getting alot of lag/fps spikes usually happens at night with alot of mobs

---- Minecraft Crash Report ----
// Shall we play a game?

Time: 7/2/13 9:28 PM
Description: Manually triggered debug crash

java.lang.Throwable
	at atn.k(SourceFile:1232)
	at atn.S(SourceFile:662)
	at atn.d(SourceFile:618)
	at net.minecraft.client.main.Main.main(SourceFile:101)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Affected level --
Details:
	Level name: MpServer
	All players: 1 total; [bcx['GothicVash'/199, l='MpServer', x=-531.53, y=64.62, z=241.06]]
	Chunk stats: MultiplayerChunkCache: 441
	Level seed: 0
	Level generator: ID 00 - default, ver 1. Features enabled: false
	Level generator options: 
	Level spawn location: World: (217,64,219), Chunk: (at 9,4,11 in 13,13; contains blocks 208,0,208 to 223,255,223), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
	Level time: 1716256 game time, 1868199 day time
	Level dimension: 0
	Level storage version: 0x00000 - Unknown?
	Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
	Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
	Forced entities: 108 total; [tq['Spider'/6569, l='MpServer', x=-587.34, y=24.00, z=298.75], tt['Zombie'/6573, l='MpServer', x=-598.50, y=63.00, z=162.50], tc['Creeper'/6589, l='MpServer', x=-605.50, y=14.00, z=200.50], tc['Creeper'/6588, l='MpServer', x=-607.63, y=14.00, z=203.89], tq['Spider'/6578, l='MpServer', x=-592.50, y=63.00, z=190.50], to['Skeleton'/4095, l='MpServer', x=-573.50, y=47.00, z=287.50], to['Skeleton'/4097, l='MpServer', x=-575.50, y=47.00, z=287.50], rw['Sheep'/305, l='MpServer', x=-607.81, y=68.00, z=167.50], to['Skeleton'/4096, l='MpServer', x=-573.50, y=47.00, z=288.50], rw['Sheep'/304, l='MpServer', x=-603.34, y=63.00, z=168.84], to['Skeleton'/4099, l='MpServer', x=-518.50, y=36.00, z=318.50], tt['Zombie'/307, l='MpServer', x=-603.50, y=35.00, z=206.50], rv['Pig'/306, l='MpServer', x=-605.97, y=63.00, z=191.09], rv['Pig'/309, l='MpServer', x=-595.13, y=64.00, z=202.63], rv['Pig'/308, l='MpServer', x=-599.94, y=64.00, z=202.97], tt['Zombie'/4103, l='MpServer', x=-552.50, y=23.00, z=200.50], rv['Pig'/311, l='MpServer', x=-598.81, y=63.00, z=217.09], rv['Pig'/310, l='MpServer', x=-595.09, y=64.00, z=199.94], tt['Zombie'/4104, l='MpServer', x=-549.50, y=23.00, z=198.50], rv['Pig'/312, l='MpServer', x=-599.91, y=63.00, z=210.03], tc['Creeper'/4107, l='MpServer', x=-550.31, y=23.00, z=201.59], rl['Bat'/315, l='MpServer', x=-601.75, y=14.10, z=268.50], tc['Creeper'/4106, l='MpServer', x=-549.97, y=24.00, z=199.56], tt['Zombie'/4109, l='MpServer', x=-580.50, y=14.00, z=220.50], sr['entity.MinecartChest.name'/317, l='MpServer', x=-601.50, y=25.52, z=300.50], rv['Pig'/319, l='MpServer', x=-603.88, y=63.00, z=314.13], rl['Bat'/2701, l='MpServer', x=-571.25, y=38.10, z=219.47], rl['Bat'/2703, l='MpServer', x=-555.75, y=37.86, z=205.53], tc['Creeper'/290, l='MpServer', x=-609.41, y=14.00, z=198.00], tq['Spider'/4115, l='MpServer', x=-602.63, y=63.00, z=219.50], rl['Bat'/2688, l='MpServer', x=-565.91, y=35.00, z=316.69], tt['Zombie'/342, l='MpServer', x=-588.56, y=20.00, z=207.88], rl['Bat'/341, l='MpServer', x=-569.44, y=25.87, z=191.75], tc['Creeper'/350, l='MpServer', x=-590.50, y=20.00, z=288.50], rl['Bat'/348, l='MpServer', x=-580.06, y=14.10, z=269.16], tc['Creeper'/344, l='MpServer', x=-584.50, y=23.00, z=221.50], rz['Squid'/374, l='MpServer', x=-544.47, y=61.34, z=196.28], to['Skeleton'/6594, l='MpServer', x=-597.50, y=19.00, z=229.50], to['Skeleton'/6595, l='MpServer', x=-596.50, y=19.00, z=228.50], to['Skeleton'/376, l='MpServer', x=-538.56, y=12.24, z=238.70], rv['Pig'/379, l='MpServer', x=-537.03, y=63.00, z=247.03], to['Skeleton'/6593, l='MpServer', x=-596.50, y=19.00, z=231.50], rn['Chicken'/378, l='MpServer', x=-544.44, y=63.02, z=250.34], bcx['GothicVash'/199, l='MpServer', x=-531.53, y=64.62, z=241.06], rv['Pig'/358, l='MpServer', x=-566.97, y=63.00, z=201.47], rl['Bat'/359, l='MpServer', x=-572.53, y=25.10, z=253.00], sr['entity.MinecartChest.name'/352, l='MpServer', x=-587.50, y=33.52, z=303.50], rl['Bat'/354, l='MpServer', x=-570.49, y=15.87, z=292.05], tt['Zombie'/4969, l='MpServer', x=-577.50, y=16.00, z=283.50], tq['Spider'/364, l='MpServer', x=-576.22, y=63.00, z=257.50], tt['Zombie'/4968, l='MpServer', x=-578.50, y=16.00, z=281.50], sr['entity.MinecartChest.name'/366, l='MpServer', x=-574.50, y=24.52, z=309.50], tt['Zombie'/4970, l='MpServer', x=-576.50, y=16.00, z=282.50], tc['Creeper'/4973, l='MpServer', x=-559.50, y=39.00, z=170.50], tc['Creeper'/4972, l='MpServer', x=-558.50, y=39.00, z=169.50], rv['Pig'/361, l='MpServer', x=-566.94, y=63.00, z=255.88], tc['Creeper'/4975, l='MpServer', x=-559.50, y=39.00, z=172.50], rv['Pig'/362, l='MpServer', x=-570.13, y=63.00, z=244.19], tc['Creeper'/4974, l='MpServer', x=-558.50, y=39.00, z=170.50], tq['Spider'/363, l='MpServer', x=-574.50, y=63.00, z=254.47], tt['Zombie'/410, l='MpServer', x=-526.03, y=47.00, z=185.53], rv['Pig'/411, l='MpServer', x=-524.72, y=70.00, z=181.47], rl['Bat'/6102, l='MpServer', x=-497.41, y=15.00, z=263.84], tc['Creeper'/415, l='MpServer', x=-506.41, y=40.00, z=187.97], td['Enderman'/4543, l='MpServer', x=-601.41, y=63.00, z=266.50], tt['Zombie'/412, l='MpServer', x=-519.50, y=41.00, z=202.69], rl['Bat'/403, l='MpServer', x=-544.28, y=39.10, z=307.94], rl['Bat'/400, l='MpServer', x=-542.69, y=15.10, z=235.63], to['Skeleton'/401, l='MpServer', x=-541.50, y=40.00, z=231.91], rv['Pig'/395, l='MpServer', x=-531.13, y=64.00, z=193.13], rz['Squid'/394, l='MpServer', x=-541.69, y=58.34, z=191.50], rv['Pig'/392, l='MpServer', x=-529.09, y=70.00, z=179.94], rz['Squid'/398, l='MpServer', x=-544.84, y=56.38, z=210.22], rz['Squid'/397, l='MpServer', x=-526.62, y=57.34, z=231.66], rz['Squid'/396, l='MpServer', x=-526.76, y=56.00, z=227.47], tt['Zombie'/385, l='MpServer', x=-534.50, y=29.00, z=175.50], rn['Chicken'/390, l='MpServer', x=-535.47, y=66.00, z=178.63], rv['Pig'/446, l='MpServer', x=-473.13, y=64.00, z=164.84], rv['Pig'/447, l='MpServer', x=-479.69, y=64.00, z=167.94], rv['Pig'/432, l='MpServer', x=-477.03, y=64.00, z=192.03], to['Skeleton'/433, l='MpServer', x=-480.44, y=62.17, z=257.50], rl['Bat'/434, l='MpServer', x=-489.49, y=26.00, z=314.63], tc['Creeper'/435, l='MpServer', x=-489.97, y=26.00, z=313.44], tc['Creeper'/436, l='MpServer', x=-494.50, y=27.00, z=312.50], rv['Pig'/429, l='MpServer', x=-483.31, y=63.00, z=174.16], rv['Pig'/430, l='MpServer', x=-482.66, y=63.00, z=180.13], rv['Pig'/417, l='MpServer', x=-503.03, y=71.00, z=184.66], rn['Chicken'/421, l='MpServer', x=-507.63, y=68.00, z=196.53], tt['Zombie'/422, l='MpServer', x=-506.59, y=63.00, z=212.41], rl['Bat'/2686, l='MpServer', x=-586.75, y=48.10, z=291.50], rl['Bat'/2685, l='MpServer', x=-586.75, y=47.00, z=292.75], tc['Creeper'/455, l='MpServer', x=-457.50, y=36.00, z=237.50], rv['Pig'/454, l='MpServer', x=-460.25, y=63.00, z=207.78], rv['Pig'/453, l='MpServer', x=-457.06, y=63.00, z=183.94], rv['Pig'/452, l='MpServer', x=-452.84, y=64.00, z=172.03], tc['Creeper'/450, l='MpServer', x=-469.50, y=14.00, z=297.50], to['Skeleton'/6068, l='MpServer', x=-521.82, y=33.00, z=244.26], rl['Bat'/5252, l='MpServer', x=-460.22, y=43.67, z=323.50], tt['Zombie'/3851, l='MpServer', x=-519.34, y=63.00, z=209.78], to['Skeleton'/6077, l='MpServer', x=-527.50, y=33.00, z=237.50], to['Skeleton'/6076, l='MpServer', x=-526.50, y=33.00, z=239.50], to['Skeleton'/4560, l='MpServer', x=-611.50, y=20.00, z=242.50], tc['Creeper'/3841, l='MpServer', x=-593.50, y=21.00, z=285.50], tc['Creeper'/4559, l='MpServer', x=-601.50, y=43.00, z=205.50], tt['Zombie'/4556, l='MpServer', x=-573.50, y=17.00, z=220.50], tc['Creeper'/4554, l='MpServer', x=-546.94, y=28.00, z=199.47], tc['Creeper'/4553, l='MpServer', x=-561.50, y=40.00, z=197.50], tc['Creeper'/4550, l='MpServer', x=-590.50, y=63.00, z=270.50]]
	Retry entities: 0 total; []
Stacktrace:
	at bcu.a(SourceFile:284)
	at atn.b(SourceFile:1743)
	at atn.d(SourceFile:627)
	at net.minecraft.client.main.Main.main(SourceFile:101)

-- System Details --
Details:
	Minecraft Version: 1.6.1
	Operating System: Windows 8 (amd64) version 6.2
	Java Version: 1.7.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 161641536 bytes (154 MB) / 467402752 bytes (445 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 16931 (948136 bytes; 0 MB) allocated, 2 (112 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
	Launched Version: 1.6.1
	LWJGL: 2.9.0
	OpenGL: Intel(R) HD Graphics GL version 4.0.0 - Build 9.17.10.2932, Intel
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Pack: Default
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 7120 (398720 bytes; 0 MB) allocated, 12 (672 bytes; 0 MB) used