Food and feeding of Little Tern on the Hooge Platen

Food and feeding of Little Tern on the Hooge Platen

November 16th 2012, Minsmere, SuffolkRene Beijersbergen

Distribution and population

Coastal breeders: Common tern, Little tern and Kentish plover

In this contribution on Little Tern little attention for….

FloodingsHabitatselectionDevelopment of vegetationCompetitionPredation

But I like to focus on food and feeding.

Breeding and feeding within short range

april (n=6) may (n=363)

june (n=167)

juli (n=139)0

50

100

sand eel herring

Little tern’s prey

Distribution of clutchsize of Little tern

0

25

50

n=138

n cl

utch

es (%

)

clutch of 3 2 1

Start of laying, clutchsize and weight in Little tern

0

14

28

150 170day (may 31st = day 151)

weig

ht o

f clu

tch

(g)

clutch 3 2 1

1993 20060

40

80

120

160

Change in search time, diving success and clutch weight

searchtime (s) divingsuccess (%)clutchweight (g)

inde

x (1

993

= (1

00)

Fish intake and clutch weight

Clutch size in the period 1990 – 2010 was between 1.78 and 2.82

4 6 11 13 15 18 21 23 260

25

50

75

100

Arrival, food and settlement of Little Tern

resting (n) pairs courtshippingpairs breeding n dives x10 (100 s searchtime)

may

2 3 5 5.80

25

50

75

100

Succesfull dives (%) in relation to number of dives (n/100 s search time) for Sandeel

Breeding between 2002 and 2010

Hooge Platen• Start egg laying between

May 3rd and June 4th• Average date May 19th

• Number of breeding pairs between 0 – 250

• Average 112 pairs

Foreshore• Start egg laying between

May 4th and May 25th• Average date May 14th

• Number of breeding pairs between 0 – 120

• Average 36 pairs

0

2

4

6

8

Weight of fish (sandeel or herring) caught in the striped zone

Foreshore Bol

wei

ght (

g/10

0 s

sear

ch ti

me

Litle terns have no choice but to breed close to the feeding site

Are (Little) terns flexible when food is scarce……?

• They are flexible in the clutchsize

• They are flexible in the start of egg laying

• They are flexible in choosing a breedingsite

Number of breeding pairs of Little tern on the Hoge Platen Nature Reserve

0

50

100

150

200

250

1978 1984 1990 1996 2002 2008 2012

Little Tern Lineair (Little Tern)

Sandeel becomes less abundant…

1985-1991 (n=1286)

1992-1998 (n=507)

1999-2005 (n=614)

20006-2012 (n=2088)

0

20

40

60

80

Preyspecies of Little Tern in four 7-years periods between 1985 - 2012

Sandeel Herring

(%)

Around the North Sea Sandeel becomes less abundant….

• Global warming and climate change

• Industrial fisheries

• Local dredging of harbours and shipping channels

So what can we conclude…..• For succesfull breeding Little Tern seems to be dependant on

both 0-year Sandeel and Herring

• During pre-breeding, egg laying and breeding they depend mainly on Sandeel

• Number of breeding pairs, clutchsize and site depend on the availability of Sandeel

• Terns are dependant on small fish for the young chicks and bigger fish for themselves

• On the continent the largest colonies we find close to the seashore