12

14

16

BackBennett

Cameros

EastBennett

HudLdgLP

HudLdgRC

Jetty

Kirby

LowerPond

MidPond M

LRdS

MLRdN

MontDuneWy

MoroCojo N

Potrero

NMarsh

NPotrero

ResBr

SPotrero

SMarsh

SalRvrBr

SalRvrLgn

Skippers

Strawberry

StruvePond

Tembladero

UpperPond

Fig. 7. Total Annual (Mean) Diversity vs. Site.

Number of birds varied between sites (ANOVA P<.0001) with the highest numbers at Strawberry,

North Potrero, and Jetty

(12 types of birds at each site).

0

1

2

3

4

5

6

7

8

9

10

1992

1993

1994

1995

1996

1997

1998

1999

Fig. 8. Total Annual (Mean) Diversity Over Time.

The diversity of birds was higher in the late vs the early 1990s (ANOVA P<.02).